By Bjorn Fehrm

Note: The article offered a Video as an example of the effects of not trimming to neutral before hitting Cut-Off. After reviewing the effects of the video in the context of the article, MentourPilot decided we should leave the text but not include the video any longer. MentourPilot’s YouTube channel is an independent initiative to offer the public correct and positive information of all the work which is behind their safe travel in the skies. In the sensitive situation of an ongoing investigation of the crash of ET302, where not all facts are on the table, he concluded after discussing the impression the video left with a colleague, it was not in line with his intent of setting up the channel. In the haste of the change we took this as his company not wanting the video aired, it was not.  As facts in the ET302 case comes forward we will discuss with MentourPilot if this situation changes. 

April 03, 2019, © Leeham News: The crew of Ethiopian Airlines ET302, which crashed with 157 people on board, used the prescribed Stabilator Trim Cut-Out switches to stop MCAS, according to an article by Wall Street Journal today. Yet still, they crashed. We’ve had the information this could indeed be the case for several days, but we didn’t want to speculate in such a sensitive matter.

The Wall Street article cites information coming from the investigation. By it, we can now reveal how it’s possible the aircraft can crash despite using the Cut-Out switches. To verify, we ran it all in a simulator together with MentourPilot Youtube channel over the last days.

Figure 1. ET302 ground speed as long as FlightRadar24 could follow the flight. Source: FR24.

Following procedures can create dangerous situations with original MCAS

The aeronautical world was stunned when ET302 went down in what seemed a case similar to Lion Air JT610. “Why didn’t they use the trim Cut-Out switches?” was the reaction from longtime pilots. “Every pilot in the world knew what to do, weren’t they briefed?”

The information around the ET302 crash, which comes forward piece by piece, points to an almost identical chain of events to JT610. It also points to the pilots being briefed and, to the knowledge we have available, following procedures including the procedures for a wild running MCAS.

How could ET302 then crash? The FAA and Boeing issued an Airworthiness Directive 2018-23-51 on 8th of November 2018 on what Emergency checklist to use to avoid another MCAS caused crash? The crew should execute the “Trim runaway” emergency checklist.

So why didn’t it work, if the crew indeed followed this AD? Here’s why:

Two weeks ago I wrote: the flying with a full nose down Horizontal Stabilator trim was possible on a 737. The pilot could control the aircraft with his elevator control via the Yoke, even against a full nose down MCAS trim. This was verified in a 737 simulator by a US airline. At the time, I asked what the flown speed was? The answer I got was; the typical speeds after Taking Off.

In subsequent discussions with MentourPilot, a YouTube channel with millions of viewers, I was informed this would probably not be true for higher speeds. MentourPilot’s experience when examining hundreds of pilots as Type Rating Examiner for the 737 was the elevator got exceedingly heavy at higher speeds and manual trimming at the slightest miss-trim of the Stabilator from neutral Yoke forces was very difficult.

He also pointed out the high speeds observed in ET302’s FlightRadar24 trace (Figure 1) were logical. It’s a consequence of following the Emergency checklist for “IAS disagree” (IAS is Indicated Airspeed, i.e. the dynamic air pressure experienced by the aircraft) after takeoff.

The combination of the preceding checklist followed by an MCAS Trim Runaway checklist could create a situation where manual trimming after a Trim Cut-Out would be difficult to impossible and would require non-checklist actions.

Combined with the speed which follows from an “IAS disagree” Emergency checklist procedure the Pilot Monitoring (PM) could have problems to move the trim while Pilot Flying (PF) would fight to hold the Yoke against the elevator forces. At a larger miss-trim, the situation is unattainable.

The excessive manual trim forces have been confirmed by an airline pilot which has done 737 test flights after elevator maintenance, where manual trimming needs to be checked. At a miss-trimmed Stabilator, you either have to re-engage Electric trim or off-load the Stabilator jackscrew by stick forward, creating a nose-down bunt maneuver, followed by trim.

Stick forward to trim was not an option for ET302, they were at 1,000ft above ground. According to The Wall Street Journal, the ET302 crew re-engaged electrical trim to save the situation, to get the nose up. It was their only chance. But too late. The aggressive MCAS kicked in and worsened the situation before they could counter it.

Conclusions

We refrain from speculating more on the limited information we have available. What exactly happened in ET302 will be revealed by the preliminary report, which should be issued within days.

We now know that if the Wall Street article and the rumors are correct, the Trim Cut-Out switches were used by the ET302 crew.

We also know the execution of the Trim Runaway checklist as described in the Emergency Airworthiness Directive (AD) did not describe all the consequences of a trim Cut-Out after an MCAS cycle. Here the text from the AD:

In the event an uncommanded nose down stabilizer trim is experienced on the 737-8/-9, in conjunction with one or more of the indications or effects listed below, do the existing AFM Runaway Stabilizer procedure above ensure that the STAB TRIM CUTOUT switches are set to CUTOUT and stay in the CUTOUT position for the remainder of the flight?

An erroneous AOA input can cause some or all of the following indications and effects:

• Continuous or intermittent stick shaker on the affected side only.
• Minimum speed bar (red and black) on the affected side only.
• Increasing nose down control forces.
• IAS DISAGREE alert.
• ALT DISAGREE alert.
• AOA DISAGREE alert (if the option is installed).
• FEEL DIFF PRESS light.
• Autopilot may disengage.
• Inability to engage autopilot.

 Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT.

Nowhere is it described the trim could be impossible to move if the Cut-Out switches were cut at the slightest miss-trim at the speeds flown. And there is no warning on when to move the Cut-Out switches, the checklist says “Cut, then trim manually.” This is not the whole truth.

What exactly happened will be known once the preliminary report is there. Today we know the crowing from Western pilots, “Typical third world crews,” was not called for. Anyone who has tried a correctly set up MCAS situation in a simulator is more muted.

PS. Regarding blowback of the Elevator, can this come into play as I wrote about here? With the information added by MentourPilot the situation seems to get unattainable before a blowback comes into play. We will know more once the ET302 preliminary report is here. DS

Bjorn’s Corner

April 05, 2019, ©. Leeham News: The preliminary accident report of the ET302 crash was released yesterday. It confirmed what we wrote about earlier in the week, the pilots followed the prescribed procedure to stop MCAS. Yet they didn’t make it.

Part of why we presented Wednesday. Here follows additional analysis after studying the information in the Preliminary Crash Report.

Figure 1. The general Flight Data Recorder trace from ET302. Source: ET302 preliminary report.

The report confirmed our assumptions

The report released by the Ethiopian Ministry of Transport is a preliminary report. It follows the structure of the Lion Air JT610 preliminary report.

It confirms what we wrote about earlier in the week, the Flight Crew followed the procedures prescribed by FAA and Boeing in AD 2018-23-51. And as predicted the Flight Crew could not trim manually, the trim wheel can’t be moved at the speeds ET302 flew.

The traces from the report is Shown in Figure 1 and 2 (click on them to make them larger).

Figure 1 shows the general Flight Information traces whereas Figure 2 shows the specific information around MCAS and the signals which affect MCAS.

Figure 2. The Flight Data Recorder trace from ET302 which deals with MCAS related data. Source: ET302 preliminary report.

I have decided to spend a minimum of time on basics, which we’ve gone through several times, and focus on what everyone is now asking themselves: Why did the Crew re-engage the trim and why didn’t they then trim more themselves to combat any MCAS trim?

First the basics.

The activation of MCAS and how it was stopped

The events are very similar to Lion Air JT610 but not identical. At rotation, everything is normal this time (the high AoA was present at rotation for JT610) but 10 seconds after rotation, at 05.38.45 in the traces, the left Angle of Attack (AoA) went high, Figure 2, 10 seconds after line A.

