There are several shows I will watch any time I see them, and near the top of the list is “Mayday,” the award-winning Canadian documentary series also known as “Air Crash Investigations.”
Each of the nearly 300 episodes reenacts catastrophic incidents in aviation history and provides insight into what went wrong, how it could have been prevented and what changes the industry made as a result. Circumstances range from hijackings to disgruntled employees, suicides, onboard fires and more. There are collisions, such as the Cerritos Air Disaster (season 4, episode 7) and weather-initiated accidents, such as the wind shear event at Dallas-Fort Worth (season 5, episode 1).
Although these episodes are geared toward a general audience, they also contain lessons for aviation professionals, including aerospace engineers. The root causes of the catastrophic incidents can be grouped into three main categories: mechanical failures, maintenance mistakes and pilot errors. In the end, however, nearly all can be traced back to human choices.
Mechanical failures
Because airplanes are designed with safety as the foremost priority, such failures are quite rare and difficult to predict. Multiple episodes depict a system failure due to fatigue or other degradation and, through reenactments, illustrate how that leaves the crew members fighting for the survival of the aircraft and the lives on board — including their own.
These might seem like straightforward technical issues, but the true root cause can almost always be traced back to a human decision. Consider the “Turning Point” episode from season 11, about the catastrophic failure of a Boeing 747-400’s lower rudder power control module (PCM). A small fracture in the PCM’s metal housing resulted in full-scale deflection of the lower half of the rudder, inducing a violent bank to the left of nearly 40 degrees. Through herculean efforts, the flight crew was able to regain control, divert and safely land the aircraft.
Investigators learned that although the PCM had been routinely inspected, there was no inspection guidance or requirement for the manifold housing. Repeated motions of the PCM caused the fatigue cracks that eventually gave way on a part that was expected to outlive the aircraft itself. In other words, the designer and manufacturer made assumptions that proved erroneous.
The lesson for aviation professionals? It is one thing to learn from the mistakes of the past, but our challenge is to use those experiences to help predict the future. Designers and engineers must not give in to assumptions, but rather try to predict the unpredictable.
Another subset of mechanical failures is design issues that have resulted in loss of life. A season 5 episode revolved around multiple DC-10s that experienced explosive decompression, caused by a door design meant to allow more cargo to be loaded. Instead, a crash occurred when the latches failed on the outward opening cargo door. The first failure led to a redesign, yet the problem happened again and brought down a second aircraft. In season 4, we are shown three Boeing 737-200 aircraft that over a five-year period in the 1990s suffered full deflection of their rudders without input from the pilots. This caused at least 150 deaths due to a design flaw with the rudder control system before one flight crew managed a successful landing, preserving the evidence that revealed the cause.
Maintenance mistakes
Another common cause seen in the show is poor maintenance or botched practices. In season 11, technicians overlooked reinstalling the screws that held the leading edge in place on a horizontal stabilizer. Signoffs were incomplete and inspections were missed. The leading edge separated from the aircraft while on approach to land, rendering it completely unflyable.
In season 2, a pilot was partially sucked out a cockpit window because a maintenance worker installed incorrectly sized bolts holding the cockpit window in place. And in season 23, a flight crew battled with an airliner where the aileron cables had been installed backward. Each of these maintenance errors was the last link in an error chain that started with the design, documentation, instructions and execution of the repair.
The lesson is that aviation professionals should not rely on someone else breaking the error chain, but must remain diligent at every step of the process.
Flight crew error
Mistakes by the flight crew or pilots appear to be the most common cause, as determined by the investigator reenactors. Several episodes deal with the flight crew’s misinterpretation of cockpit instruments or displays (season 6, episode 3) or distractions when interfacing with the aircraft’s systems or autopilot (season 9, episode 7).
There could be any number of lessons here: How can designers and aerospace engineers plan for errors that pilots make? Can there be better displays and machine-human interfaces so pilots are better aware of unusual situations and how to appropriately respond? With commercial piloting offering hours and months of consistently expected operations punctuated by moments of unanticipated events, can there be better training through advanced simulation to keep pilots prepared for the unexpected? Or does adding additional automation to assist an overwhelmed flight crew or taking the human out of the flight deck become the answer?
For another opinion, I turned to Robert Sumwalt, former chairman of the National Transportation Safety Board and executive director of the Boeing Center for Aviation and Aerospace Study at Embry-Riddle Aeronautical University. “People sometimes ask me what percentage of accidents are attributed to human error,” he said. “I reply that nearly 100% of accidents I’ve studied — and there are literally hundreds — have human error somewhere in the system.”
“It may be an error of a front-line operator, such as a pilot, technician, or air traffic controller, but if we dig far enough, we may find those errors have roots tracing back further in the system, such as a design or engineering issue that wasn’t detected until the crash investigation,” he continued. “There is great learning value from learning from the mistakes of others, and that learning can transpire by watching a well-produced documentary.”
The aerospace industry is poised to enter a period where new aircraft will be designed and new space transportation systems will be developed. Passenger safety will depend on quality design, development, manufacturing, maintenance and operation. The tools used and attitudes employed will determine if we have learned from the past to expect the unexpected.
