121pilot, a commercial airline pilot in the USA, has graciously written a three-part series on the history of aircraft groundings. Today, we explore part three, on the current Boeing 737 MAX grounding. Click here for part one on the propellor age and here for part two on the jet age. Today’s post includes the author’s opinion on what went wrong with the Boeing 737 MAX.
The 737 MAX recently became the ninth aircraft type to be grounded after the FAA determined that Ethiopian 302 had likely crashed for the same reasons as Lion Air 601. However, the decision to ground the 737 MAX is quite unique when compared to those before it.
The types that have been grounded previously were grounded in response to the discovery of a serious threat to flight safety like structural failures and fires which could not be addressed through crew action. Because of this, in all of those prior cases, there was a path back to flight. The fact alone that an accident had occurred was not enough of a reason to ground an aircraft. It was only when a specific threat had been identified that the planes were grounded. With a grounding having been based on that threat, the grounding could be lifted once measures had been put in place to address it.
But with the MAX we have a grounding that appears to be based on the crew’s inability to follow standard and well-known procedures to address a specific threat. If the Maneuvering Characteristics Augmentation System (MCAS) activating when it should not renders the MAX unfit for flight, then why wasn’t the 737 MAX grounded after the Lion Air crash? The answer is of course that it does not. Because if the crew follows established procedures for a trim run away (which are a required memory item on the 737) then the system can be immediately overridden.
I think this bears repeating. The issues, potential problems, and failure modes with MCAS on the MAX were all there after the Lion Air crash. Yet, not one regulator or airline believed there was a need to ground the airplane. We don’t have any reason to think this problem is potentially more dangerous or lethal than we did at first. We know that had the Lion Air crew followed established procedures (as the crew of the prior flight on that aircraft did) they could have safely flown the aircraft. If the Ethiopian crash comes down to the same cause (faulty MCAS activation) as Lion Air, then isn’t the accident once again going to be the direct result of a crew that failed to follow proper procedure? Procedures they had just been reminded of and trained on as a result of the Lion Air crash…
It seems based on the totality of the circumstances that the FAA and other regulators grounded the MAX because the public wanted it grounded, not because there was a condition that merited it. The problem this creates is how can you return the aircraft to flight?
MCAS can’t be deactivated because it is absolutely required in order for the aircraft to meet certification standards. The chosen path forward right now seems to be a software fix that will limit how many times MCAS can activate. This software will disable it entirely when the Angle of Attack (AOA) sensors disagree. That’s good and it’s a change that Boeing was working on before the Ethiopian crash. But the possibility remains in the 737 (of all variants) that a malfunction could result in a nose down trim run away.
So as long as the possibility exists of a system running in nose down trim when it shouldn’t, how can you now tell the public it is fixed and safe to fly again? You can’t tell them that possibility is accounted for by the flight crews following an emergency procedure because you’ve already said that wasn’t good enough when you grounded the airplane. Which leaves the FAA and Boeing, assuming that the cause of Ethiopian 302 is the same as Lion Air 601, with a fix that doesn’t address the primary cause of the accident. Because if they share a common cause it is not going to be MCAS or an AOA sensor, but rather pilots who didn’t do what they were supposed to do…