Observe the values are different from JT610. I assume we have the un-corrected AoA values (the Vane values) in this FDR (Flight Data Recorder) trace whereas we had the recalculated Wing AoA values presented in the JT610 FDR traces (raw angle values are higher for the Vanes as explained in previous articles. The airflow along a fuselage nose is curving upward at positive angle against the wind, more so than for the wing).

Stick shaker activates at A but the flight continues pretty normally until the Flaps are raised at B, Figure 2. The trim commands before Flaps up are normal trims from the Pilot Flying (PF, the Captain, Trim Man trace). Autopilot and finally Speed Trim System trims on the Automatic trim trace (to understand Speed Trim and the reason for MCAS, read here and select among the list of articles at the end of the text to learn more).

After Flaps up at B, you have the first MCAS nose down at 1 which stops at 2 (the FFC, Flight Control Computer, trim trace). Between 2 and 3, PF trims against. This causes MCAS to reset and trim again at 3 and it gets interrupted by PF trim at 4. Now MACS is identified and the Pilot Monitoring (PM, the First Officer) cuts trim with Cut Off switches after 5. We know this as the next attack from MCAS at 6 has no effect on Pitch trim units (the trace below FCC trim). Now the fight with MCAS is over and the crew starts turning back to the airfield after 05.40.45, Figure 1 Heading Disp (Displayed) trace.

The Crew finds however they can’t correct the nose heavy trim with the manual wheels, contrary to what is stated in the AD and in their Checklists. Speed is now at Vmo, the maximum design Indicated Air Speed (IAS) for the aircraft, 340kts.

The throttles are left at 94% thrust for the whole flight. This is higher than normal but this is a high takeoff. At 7,600ft it is a full 2,200ft higher than Denver, which is the US Benchmark for high takeoffs. And with Stick Shaker and IAS disagree you keep high thrust and fly a slow climb (the IAS disagree is present in the traces but not mentioned in the report specifically. We don’t have all the Crew callouts and discussions present in the report is my conclusion).

The high speed of 340kts indicated airspeed and the trim at 2.3 units causes the Stabilator manual trim to jam, one can’t move it by hand. The crew is busy trying to hand trim the next two minutes but no trim change is achieved.

At 7 the aircraft nose is dipping (see Pitch Attitude Disp trace) because PF can no longer hold against the Yoke forces we discussed Wednesday (Ctrl Column Pos L/R). PF decides he needs Electric Trim to stop the aircraft from diving. Cut Off switches are put to Electric Trim active. PF successfully trimmed against the last MCAS attack, he can do it again.

The insufficient trim mystery after re-activation of Electric Trim

After 7 PF commands Electric Trim Nose Up in two short cycles. I asked my selves (as did others) why these short trims? They are fighting to get the nose up to the extent they risk switching in the Electric Trim again. Then why not trim nose up continuously or for at least long cycles once Electric Trim is there? It took me several hours to find an explanation. Here my take:

To understand the blip trims one must have flown fast jets at low altitude. At the speed ET302 is flying, 360kts, it’s hypersensitive to trim. The least trim action and the aircraft reacts violently. Any trimming is in short blips.

As PF holds the nose up with a very high stick force, now for a long time, he’s sensitivity to release stick with trim is not there (this is what Pilots do when they trim nose up, otherwise the aircraft pitches up fast). He trims therefore in short blips and has difficulty to judge the trim effect he has achieved. His is not flying on feel. He can’t, he is severely out of trim, holding on to the Yoke with a strong pull force.

Anyone who has flown a grossly out of trim aircraft at high speeds knows your feel is compromised. The sensors you have to rely on are your eyes, not your hands.

PF has the horizon glued to read the aircraft. The result is the short nose-up trims we see. The nose goes up and the stick force needed is reduced. His judgment is; this is enough for now, it was a powerful response. Any MCAS attack I now trim against, then I correct my trim if I need to.

But the aggressive MCAS, trimming with a speed 50% higher than the pilot and for a full nine seconds, kicks in at 8 with a force they didn’t expect. Speed is now at 375kts and MCAS was never designed to trim at these Speed/Altitude combinations. Dynamic pressures, which governs how the aircraft reacts to control surface movements, is now almost double it was when last MCAS trimmed (Dynamic pressure increases with Speed squared).

The Pilots are thrown off their seats, hitting the cockpit roof. Look at the Pitch Attitude Disp trace and the Accel Vert trace. These are on the way to Zero G and we can see how PF loses stick pull in the process (Ctrl Column Pos L). He can barely hold on to the Yoke, let alone pull or trim against.

His reduced pull increases the pitch down further, which increases the speed even more. At 05.45.30 the Pilots have hit the seats again (Accel Vert trace and Ctrl Columns force trace) and can start pulling in a desperate last move. But it’s too late. Despite them creating the largest Control Column movement ever, pitch down attitude is only marginally affected.

We have Control Column displacement this time, JT610 was Force. If the elevator reacts to these displacements, at the Dynamic Pressure we have, we should have seen the diving stop. The lack of reaction to the large Control Column displacement of two Pilots pulling makes me think we now have blowback. This is not a design fault, we are well beyond Vmo. But it explains the rapid dive, unhindered by the Pilots’ actions.

It’s easy to say “Why didn’t they trim then?”. Because they are going down at 20 degrees nose down (which is a lot, a normal landing approach is 3°) and at 400kts. Then you just pull for all you have. And the aircraft is not reacting to the largest Control Column displacement since takeoff. This makes them pull even harder, the aircraft is unresponsive and they are fighting for theirs and all the passenger lives.

A final reflection: Once again we have been given no elevator trace. Why? It’s there, why can’t we see it. It would have given us a better understanding of what’s happening in the last part of the flight.

Bjorn’s Corner

April 12, 2019, ©. Leeham News: In the wake of the 737 MAX accidents an important news event last week went almost unnoticed. After years of preparation, the worldwide coverage of ADS-B via Satellite receivers started with a trial service over the Atlantic.

It’s the Aireon Company which started the trial on April 2^nd together with Nav Canada and UK’s NATS (National Air Traffic Control Services).

Figure 1. The Aireon worldwide Sattelite ADS-B receiver system. Source: Aireon.

The first real-time worldwide air traffic surveillance system

There has never been worldwide surveillance of air traffic until now. Large areas over the Atlantic and the Pacific Ocean has been un-surveilled.

In fact, 70 percent of the air traffic over the Globe relied on the aircraft reporting their positions to air traffic control with 10 to 15 minutes intervals for traffic control and separation.

This has forced large separation distances and the organization of the air traffic in in-efficient air corridors for these areas, where aircraft can’t overtake when faster or change altitude when needed to optimize fuel consumption.

We were lastly reminded of the large un-surveilled areas of the World when Malasia Air MH370 went missing without anyone knowing where it went.

ADS-B (Automatic Dependent Surveillance Broadcast), the system where all aircraft send out their position, altitude and speed each second, will be mandatory for practically all aircraft in US Airspace within eight months. This means each aircraft reports where it is and where it’s going every second, for any who wants to know.

But the systems receiving these signals for Air Traffic Control have so far been ground-based. Coverage has been limited by the curvature of earth. Aireon’s space-based ADS-B system now provides real-time air traffic surveillance and tracking of 100 percent of ADS-B equipped aircraft, worldwide.

Don Thoma, Aireon CEO points out what this means: “For the first time in history, we can surveil all ADS-B-equipped aircraft anywhere on earth. Our air transportation system has operated with a safe but less than efficient system in the 70 percent of the world that does not have real-time surveillance.  With the launch of our space-based ADS-B service, Aireon now provides a real-time service which optimizes flight safety and efficiency”

Improved visibility and control over previously un-surveilled airspace—especially across oceanic regions—will allow airlines to fly routes at optimal speeds and levels. An analysis conducted by NATS and the International Civil Aviation Organization (ICAO) has concluded this will deliver cost savings of up to US$300 per transatlantic flight, plus reducing carbon dioxide emissions by two tonnes per flight.

