The Boeing 737 is the most popular passenger plane in the world. Over 6,000 have been made since they came into service in the late sixties.They have one of the best safety records and have flown millions of hours. In the eighties one suddenly rolled on its back when it was about to land and crashed killing everyone on board. A few years later another did the same thing over Baltimore. It crashed with no survivors. The National Transportation Safety Board had spent two years investigating the crash but had not found a definitive reason. 

Then it happened again and they realised there was a link and suspected the rudder motor servo malfunctioning but couldn’t prove it. When it happened for a third time in 1996 the plane survived and made a normal landing but now they had a crew who had survived.Because Eastwind Flight 517 had landed safely, the NTSB was also able to perform tests on a plane that had experienced problems similar to the accident aircraft.

In addition, because the pilots of Flight 517 had survived, the NTSB was able to interview them and gain additional information on their experience. The flight’s captain told the NTSB in a post-accident interview that they had not encountered any turbulence during the flight, and that, during their landing descent, he felt the rudder “kick” or “bump” even though neither pilot had moved the rudder pedals. 

When the plane abruptly rolled to the right, the captain applied left aileron and attempted to move the rudder, but the rudder pedal controls felt stiffer than normal and did not seem to respond to his input. When his flight control inputs did not immediately resolve the roll upset, he also advanced the throttle of the right engine in an effort to compensate.

On March 24, 1999, after a four-year investigation, the NTSB issued its probable cause finding for Flight 427. The NTSB concluded that the probable cause of the Flight 427 crash was rudder reversal due to the PCU servo malfunction.Two years later, the NTSB published an amended accident report for Flight 585 that found the same probable cause for that accident as well.

As a result of the NTSB’s findings, the Federal Aviation Administration ordered that the servo valves be replaced on all 737s by November 12, 2002. The FAA also ordered new training protocols for pilots to handle in an unexpected movement of flight controls.

I recently made a documentary for Discovery Channel about the story of this fascinating mystery.

We shot dramatic recreations of all three flights, the crashes and the investigation. This gave me the opportunity to interview the actual investigators and the surviving pilot in the US, visit the site of the Baltimore crash, interview relatives of people who had died in the crashes including the pilot, the members of the NTSB team and aviation experts. 

It was the most complicated edit I have worked on and keeping three separate stories spinning in chunks throughout was challenging.

You can watch it here.