A 777 Captain Explains Why Bad Things Happen To Good Airplanes

An interview with Shem Malmquist

Roger Rapoport

On February 20 two uncontained Pratt and Whitney engine failures on Boeing  777 and 747 aircraft made big news in Colorado and the Netherlands. While international coverage focused on shattered engine parts raining down on residential neighborhoods, accident investigators  struggled to understand these events. Unfortunately the aviation safety story behind the broken fan blades causing these explosions appears to be déjà vu all over again.

State of the art engines manufactured by Pratt and Whitney, General Electric and CFM Safran have impressive safety records. Nonetheless, scary engine failures that can damage an aircraft fuselage keep happening  While these events are rarely fatal, they argue strongly for a new and better approach to this continuing air safety challenge. Boeing was quick to back the FAA and the Japan Civil Aviation Bureau’s move to ground Pratt and Whitney PW 4000 powered 777s. 

This decision underscores the evolution of safety management in a high tech industry eager to avoid yet another fleet grounding in the wake of the 737 MAX tragedies. Aviation accident investigator and Florida Institute of Technology Professor Shem Malmquist believes there is considerable room for improved reliability that will make flying safer. An international captain flying 777s (not powered by the Pratt and Whitney engine in question) he offers insights drawn from his new aviation safety book, Grounded. 

Uncontained Pratt and Whitney engine failures on a 777 in Denver and a 747 in the Netherlands took place three hours apart on Saturday. Are you surprised?Malmquist:  Not at all. The regulations require that an uncontained engine failure must be a very rare event. Despite that we would expect some failures.  That’s just how probability works.  Based on this engine’s history it appears that the certification requirement is not being met.  The certification of these engines were based on assumptions that included facets such as the quality of materials, maintenance, inspections, the operating environment, temperatures and how the engines are being used. Would would seem that some of these assumptions are not be accurate. 

Is lack of training an issue?

Malmquist:   It could be, but we don’t know for sure. An NTSB analysis of an uncontained failure on a United 777 bound for Hawaii in February 2018 found that the inspector checking this particular Pratt and Whitney engine didn’t receive the critical training required to do his job.

How is this oversight possible?

Malmquist:  The inspector handling the job had been a Pratt and Whitney employee for over 34 years.  Unfortunately he did not have the necessary thermal acoustic imaging (TAI) process training used to detect internal and external cracking of these PW 4000 hollow core fan blades.

What went wrong?

Malmquist:  In its final report on the uncontained engine failure that hobbled United Flight 1175 in 2018, the NTSB found that the inspector in question “was not able to attend” a “formal training class for the TAI.”

In other words he was too busy doing required inspections on PW 4000 engine fan blades to take the training he needed to do his job right in the first place?

Malmquist:  It’s a little more complicated than that. The National Transportation Safety Board found that: "The fracture of a fan blade due to Pratt and Whitney’s continued classification of the TAI inspection process as a new and emerging technology … permitted them to continue accomplishing the inspection without having to develop a formal, defined initial and recurrent training program or an inspector certification program. The lack of training resulted in the inspector making an incorrect evaluation of an indication that resulted in a blade with a crack being returned to service where it eventually fractured.” This appears to be a gap in the safety controls that should be in place to prevent accidents.

What about the FAA’s role?

Malmquist: This inspector told the NTSB "he could not recall ever seeing an FAA inspector in the shop.” A key component of safety is oversight, and that again seems to be lacking here.

Following the Pratt and Whitney engine failure on the 2018 United 777 flight the manufacturer re-inspected all 9,600 fan blades on these aircraft engines. Was that a step in the right direction? 

Malmquist:  Yes, but as we saw last weekend on the 777 flight taking off from Denver this was inadequate. The Holland 747 flight didn’t have the hollow fan blades found on the 777 but it was another failure of a Pratt and Whitney engine.

Is there a better way to prevent these kinds of uncontained engine failures.

Malmquist:  You need to look at the assumptions underlying their reliability and safety analysis.  By tracking violations of the assumptions you may be able to prevent accidents in the future. It is also important to remember that safety and reliability are two different things. The component failure, in this case, occurred while part of a larger system. The reliability of the fan blades may be great taken in isolation, but appear to be problematic when the entire techno-social system, which includes oversight, is considered.

Could metal fatigue be an issue?

Malmquist:  Of course and that is why we must carefully review the inspection process.  Equally important are the requirements used to insure safety and reliability.  If maintenance is not capturing changes over time it could be that inspections have been relaxed because aircraft appear to be very reliable.  The jackscrew failure that led to the crash of Alaska Airlines 261 in 2000 was mechanical but it was a consequence of standards being relaxed during a time when no related accidents had happened. When there are no failures you might think you can go longer between inspections and reallocate your limited resources to something else.  Relaxing controls led to that accident.

What is the best thing the FAA, Pratt and Whitney and Boeing could do right now to prevent similar uncontained engine failures?

Malmquist:  Before these 777 aircraft are ungrounded Boeing and Pratt and Whitney need to determine, once again, why these unexpected failures keep happening. This means taking another look at all of the assumptions that went in to the engine design and tracking them. They should consider a more robust investigation method such as causal analysis using system theory. They need to take as much time as they need to solve this problem.  Fortunately the current aircraft surplus due to reduced traffic makes this a great time to get that important work done.

Captain Shem Malmquist and Roger Rapoport are coauthors of Grounded: How To Solve the Aviation Crisis (Lexographic Press). They are also coauthors of Angle of Attack on Air France 447. Rapoport is the producer of the award winning feature film Pilot Error.