“To know the position, speed and altitude of every ADS-B equipped aircraft in oceanic airspace – in real-time – is a transformational change to how our controllers manage air traffic,” said Neil Wilson, president and CEO of NAV CANADA. “The separation can be cut from 40nm to 14nm”.

Martin Rolfe, NATS CEO, said, “The trial in the North Atlantic, the busiest oceanic airspace in the world, with over 500,000 flights every year and a forecasted 800,000 flights per year by 2030, will demonstrate to the entire aviation industry, that global, space-based ADS-B can revolutionize the service that we provide to our customers and the traveling public by transforming the way we perform air traffic management over remote regions.”

How Aireon contributed to the ET302 investigation

As described in our first article about the ET302 crash, FlightRadar24 had limited coverage of the flight path of ET302. Only when Aireon provided the crash investigators with its Sattelite received ADS-B data from the flight could the complete flight trajectory be analyzed with real-time high-quality data.

It could then be seen the ET302 showed the same roller-coaster pitch trajectory for the beginning and end of the flight as Lion Air JT610. This was one key puzzle piece in the the grounding of the 737 MAX.

By Bjorn Fehrm

April 19, 2019, ©. Leeham News: Boeing’s CEO Dennis Muilenburg yesterday flew with the final version of the updated MCAS software on a 737 MAX. It will now enter certification flights, having completed 120 Boeing test flights.

Here my perspective on MCAS and the overall Boeing 737 safety record.

The 737 has a good safety record

The Boeing 737 is flying with more aircraft around the world than any other aircraft type except the Airbus A320 series. Both have around 7,500 aircraft in service. And both have good safety records.

For the 737, this has been the case over its 50 years of operational service. The type has no special issues, like deep stall or difficult handling or landing characteristics. It’s a vice-free aircraft compared with many other airliners which have operated the skies.

This shall be remembered when one judges whether the 737 MAX will be safe after the updated MCAS is certified and the MAX enters service again. If only the original MCAS implementation had got a 10^th of the attention the now updated function has got. Then we wouldn’t have had two fatal crashes with 346 persons killed.

If the original work with MCAS would have done ONE of the following three things correctly, we wouldn’t have the MAX glued to the ground right now:

• Implemented the function with the care and attention such functions shall have.
• Made a proper Emergency checklist for the system.
• Informed the Pilots of the function and trained them on its fault modes.

Revealing investigation

The many investigations into the MCAS debacle will reveal how all three of the above conditions could be ignored. If any of them had seen proper action,  the accidents wouldn’t have happened.

The introduction of the improved MCAS addresses all three of the conditions, and by it, should ensure we won’t have any more MCAS-related accidents. The 737 MAX can return to be a backbone of our air transportation system. The attention shall make MCAS a problem of the past.

One now ask what else could have fallen victim in the race against the Airbus A320neo? Was any other area of the 737 MAX glossed over like MCAS? Here the ongoing investigations and Boeing’s own soul searching shall make sure anything else which is not a 100% job will be addressed. Will this happen?

We tend to forget issues with our airliners are detected on a daily basis and get fixed by the established system. Our high level of air traffic safety comes from this daily work.

There is a stream of ADs (Airworthiness Directives) from the authorities and SBs (Service Bulletins) from the OEMs which correct and improve our aircraft.  The 737 included and this type has not had more issues than any other type. Its track record over the 50 years is good.

If the race against the A320neo caused any other non-perfect MAX solutions to be introduced, Boeing should focus on fixing them ASAP. Any more issues with the 737 MAX and the trust in the type will wear thin. The sound 737 base aircraft does not merit such a fate.

Note: Our partner Mentour Pilot has released a video showing the effect of a miss-trimmed elevator when manually trimming a 737, worth a look. It’s here.

By Bjorn Fehrm

April 26, 2019, ©. Leeham News: In the wake of the 737 MAX crashes the standards to which Boeing and the FAA qualified and approved the 737 MAX MCAS function is questioned.

FAA has called the world’s aviation regulators to a meeting on the 23^rd of May to discuss how the revised MCAS function will be approved. But it’s time to discuss more than how the updated MCAS shall pass.

What needs to change: the Pilots or the Aircraft?

I wrote in a previous Corner “we have over 200,000 pilots flying our airliners around the world“. This figure was wrong, we dug deeper and there are more than 300,000 pilots flying our airliners today and there will be more tomorrow.

As the world’s airline traffic increases and reaches new markets, there is a shortage of pilots to fly all the airplanes. Pilots are recruited from all the world’s corners with different backgrounds and brought to proficiency through different training systems.

Given the vast number of operational pilots and new recruits, how practical are the outcries from the Old Garde stating “The crashes show we need better pilots with better training“? Is this the practical fix?

Isn’t it easier and safer to safeguard six departments (the flight safety departments of Boeing, Airbus, Embraer, Bombardier, ATR and United Aircraft) and their oversight authorities, which qualify our airliners for safe flight, are having standards which are high enough? And that these realize what standard to qualify to for these 300,000?

To think the solution is to screen and retrain 300,000 pilots is not living with the present. The worldwide airline industry has changed and it’s not changing back.  It’s more straightforward to change the acceptance level for what we can expose the pilot’s to in an emergency than change those 300,000.

Here’s a case in point.

The wrong checklist

The implementers and oversight of MCAS convinced themselves a miss-functioning system already had an emergency checklist: Trim Runaway.

The Trim Runaway checklist was conceived after several accidents where the pitch trim got stuck in an on-position, either nose up or nose down. Pilots get trained on how to recognize this condition in their yearly recurrent simulator training and what to do about it.

As the trim runs continuously in one direction the checklist prescribes “hit the cut-out” without further ado. The continuous trim in one direction is unlike anything the aircraft normally does, so it’s easy to identify, and once identified time is pressing.

This doesn’t fit at all for MCAS. As Boeing’s Vice President of Product Development and Product Strategy, Mike Sinnett, said when presenting the MCAS fix last month “MCAS is part of Speed Trim System”. Now, Speed Trim System is active every 737 takeoff and every 737 approach. It behaves in very much the same way as MCAS but triggers by Speed change, not Angle of Attack.

In fact, Speed Trim is so similar to MCAS none of the pilots for Lion Air JT043 or JT601 could see or feel the difference. So to rely on a checklist and training for something totally different is just not good enough. Not when 300,000 pilots need to play Sherlock while flying hundreds of passengers and connect a variant of Speed Trim which is dangerous with a checklist which has little to do with Speed Trim.

Further, MCAS can be countered by manual trim, a trim runaway many times not (if the fault is downstream of the opposite force Yoke column cutouts). So an MCAS emergency checklist shall stress how to separate it from Speed Trim and how to trim to neutral stick force while keeping speed in check and then hit trim cutout.

My focus is not the correct MCAS checklist, it’s to have the standards for the safety work where a substandard solution to a problem, relying on an existing, non-suitable emergency procedure to be “good enough”, is not good enough.

Because we design and certify our airliners for a pilot workforce which will soon hit 500,000. And the product and the procedures around the product must adapt to this reality. The days of the old airline industry are gone.

We have entered the mass transportation market and the industry and its players must adapt. And it’s easier to adapt the tools for this transport then how hundreds-of-thousands of individuals shall behave.

By Bjorn Fehrm

May 06, 2019, ©. Leeham News: Bombardier’s CEO, Alain Bellemare announced yesterday the company will streamline to a Train and Business jet company.

This means there is no longer place for a Commercial aircraft division nor its Aerostructures parts in Belfast and Morocco serving these aircraft.

Figure 1. The CSeries/A220 Carbon Fiber Reinforced Polymer (CFRP) wing. Source: Bombardier.

