Ethiopian Airlines Flight 302 crashed shortly after takeoff this week, killing all 157 people onboard and triggering a storm in the aviation industry. The aircraft was a Boeing 737 Max 8—the same type involved when Lion Air Flight 610 plummeted into the sea off Indonesia just five months earlier. Despite similarities between the events, aviation expert Peter Lemme believes they are unrelated.
Both flights seemed to have difficulties maintaining a normal climb, and fell mere minutes after takeoff. It is very rare for two new planes (the Max line, updated versions of the widely used 737 workhorse, only took to the skies in 2016) to experience fatal incidents within such a short time period.
Named as a potential culprit in the Indonesia crash is an automated anti-stalling feature called the Maneuvering Characteristics Augmentation System (MCAS). Boeing gave the Max aircraft larger engines for greater fuel efficiency, and their placement relative to the plane’s center of gravity creates a tendency for the nose to tip upward. MCAS is designed to automatically push the nose back down when this happens, preventing the aircraft from stalling, or losing lift. In the case of the Lion Air flight, experts now suspect an inaccurate sensor triggered MCAS to kick in when the plane was flying normally, causing the nose to repeatedly dip.
But the Ethiopian Air incident may have an entirely different cause. Now that officials have recovered the “black box" flight recorders. Meanwhile many governments, including those of China, Canada, the European Union, and now the U.S. have grounded all 737 Max 8 planes.
Aviation expert Peter Lemme has used data from live flight-tracking service Flightradar24 to study how the Ethiopian Air jet flew in the six minutes before it disappeared from radar. His expertise stems in part from working at Boeing for 16 years in a number of roles, including avionics engineer and thrust management engineer. Since leaving the company he has worked as a technical consultant in the aviation field. Scientific American asked him for his thoughts on what might have contributed to the March 10 crash, and what might be next for the Max 8 line.
[An edited transcript of the interview follows.]
What do we know about the behavior of the 737 Max 8 plane in the Ethiopian Air incident?
On Ethiopian, the airplane got to 1,000 feet. The airplane at that point lost about 400 feet of altitude, which is extraordinary. The next thing that’s interesting is the airplane flew level for about 30 seconds, about 500 to 600 feet above the ground. This is not what an airplane’s supposed to do—you’re supposed to fly away. And the airspeed continued to increase; they got to over 300 knots at under 1,000 feet above the ground. No pilot would consider doing that.
Why they weren’t able to immediately climb in that 30-second period is a mystery. But at the end of it that plane did climb, and it climbed very nicely. We don’t know what happened after that—the last thing we saw was the airplane flying very fast and climbing. One would have thought that whatever happened, they figured it out and off they went. But, tragically, they didn’t.
Does the Ethiopian Air crash share similarities with the Lion Air one?
The Lion Air accident was the result of a relatively minor malfunction in the [MCAS] system. The pilot did not take the appropriate action in a timely manner, which ultimately resulted in him losing control. After the Lion Air accident there was a lot of awareness, so Ethiopian must have been aware of what happened to Lion Air—and it is a really easy error [to correct]. [Editor’s. Note: The investigation into this incident is still underway, and the final report on the findings will not be made public until later this year.]
[The Ethiopian Air crash] does show some interesting features that don’t match up with Lion Air. Normally when you take off, you’re flying without hesitation to maybe 1,000 feet above the ground, and then you push the airplane over a bit and allow it to accelerate. Then you proceed climbing on. But it did not climb out as steeply as it should’ve. So that’s very strange; I don’t know what’s going on there.
What automation is used on the Boeing 737 Max 8, and what purpose does it serve?
MCAS is a very unusual feature because it’s an augmentation: It’s only active when the airplane is being flown manually. Normally you have automatic flight control [only when] the pilot engages the autopilot. In this case they have a system that’s operating somewhat in parallel to the pilot, providing inputs that are in addition to what the pilots themselves are doing.
In the case of the 737 [Max 8] the engines are installed below the center of gravity. And so, as the wing loses lift, the engines generate a pitching movement that causes the nose to want to go up. If the nose is starting to rise all by itself and the pilot doesn’t want that to happen, they will have to push the stick to stop it from going up, and that force reversal is a big no-no. Basically you should pull the stick to go up, and you should push the stick to go down—and you should never have to push the stick forward to stop it from going up. MCAS naturally forces the nose to go down, and that means the pilot continues to be able to pull back.
What do you think about the fact that so many nations have grounded their Boeing 737 Max 8 planes?
I think what’s going on now is because we had China move this way; it has created a cascade more driven by legal handling than good sense. One thing to keep in mind is that when an operator takes an action [under] the guise of safety, anybody else that doesn’t take that action exposes themselves to a certain liability because they had warning and decided to ignore the warning. If something were to happen under those circumstances, they would have enormous legal fallout.
I do not believe the airplane should have been grounded. We know airplanes are going to suffer failures. The idea is that we’ve anticipated these failures, the pilots are trained to handle them, the systems are designed to accommodate them, and off we go. And the 737 Max was perfectly designed with all of those features 100 percent fulfilled.
What’s going to happen to the 737 Max 8 next?
In the case of Lion Air there is action forthcoming: There is a software update. As far as Ethiopian [is concerned], because of the groundings, there is extraordinary pressure now to get to the bottom at least enough to know [what caused the crash].
What we’ll know in the next few weeks will be enough to identify what was the main contributing factor. It could have been an attack, some form of sabotage—can’t rule that out yet. The good news is the flight recorder and the cockpit voice recorder, particularly the voice recorder, would pick up the sound of any explosions.