121pilot, a frequent commenter on this blog, is a U.S. commercial airline pilot. I asked him to address the safety of the Boeing 737 MAX and he graciously agreed. His thoughts are below.
There has been a great deal of concern within the aviation community after the recent crash of an Ethiopian 737 MAX, shortly after takeoff. Especially since this is the second fatal crash in five months of this relatively new type of aircraft. Based on the information we currently have, both crashes look eerily similar and leave many people wondering whether the 737 MAX is safe. Nine countries have grounded the MAX and several operators have voluntarily grounded its MAX sub-fleet until they can be assured that it is safe to continue operations.
I’m a professional pilot flying for a US major airline on the Airbus 320 series. While I’m not rated on the 737, like most people in my profession I follow accidents and their causes closely. Personally, I’m not at all concerned with the safety of the 737 MAX at present. Why?
The New York Times published an excellent article last month that looked at the Lion Air crash and its suspected root causes. When Boeing developed the MAX series a new system called the Maneuvering Characteristics Augmentation System (M.C.A.S) was added to the aircraft to meet certification requirements. This system senses the approach of a stall, and forces the nose of the aircraft down to prevent it. It does this through the use of the aircrafts trimmable horizontal stabilizer which along with the elevators controls the pitch (nose up and down) of the aircraft.
The Lion Air pilots faced what is akin to a run-away stabilizer trim scenario. M.C.A.S. reacted to faulty data from the aircraft’s sensors and activated using the horizontal stabilizer trim to force the nose of the aircraft down. While there are procedures to deal with this scenario, at the time of the Lion Air crash training materials on the MAX did not include the existence of M.C.A.S. Nor did they include that one of the methods of overriding the stabilizer trim system on previous models of the 737 no longer worked on the MAX.
I’ve been through run-away trim evolutions in the simulator on prior aircraft that I’ve flown and they are no joke. They can quickly produce control forces that you simply cannot overpower and lead to the loss of the airplane. Which is precisely why we train to deal with them. While M.C.A.S may have been unknown prior to Lion Air it generated enormous attention in the wake of that accident. Consequently, I would expect pilots flying the MAX today to be aware of the system and how to deal with potential faults.
On the Airbus we had something similar happen some time ago when an aircraft experienced an un-commanded nose down pitch movement that the pilots struggled to overcome. In that case, the crew was able to maintain control and land safely but obviously it was a matter of great concern. New procedures were created and we now have a memory item that, should it happen again, allows us to override the computers and regain control of the aircraft.
It’s important to keep in mind that we know very little right now about what caused the Ethiopian crash. The cause may be very similar to the Lion air incident or it may be completely unrelated. But at this point, I see no reason to think that there is a problem with the MAX making it unsafe to fly. Flying transport category jets requires a high degree of professionalism and knowledge of the aircraft systems. The MAX may present challenges that didn’t exist on previous versions but following proper procedures and checklists enables those flying the airplane to do so safely. At this point with the data we have available there is simply no good reason to think the MAX is unsafe.
image: Jeff Hitchcock / Wikimedia Commons