Belfast technology can bring needed cash to Bombardier

Bombardier is a debt-laden company. The CSeries development together with Global 7500 and Learjet 85 loaded Bombardier’s balance sheet with nine billion dollars in debt. There is since years a high priority to lower this debt level while focusing the company on Trains and Business Jets.

The Belfast facility’s key activity is doing wings for Airbus A220 aircraft. It also does nacelles and has won a future nacelle program for Airbus A320neo aircraft with Pratt & Whitney engines. Belfast also does fuselage sections for Bombardier’s Business Jets but this is of a lesser scale than the Airbus engagement.

A unique composite wing

The wing for the A220 is made with a unique Resin Transfer Injection (RTI) process which is ideally suited for manufacturing wing structures in the size and quantities needed for the A220 series.

It combines a manual dry Carbon fiber mat layup with an injection of the Epoxy resin when the fibers, laid on the wing skin’s female mold, have been bagged and placed in an Autoclave. The wing skins produced are then entering the autoclave a second time adding additional mat layers and the wing’s stringers. The additional parts are then co-cured to the wing skins. The result is CFRP wing skins of high quality produced at a very competitive cost level.

This technology is the Crown Jewel of the Belfast operation and Bombardier assumes it can get Airbus or one of Airbus aerostructures partners to pay top dollars to get hold of this asset. With Airbus expanding the reach of the A220, there is a long term future for the Belfast Carbon Fiber Reinforced Polymer (CFRP) wing technology.

I would think Airbus would like to restrict the technology to only Airbus projects. This would speak for an Airbus purchase of the asset. Why hasn’t then this happened already? Airbus and Bombardier are partners in the A220 program?

We must assume Bellmare wants more than Airbus has offered to pay. By opening up to competition he hopes more debt can be paid off by selling to the highest bidder.

Why is the Belfast wing process so interesting?

If acquired by one of the tier-one aerostructure players like Spirit Aerosystems or GKN, the technology could be used for other aircraft programs than Airbus A220.

The Belfast developed technology produces a composite wing to an attractive price with rather modest investments in tooling infrastructure. There is no need for Automated Fiber Placement (AFP) machines costing tens of millions dollars for laying down hundreds of layers of pre-impregnated tape (Prepreg), before cooking the lot in the autoclave to a wing skin or wing spar.

The Belfast process in manual in its layup of precut mats but tape laying of prepreg tape is also largely manual today. After each automated tape laying layer (and there are hundreds in a wing skin) the whole surface must be manually inspected and any faults corrected. It’s a process which takes as long as the laying of the tape for the layer. In the Belfast process, the persons laying down the mats do this inspection concurrently with extending the fiber cloth.

The Belfast process is the present lowest cost process for doing a CFRP wing of high quality. The Russian AeroComposit process with Resin Infusion of Dry Fiber which is cured in ovens promises even lower cost. But the lack of the compacting and gas evacuating high pressure of the autoclave makes the quality level and by it, the strength to weight ratio, an unknown.

Only Russia’s United Aircraft knows the answer and with western sanctions hitting its western sourced production materials, it will most likely be tight-lipped with how it’s Russian dry Carbon fibers and Epoxy resins perform.

By Bjorn Fehrm

May 10, 2019, ©. Leeham News: An Aeroflot Sukhoi Superjet 100 crash-landed Sunday at Moscow Sheremetyevo Airport and burst into flames.

We shall look closer at the likely cause of the accident, which involves the SSJ100 Fly-By-Wire (FBW) control system working in Direct law.

The SSJ100 involved in the accident. Source: Wikipedia.

Flight Aeroflot 1492 to Murmansk

The flight, Aeroflot 1492, started from Sheremetyevo for a flight of two hours to Murmansk, 800nm away. During climb out the aircraft was hit by lightning at 6,900ft and leveled off at FL100.

Normally an airliner recovers after a short hiccup after a lightning strike, but this time the aircraft’s radios and autopilot would not function after the strike. The crew, therefore, turned back to land on the runway they departed, Runway 24 at Sheremetyevo airport.

As the crew had intermittent radio contact with ATC on the emergency frequency 121.5 MHz (probably over the standby radio) they decided against long time circling over Moscow to dump fuel due to the heavy traffic in the area.

Instead, they prepared to land with an aircraft which was over Max Landing Weight but not more than a couple of tonnes. In normal landings, this creates no problems on runways the length of Sheremetyevo’s runways (shortest runway of three is 10,500ft, longest 11,650ft).

Direct law makes the aircraft more difficult to fly

The lightning strike had put the FBW in its backup mode, Direct law. This is an emergency mode which bypasses the aircraft’s flight law computers and controls the aircraft’s control surfaces directly. One can say the aircraft is controlled by electrical wire instead of steel wire.

A FBW aircraft like the SSJ100 has a sophisticated digital feedback based FBW. This means the Pilot commands the aircraft movements he wants by sidestick and pedals. The FBW computers then move the aircraft’s control surfaces to achieve the commanded movement.

If the Pilot commands a pitch up to flare during landing, the aircraft pitches up at an adapted rate for the flare situation which is the same regardless of center of gravity or flap setting. The aircraft is nice and predictable to fly.

When such a system is forced to backup mode, Direct Law, in this case by a lightning strike, the aircraft becomes more difficult to fly. The movements of the sidestick and pedals are now moving the control surfaces directly. There is no damping nor any adaptation of stick sensitivity to different flight phases.

Full deflection of the stick must command full deflection of the control surfaces in case it’s needed to control the aircraft. This makes for a sensitive stick when making the small corrections needed for normal flight. Large movements of the stick and the aircraft can run into a Pilot Induced Oscillation, PIO.

Having watched the video of the landing I guess this is what happened. The Crew conducts an ILS approach on RWY 24 (the Nav receivers worked apparently). As they approach the runway the Pilot prepares to flare the aircraft.

The aircraft is about 15 to 20 knots over normal landing speed according to FlightRadar24 traces, which is plausible. They are overweight, on backup systems and might even be on backup instruments. A padding of the approach speed when landing overweight on a long runway is then natural.

As we only have video when the aircraft has started the flare over the runway it’s difficult to say if the PIO had started on short final. I would not be surprised if it had. When one sees landings with a runway gallop like for the SSJ, the PIO normally start before the runway threshold, on short final when the Pilot starts the flare.

Either he flares too little or too much initially. In both cases, he must correct and now he is stressed. His feel is, the aircraft is not responding to his commands. This pumps adrenalin into the muscles which get stiff. Stiff muscles increase the PIO and the over corrections further.

The gallop gets worse and worse until at the third touchdown the main landing gears, attached to the rear spars, ruptures the wingbox and with it the wing’s fuel tanks. Now fuel sprays out into the engine exhaust and the rear of the wing and fuselage is quickly engulfed in flames. The catastrophe is a fact and 41 of 78 onboard the aircraft perish in the smoke and flames.

I refrain from commenting on the evacuation with all its facets, I want to focus on why the aircraft burst in flames. One can talk of Pilot error but there are reasons for what happened. Direct mode is a certified flight control mode but it’s not certified to the same standards as full FBW mode.

By Bjorn Fehrm

May 18, 2019, ©. Leeham News: We are now two months into the grounding of the Boeing 737 MAX because of MCAS. Boeing announced yesterday it has finished the work on the fix and it’s now ready for FAA certification flights. Once FAA has certified the fix, the 737 MAX will return to the sky. At least this is how it used to be.

A lot of hesitation and distrust has come into the system since the March 13^th grounding. Here’s why I wouldn’t hesitate to fly on the MAX after the fix.

The critical question

I think most pilots and aviation experts trust Boeing to get MCAS right the second time around. I do. The updated implementation has all the precautions, deliberations and global limitations the first version should have had.

In fact, the update is the glaring evidence of the initial MCAS’s deficiency and carelessness in its implementation. As thorough the fix is in all its aspects, as negligent was the first try.

Now a person of logic says: “If Boeing was as negligent in the development of the 737 MAX to let MCAS slip through, what else is in there?”

Here I rely on the Boeing CEO and top management to have realized the Boeing airliner which pays the bills can’t fail. If there’s one more blip, Boeing will not only be shaken, it will be down for counting.

I expect the top management to have put the question to its MAX team:

“If there’s anything else in the MAX you don’t feel 100% confident about, just tell us. We’ll fix it, no matter what.”

“This time, there’s no pressure,” the engineers would have been told. “You will crash your career if you don’t speak.” Before, it was the reverse.

I rely on this question being put and any answers finding its way into the fix. A 737 flight control software update is not a local patch of a software corner. It’s a global update of the system and any cleanups will ride along. Any such cleanups have been flying on the MCAS test flights for more hours than any cleanups before.

No question, no mercy

If the above question hasn’t been put after the crashes and grounding, I have no mercy. Then the top management of Boeing shall all be fired. Everyone. And it should hit the board as well.

I’m so convinced, having been in the mix myself, the question has been put, any answer put forward and any additional fixes implemented so I wouldn’t hesitate to fly on the MAX after the grounding.

By Bjorn Fehrm

May 24, 2019, ©. Leeham News: “Stop dreaming, Start making” was the angle of Airbus responsible for Urban Air Mobility (UAM), Eduardo Dominguez Puerta, presenting during Airbus Innovation days in Toulouse this week.

He also said, over 90% of the present UAM projects will not make it into a certified operational platform. Here’s why.

Figure 1. The motivation for Urban Air Mobility is strong. Source: Airbus.

The motivation is there, but not the rules

Puerta said the motivation for Urban Air Mobility is there, Figure 1. It will start off as a service for the wealthy, then migrate to the masses. This is how most new ways of transportation have progressed.

While there will be a lot of skills needed to achieve a functioning eco-system, Figure 3, having all the function blocks in place for a viable Urban Air Mobility system is not the main hurdle for the projects.

Figure 3. The necessary components for a functioning Urban Air Mobility ecosystem. Source: Airbus.

Certification is.

Urban Air Mobility is about transporting people over the heads of other people. It will only be allowed with absolute safety. And certifying a vehicle to this absolute safety requires the certification rules which stipulates what must be achieved. For the propulsion system. For the navigation system. For the automated flight.

But these regulations do not exist. In fact, they are not even in the making. First discussions have started, but not more.

Airbus has two flying UAMs, the Vahana (Silicon Valley, Figure 4) and CityAirbus (Airbus Helicopter at Donauworth Germany, Figure 5).

Figure 4. The Vahana demonstrator. Source: Airbus.

Figure 5. The CityAirbus demonstrator. Source: Airbus.

Neither of these will make it to a certified vehicle says Puerta. As there are no certification rules, they couldn’t be designed to be certifiable. They are demonstrators, as are all the other Urban Air Mobility vehicles. And this is what will kill most projects.

When investor learns their spent money has not brought them close to a practical system, and this requires a long wait for rules, followed by design, production and certification of a different vehicle, they will stop. Only a few projects will make it through to certification when the rules will finally be there, says Puerta.

Certification rules are the work ahead, not further vehicles

Puerta said Airbus will not invest in further vehicle projects until certification rules are there. And to get these rules requires Airbus to engage with its competitors to help authorities create these rules.

This is now the top priority, not further flying vehicles, as they don’t bring Airbus closer to the goal, a functioning Urban Air Mobility system.

Bjorn’s Corner

May 31, 2019, ©. Leeham News: Last week the new Airbus CTO, Grazia Vittadini, said we should not expect electric aircraft anytime soon when presenting at Airbus Innovation days. What is realistic is hybrid developments, not battery-based designs.

After having made the basic checks about Electric aircraft in my Corner series 18 months ago, this was music to my ears. Finally, someone was curbing expectations.

Figure 1. The Gartner technology hype curve. We are somewhere in the first peak.  Source: Gartner.

Battery-based aircraft is a near impossibility, hybrids are difficult

Vittadini’s team had made the sums. Battery driven aircraft is a near impossibility. Since doing my check on the efficiency of different electric aircraft, all I have learned in the 18 months since the series is making the equation worse.

I wrote batteries are 40 times heavier per energy unit (kWh/kg) than Jet fuel. A more correct figure would be 100 times. Battery systems designed for the first electric aircraft have a systems level energy specific weight of 0.12 kWh/kg and jet fuel is at 12kWh/kg. The battery systems might improve to 0.30kWh/kg over the next decade but not more. Not for certifiable battery systems. This is what Vittadini’s team told me.

The 100 times increase in weight for the energy is devastating but the full story is worse. If we start a flight of a jet fuel aircraft at say MTOW (Maximum TakeOff Weight), we would land the aircraft with around 20% lower weight as jet fuel gets consumed during the trip. For a battery-driven aircraft we takeoff at MTOW, fly the route at MTOW and land at MTOW. This worsens the efficiency of the electric aircraft further.

An electric aircraft has larger freedom of positioning its propulsors on the aircraft, Figure 2. But it can’t make up for the energy density problem, it brings at most a 20-30% improved efficiency.

Figure 2. Airbus concept for Boundary layer ingestion propulsors. Source: Airbus.

It means we have now a drag improvement of 30% compared with a 10,000% efficiency loss on the fuel side. Over the next decade, it improves to a loss of 4,000%. We don’t even have to calculate the aircraft weight and by it, the induced drag of a battery based electric airliner, to understand it’s a non-starter. Today, tomorrow and after tomorrow.

Hybrids are difficult

Vittadini also talked about electrical hybrids, with the BAe146 based E-FanX project with Siemens and Rolls-Royce as an example. She said it was a project to learn from. To learn about transferring 2MW (MegaWatts) at altitude over a 3,000V conduction chain. To learn how a 2MW battery can be designed and work safely in an aircraft.

The sizing of the battery is one of the problems. If the battery shall give 2MW during one hour it will weigh 20 tonnes, which is not possible. The Bae146 has a maximum payload of 11 tonnes.

With crew, test equipment and other items on board, there might be 5 tonnes left for the battery. It would then last 15 minutes when feeding a 2MW propulsor.

By the above, we realize an airliner hybrid is a gasturbine based system with a minimal battery for starting the gasturbine and as a backup in case of an engine or generator problem.

But we still have the challenge to explain why a Gasturbine-Generator-Conductor-Converter-Motor-Fan is more efficient than a Gasturbine-Fan combination. At each step in the hybrid chain, we lose a minimum 2%, most times 5% in efficiency.

The Gasturbine-Fan skips the complexity, efficiency losses and weight/volume of the Generator-Conductor-Converter-Motor complex. No-one could explain to me the elegance of the more complex and heavier system, at least not over the last 18 months.

Hype curve dynamics

After the euphoria of the first peak of the Hype curve, Figure 1, comes the ride down to the Through of Disillusionment. To me, we are now starting this downward ride.

Many projects are still born with inflated expectations, seeking to be the Tesla of the skies. The Corner series about Electric aircraft explains why we don’t have a Tesla situation for airliners. The Sky lacks stop lights.

But the first signs of a more realistic approach are there. Airbus’ innovation team tempers the expectations for the first time. We will see more of this going forward.

By Bjorn Fehrm

June 5, 2019, © Leeham News.: The Air Current broke the news earlier today Mitsubishi Heavy Industries (MHI) is negotiating with Bombardier to buy the CRJ program.

BBC has got comments from both companies confirming the discussions, with cautions nothing is settled and it can still result in a no deal. Should it happen it would make a lot of sense for both parties.

UPDATE: Bombardier has issued a statement confirming the discussions, see below.

Benefits to Mitsubishi from acquiring the CRJ Program

The immediate benefit to Mitsubishi would be its regional jet enterprise, Mitsubishi Aircraft Corporation (MITAC), would go to a 45% market share in the all-important US market in one go, Figure 1.

Figure 1. In service E-Jets and CRJ700/900 in the US market. Source: Ascend

We excluded the smaller CRJ100/200 and ERJ135/140/145 from the count in Figure 1. Those included, the market shares stay the same with 45% for all CRJs and 55% for the ERJs/E-Jets.

Worldwide the picture would be 37% in-service CRJs (1385 CRJs) versus 63% ERJs/E-Jets (2320 jets).

This brings MHI and MITAC from an outsider competitor to one of two major players with 1300 operator’s world-wide, operating a worldwide fleet of 1385 aircraft.

One would assume the complete organization around the CRJs would be part of the deal. This would bring MITAC and the MRJ or SpaceJet as the new name is rumored to be:

• A 37% Worldwide market share of 1,385 aircraft with 1,385 operators with a US share of 45%. All these operators would need new aircraft over the next 20 years. The SpaceJet would be ideally placed to compete for this business, not as an outsider but as the incumbent supplier.
• The CRJs and SpaceJets would benefit from an established Worldwide support network with over 30 CRJ offices/partners.
• The Bombardier CRJ team is the most experienced Regional jet team in the market, from sales through to production and aftermarket support. MITAC and their customers would benefit from this experience and the CRJ team would get a new future-oriented product to sell and support.

We will see if the transaction will close. If it does it makes a lot of sense for MITAC and for the people inside Bombardier who today work with the CRJ.

The rumor says the SpaceJet will be the only Scope clause compliant jet with the Pratt & Whitney GTF engine and a three-class 76 seat cabin. This catapults the Mitsubishi Regional Jet program from a questionable competitor to the only alternative with new generation engines. Paired with the CRJ it would bring the jet market below 100 seats to two able competitors instead of just Embraer/Boeing Brazil.

UPDATE:
Bombardier Statement on CRJ Program
June 5, 2019 Montréal
Bombardier Inc., Other News
Bombardier has recently stated it would explore strategic options for the CRJ Program. From time to time, this may lead to discussions with potential counterparties. While Bombardier does not generally comment publicly on market speculation or rumors, in light of recent media reports, Bombardier believes it is prudent to advise stakeholders that it is in discussions with Mitsubishi Heavy Industries, Ltd. with respect to its CRJ Program. We will not further comment on the nature of the discussions. Before any agreement can be reached further review and analysis by Bombardier management and approval by Bombardier’s Board of Directors are required, and Mitsubishi Heavy Industries, Ltd. must complete its due diligence review and own analysis and approval process, which are outside of Bombardier’s control. There can be no assurance that any such discussions will ultimately lead to an agreement.

By Bjorn Fehrm

June 6, 2019, ©. Leeham News: In last week’s Corner I wrote: “The reason electric cars work and airliners don’t is the Sky lacks Stoplights“.

The discussion was part of my previous series on Electric aircraft, but it was in the comment section. Here is a more exhaustive run through of the main reasons.

Figure 1. The Tesla electric car which is a functioning replacement for a combustion engine car. Source: Tesla.

The difference between car driving and airliner operation

The key reason electric cars with a battery energy source work and airliners don’t is that the normal car is an energy hog in our daily use and it’s less sensitive to weight.

Accelerating and coasting/stopping

Car: We burn energy when accelerating the car from a standstill after every stop, be it for stop lights or traffic jams. Then after a while, we brake the car to a lower speed or to a stop with our friction brakes, wasting the energy we used to get to speed. It repeats over and over again.

The electric car recovers the built-up motion energy when slowing down, by it making it less wasteful with energy than the normal car.

Airliner: The airliner accelerates once from standstill on the runway to takeoff speed and then gradually to cruise speed during the climb. When descending the investment in potential energy during the climb is recovered. It overcomes the drag during the descent.

A minimum of energy waste characterizes the airliner operation. All energy is used to overcome drag. The potential energy from cruise height is to a large part recovered during the descent before landing. So there is no energy waste to gain for an electric airliner compared with a combustion one.

Sensitivity to weight

Car: The car is less sensitive to the added weight of batteries than an aircraft.

A normal 1,500kg car when driving at 100km/h (60mph) has a tire rolling resistance of 220N/50lbf and an aerodynamic drag of 220N/50lbf. If we substitute the fuel with the typical Tesla battery pack of 65kWh the car weighs 2,000kg. Drag stays the same with tire rolling resistance due to weight now at 294N/66lbf.

Aircraft: If we take a similar loaded weight aircraft, like the Cessna 206 with five passengers, drag due to weight (induced drag) is 440N at 100kts. If we substitute fuel for a Tesla 480kg battery pack the induced drag increases to 780N. The substituted fuel has an energy content of 2,600 kWh whereas the pack has 65kWh but we use the pack weight of 480kg  to make the weight increase comparable.

Summary

Electric cars can recover the wasteful brake energy lost if many situations. They can, therefore, successfully compete with our energy wasting combustion cars.

There is little energy waste in a modern airliner’s operation. Electric airliners, therefore, have no energy waste to recover.

The drag increase due to weight for the Car is 33% when going from combustion to electric. The airliner’s drag due to weight, induced drag, increases with 78% when we convert our aircraft to electric with the Tesla battery pack. As noted we would cut range to a fraction of the fuel based aircraft. We need a much larger battery pack to keep range, making the induced drag increase much larger (induced drag scales to weight squared).

Aircraft are very sensitive to weight, cars are not. Weight is the aircraft designers arch enemy. This is ignored/forgotten by those proposing battery based transport aircraft.

By Bjorn Fehrm

June 13, 2019, © Leeham News.: Mitsubishi Aircraft Corp (MITAC) has done more than a rebranding and new livery in creating the SpaceJet out of the MRJ70.

It’s changing the design, its materials and several parts of the interior to accommodate more passengers than the MRJ70.

• Related story: How the SpaceJet came to be.

Here is a technical analysis of the aircraft, based on information released today and our own Aircraft Performance Model.

We describe the changes MITAC made to the MRJ70 to end up with the M100 SpaceJet and what these mean for passengers and operators.

Figure 1. The Mitsubishi M100 SpaceJet replacing the MRJ70. Source: Mitsubishi.

The problem with space

Mitsubishi focused on space efficiency when transforming the MRJ70 to the M100. The all-important US Scope Clause market requires premium seating space for the passengers but doesn’t allow enough gross weight to achieve it with the new generation, heavier engine. The MRJ90 (and the Embraer E175-E2) were designed in anticipation that the Scope Clause would be relaxed. The two airplanes are too heavy under the Scope Clauses.

The MRJ70 carried fewer passengers in its design than needed: 69 vs 76 in the typical US configuration, a major economic disadvantage.

With the MRJ90 not Scope-compliant (it works outside the US), MITAC turned to improving the MRJ70. This morphed into the M100 SpaceJet.

There are several restrictions for this market depending on which mainline carrier the feeder service is performed for. The most prevailing are:

• A maximum of 76 seats for outsourced operations. There are several seat buckets with numbers of allowed aircraft by seat bucket and agreement, but the 76 seat bucket is common to the three mainline US Carriers and the largest bucket.
• A Maximum TakeOff Weight (MTOW) of 86,000lb/39t, also common between the three mainline US Carriers Scope agreements with their Pilot unions.

These two restrictions create a weight dilemma for the aircraft OEMs. The outsourced feeder services for the mainline shall ideally have the same cabin classes and comfort as the mainlines’ single-aisle domestic operations.

As these cabins have evolved into three classes with Domestic First Class, Premium Economy and Economy, the required cabin size for the Scope aircraft has increased.

For the Bombardier CRJ900, the length of the cabin is no problem, but the width is. Its cross-section makes for a hunkered down boarding experience and cramped seating. The latest ATMOSPHERE cabin design helps but it can’t change physics.

The Embraer E-Jet has a wide enough cross-section to offer a good boarding and seating experience and its cabin length for the Scope-compliant E175 is adequate but not more. Embraer, therefore, increased the length of the E175-E2 to give airlines more freedom with the cabin layout.

This ran the E175-E2 into a weight problem. The longer aircraft with the new heavier Pratt & Whitney 56 inch GTF engines is too heavy for the 86,000lb limit. With passengers loaded, it only allows fuel for 950nm sectors, too short for the operators. There are, therefore, no firm orders for the type from US carriers.

The MRJ70 was light enough to have an adequate range when operating under the 86,000lb Scope limit, even with the new Pratt & Whitney 56-inch GTF engines. And it had the same cross-section as the E175, so boarding and seating comfort were fine. But its cabin was too short. In a three-class layout, the seating went south of 70 seats.

Enter the SpaceJet

How did Mitsubishi solve the space and weight problem? Here our analysis, based on the released information.

The length of the aircraft was increased with 1.1m, to 34.5m, Figure 1. At the same time, the cabin length was increased with 1.6m or two seat rows with windows, Figure 2.

Figure 2. Cabin layouts of the M100 SpaceJet. Source: Mitsubishi.

This gives the same cabin the length as the E175 but with a more flexible front end. The E175 has a front galley service door which is placed forward of the galley. This puts the galley with its hard wall between the entrance area and the cabin. Head injury concerns then put the first seat row away from this wall.

The M100 cabin has the service door aft of the galley and it allows airlines the flexibility to plan the front of the cabin as they prefer. One can place seats close to the entrance and service doors for maximum capacity or place closets there for passenger coats, all depending on cabin layout preference.

The other optimized area is the use of the aircraft’s cross section. Figure 3 shows the E175 cross-section compared with the M100 cross-section.

Figure 3. The E175-E2 cabin cross-section on the left and the M100 cabin on the right. Source: Leeham Co and Embraer/MITAC. Click to see details.

The E175 and M100 share almost identical cabin cross sections with the M100 being 2cm (0.8 inches) wider and higher.

Figure 3 is a hybrid, as we have combined the E175 cross-section with the wheels first bins from the E175-E2. The in-market E175 has “wheels to the side” bins which are shallower, as was the MRJ70. This restricts the carry-on luggage for the E175, essentially offering every second passenger space for carry-on bags.

The new wheels first bins for the M100 offers every passenger carry-on bag bin space. So it wins over the E1 hands down. But this would be to easy a comparison.

Embraer could upgrade the E175 cabin to the E175-E2 standard while waiting for Scope release. So we decided to compare the M100 to such a configuration to find any differences.

The 2cm (0.8 inches) wider and higher cabin together with an 18-inch aisle allows 18.5-inch seats for the M100. The narrower E175 has 18.2-inch seats with a 19-inch aisle.

Ignore the difference in seating depiction style in Figure 3. The E175 is from a drawing in Embraer’s Airport planning guide; the M100 is from the SpaceJet brochure. The key is the measurements and the perceived space around the shoulder/head area for the depicted 6ft 2in passenger.

The important difference is the form of the bins. The E2 bins are fixed. They must, therefore, be canted down a bit to allow the ingress and egress of the bags.

The SpaceJet team went for pivot bins. It allows the bags to snug up against the cabin wall when shut. This gives a climbing bin profile when shut like the Boeing Sky Interior. The wheels first pivot bins and the profile of the shut bins are visible in Figure 4.

Figure 4. The new wheels first pivot bins which form a concave upward slope when shut. Source: Mitsubishi.There will be a cabin mockup at the Paris Air Show next week and we will check out the feeling the new bins create. If they create the feeling of space the Boeing Sky Interior gives, the SpaceJet team has succeeded.  We prefer the Sky Interior to all other single-aisle interiors.

The M100 is also offered with the latest cabin amenities. Operators can specify seat USB C charging, in-seat IFE and Ku/Ka-band satellite-based WiFi.

The M100 has repositioned the rear galley/lavatory rearwards, increasing the space for the cabin and decreasing a baggage compartment which was sized for a time when passengers checked their luggage.

With the new bins, the 480sqft baggage compartment, down from 640sqft, will be mostly empty. This gives an opportunity for cargo, as the loading door is large and the compartment has a workable height.

The rear lavatory is now placed more centrally, making it less cramped and easing ingress and egress for wheelchair passengers.

The weight trick

So how can Mitsubishi get a three-class cabin into a Scope-compliant aircraft with Pratt & Whitney GTF engines when Embraer can’t?

First, the M100 is a more snug fit around the 76 seat cabin than the E175-E2. Assuming the weight limit would be gone, Embraer increased the length of the E175-E2 by one window row on top of the E175. It also put a wider wing on the aircraft, to fly further. The wing is 2.3m wider than the E175 and 3.2m wider than the M100 wing.

The width gives range if you are not Take Off Weight (TOW) limited. With Scope, you are. Low empty weight is then more important than wingspan as span drives wing bending moment which drives weight.

If you don’t have a large enough empty weight to MTOW margin, you can’t fill the tanks when the passengers are on board. The E175-E2 can only fill 4t of fuel when its Scope cabin is full. This gives an operational range of 950nm, too short for the operators.

To get a low empty weight, Mitsubishi uses Aluminum-Lithium alloys and Carbon Fiber Reinforced Polymers (CFRP) for more parts than on the MRJ90. This is combined with smaller winglets to cut the wing bending moment to save further weight.

The result is the M100 can carry 50% more fuel than the E175-E2 when flying with 76 passengers, enabling a range of ~1,500nm.

For an international market, the MTOW is free. Here the M100 42t MTOW gives a 1910nm range with a single class 84 seat cabin filled with passengers.

Summary

The MRJ90 was too large and the 70 too small for the largest part of the market, the operators in the US flying under Scope Clause restrictions.

The M100 SpaceJet is a major makeover of the MRJ70. The target has been an aircraft which can fly 76 passengers in mainline three class comfort on the US feeder routes while using the latest engine technology.

Has Mitsubishi succeeded and is it OK to call the result a SpaceJet?

On paper, it looks good. The range is there as is the space for the passengers.

Is there enough space for a SpaceJet moniker? The E-Jet cabin is the most comfortable cabin in the market for an economy passenger. You are either at an aisle or window and you have plenty of space. The A220 has 18.5-inch seats with the middle seat on the three seat side at 19 inches. But 60% of the seats are three abreast and the bins are less “Sky Interior” than the SpaceJet’s.

The M100 takes the cabin experience one step further than both of those, so we give the SpaceJet name a pass.

By Bjorn Fehrm

June 14, 2019, ©. Leeham News: In last week’s Corner we discussed why aircraft with batteries as an energy source will be short ranged for decades to come. The battery energy density is too low and it won’t change appreciably over time.

Now we look at the challenges hybrid transport aircraft face when competing with today’s turbofan airliners.

The Zunum Hybrid electric airliner. Source; Zunum.

Why hybrid solutions for aircraft is more difficult than for cars.

The CAR: The reason hybrid cars work well is the same as for battery based electric cars. The normal car is an energy hog in our daily driving.

The electric motor driving the wheels in the hybrid car is reversed into a generator when slowing down for a queue or stop light. The hybrid car recovers energy where the normal car doesn’t.

Additionally, the combustion engine in the hybrid car, driving a generator which feeds the electric drive motor and loads the batteries, is also made to run at an optimum speed where its efficiency is at its highest.

A combustion engine driving our normal car through the gearbox is working outside of its best efficiency range a large part of the time.

The Airliner: The difference to an airliner is the gas turbine driving a propeller or fan for our airliners is running at its optimum efficiency for the whole cruise phase. At takeoff, climb and descent it’s running outside of its most efficient RPM but this only constitutes 10% of the mission time.

Another challenge for the hybrid air transport projects is the available gas turbine shaft engines. These are far from the most efficient cores in the market.

A useful proxy for gas turbine core efficiency is its Overall Pressure Ratio, OPR. The values the engine manufacturers give is the highest OPR for an engine. This is typically the top of climb value where the engine is spinning the fastest.

The present highest value for a turbofan is the GEnx-1B76 at 58:1. This value is a bit above the cruise value and in the region where the total efficiency of the core has deteriorated a bit from its maximum, which is at Cruise OPR. But the given OPR from the OEMs is a good proxy for cruise thermal efficiency of the engines. The cruise thermal efficiency for the GEnx-1B76 is 58%.

The OPR for the best turboshaft gas turbine certified for flight is below 20:1 (Ground power station gas turbines can have higher values). Part of it is these are small cores but the small cores for turbofans are above 30:1 today. An example is the Pratt & Whitney 56 inch GTF for the Mitsubishi SpaceJet/Embraer E175-E2. It has a maximum OPR of 32:1 and a cruise thermal efficiency of 50%.

So even without the efficiency losses for the hybrid aircraft from the chain: Gasturbine – Generator – Power Distribution – Inverter – Motor – Fan as opposed to the: Gas turbine – Fan chain for present airliners, we have problems finding available shaft gas turbines which can match the efficiency of today’s turbofan cores.

We will need the development of a new generation of turboshafts based on the best turbofan cores to close the gap in efficiency to the present generation of turbofans.

It will take time

While the development of efficient flight certifiable Generators, Distribution networks, Inverters and Motors is ongoing, a new generation of turboshafts which can match the efficiency of the present cores in our turbofans is not in development or even discussed.

The latest turboshaft is the GE Catalyst and it’s proud of its 16:1 OPR core and its cruise thermal efficiency of 40%.

So the reality is hybrid solutions for aircraft compete with super-efficient turbofan propulsors and even if the hybrid chain can be made efficient (which it is not yet) the gas turbine driving the hybrid chain is not up to snuff. And it will take substantial time and investment to fix this problem.

Summary

The talk of gaining back efficiency in hybrid aircraft by running the turboshaft at a higher efficiency than the turbofans in our airliners is a pipe dream.

The efficiency of the turbofan is at its peak during 90% of the operation (as opposed to the car engine) and the turboshafts available for hybrids are generations behind the turbofan cores in efficiency and sophistication.

By Bjorn Fehrm 

June 18, 2019, ©. Leeham News: Airbus new management team has set the company ambitious targets for the future. These not only describe how to develop and produce new, more competitive airliners but also defines Airbus’ contribution to a sustainable aviation industry, contributing its part in the fight against climate change.

The new Airbus CEO, Guillaume Faury said at the opening of the Paris Air show “We must find a way to decarbonized aviation. This is for our generation to do. It’s expected of us by the flying public and by society”.

Decarbonized aviation

Carbon emission and the burning of fossil fuels are connected to 100%. When fuel is combusted in the engines of our aircraft, each kg of burned fuel produce 3kg of CO2 gas.

“If we don’t do something about the emission of CO2 from our airliners we will double the emission by 2050 as we double the number of aircraft,” said Faury. “We must not double the carbon footprint by 2050, we must half it.

We must support CORSIA, ICAO’s Carbon Offsetting and Reduction Scheme for International Aviation because it’s a global issue and we need to find a global solution for a Carbon offset initiative”.

CORSIA is an international carbon offsetting scheme where international air travel shall be offset, so carbon emissions are flat between 2020 and 2035. This will ensure a carbon-neutral growth of aviation in this period before new technologies and processes can take aviation to the objective of a 50% reduction by 2050.

“We have already done a lot, “ said Faury “We have cut fuel consumption with 80% since the beginning of the jet age. But it’s not enough to reduce fuel consumption at today’s rates. A new generation of decarbonized airplanes must be the target for our developments.

The development in e-aircraft is a step in getting there. There, battery driven aircraft will need to be replaced by aircraft driven by other, more efficient energy sources. The energy density of batteries is simply too low for anything beyond Urban Air Mobility.

When innovating and developing our way to carbon neutral aviation we need to find new fuels which in their creation are carbon neutral. There is no point in having fuels with the high energy density suitable for aviation, like liquid hydrogen when by producing them we create high carbon emissions. Then we have achieved nothing”.

“So it’s not only about the airborne solution. It’s about the whole chain which must be developed for lower carbon emission. This is the goal we must set ourselves” said Faury. “It challenging but at the same time exiting. We must use our technology and innovative power to achieve these goals. This is our real challenge going forward, beyond developing and producing new, more competitive aircraft”.

Faury was careful in his wording, not tying Airbus to any solution like “we will have an all-electric aircraft by XXX”. In subsequent questions and answers, he was well aware of all the challenges for electric aircraft described in my Friday Corners. In fact, we agree on all points and he pointed to alternative ways ahead such as new innovative hybrid solutions not discussed to date or the focus on hydrogen solutions.

“Why would you do the hybrid solutions proposed today, they add complexity, weight with volume and offer no gains?” was his comment. The target is there and it’s an important one. The work to find a solution is also started with Airbus’ Vahanna, CityAirbus and E-Fan X as experiments and learnings on the way. The content of a solution is not clear today, but the need to find one is.

By Bjorn Fehrm

June 28, 2019, ©. Leeham News: “The Federal Aviation Administration has asked The Boeing Company to address, through the software changes to the 737 MAX that the company has been developing for the past eight months, a specific condition of flight, which the planned software changes do not presently address.”

This is the text of an 8-K filing Boeing issued to the stock market two days ago. Here is what it means.

What the 8-K filing means.

Here is what Wiki says about an 8K filing: Form 8-K is a very broad form used to notify investors in United States public companies of specified events that may be important to shareholders or the United States Securities and Exchange Commission.

The filing means FAA has found a flaw in the software Boeing has developed to fix to the MCAS problem. The find and its consequences are significant enough so Boeing’s shareholders should be informed about it. It can affect the value of Boeing on the stock market.

The flaw is not related to MCAS but to how the revised software affects the aircraft’s processors in the Flight Control computers when these have simulated fault conditions.

During a check on how different faults (in this case a fault in one of the microprocessors in the Flight Control computer) can cause Trim Runaway conditions the FAA found the 737 MAX Flight Control computer got overwhelmed by the data flows the simulated fault caused and it delayed the actions the FAA pilot could take to stop the trim runaway.

The FAA pilot classified the resulting pitch change and the delay to stop it as a “catastrophic” event, meaning the plane could crash if this fault would happen in flight.

What does this mean for the MAX?

Boeing must go back and change the updated software for the Flight Control computer so this data flow condition does not occur. The changes will take time and further delay the 737 MAX’s reentry into service. This is why the company did an 8K filing.

The speculation is the changes will add another two months to the delay of 737 MAX reentry into service, meaning the anticipated September reentry now seems optimistic. It also adds to the string of bad news around the 737 MAX.

The discovery is not done in the part of the code which handles MCAS. It’s found as a wider verification the software changes haven’t produced any secondary hazards in the 737 MAX flight control system.

Software changes in a flight control system are always verified with an exhaustive FMEA analysis (Failure Mode and Effects Analysis) and it’s during such verifications the new condition was discovered.

The FMEA analysis lists all possible faults which can occur for a critical function in an aircraft and the fault scenarios are then played through and simulated in the aircraft’s simulators. It was during the simulation of such a possible fault in a 737 MAX simulator at Boeing in Renton the issue was found by the FAA.

It has been questioned why the FMEA performed on the original Flight Control computer software didn’t detect the hazardous MCAS condition caused by a faulty Angle of Attack sensor. If properly executed it should have found how dangerous MCAS could be with certain system faults.

Now, the FMEA analysis worked as it should. It detected a problem, this time caused by how the fixed software changed the data flows in the flight control system’s computers.