The Weekly Reflektion Week 21 / 2020

This week’s Reflektion concerns an aircraft incident in 1972 which, if lessons had been properly identified and mitigating actions implemented, would have prevented the deaths of 346 people less than two years later in an air crash outside Paris.

Learning lessons from our own incidents, and from other incidents is an important part of our job. How effective are we at learning lessons, and implementing them successfully? Even small incidents potentially have important learnings that can be uncovered in investigations. Does your company have an effective learning process, and the stamina and determination to implement changes?

On June 12th, 1972, American Airlines flight 96 from Detroit to La Guardia, New York had just taken off and was climbing to cruising height. The McDonnell Douglas DC-10 was a relatively new plane, introduced 2 years earlier, and this one was number 5 off the production line. Five minutes after take-off, the aft cargo door burst open causing an explosive decompression, which, in turn, caused a collapse of the cabin floor immediately over the cargo door. This severed the hydraulics that controlled the aircraft rudder, and ailerons, the surfaces that make the aircraft turn and bank, leaving the pilots with little control of the plane.

The pilot was very experienced and had trained the previous year on a simulator in preparation for the introduction of the DC-10. One concern he had was that there was no back-up system to the hydraulics in the DC-10 in case of failure.  There was a back-up system in the older aircraft designs the pilot had previously flown. He spent hours repeatedly testing his alarming hypothesis of total hydraulic system failure and learned how to exploit the DC-10’s exceptional ability to fly on its engines without assistance from the rudder or ailerons.

Using only the engines he managed to turn the plane around and set the plane up to land back at Detroit. To maintain control of the plane with only the engines, the plane had to approach the runway faster than normal, and full reverse thrust was applied to the engines as soon as the plane touched down. The plane veered off the runway to the right. The pilot then applied full throttle to the right engine, bringing the plane back to the runway, stopping successfully within the airport perimeter. The 56 passengers and 11 crew were unhurt.

To maximize the working space within the cargo-hold of the DC-10, the cargo doors opened outwards, leading to the possibility of them being forced open at altitude under normal in-flight pressure. To prevent this, a special latching system was used that locked shut under pressure when properly closed. To ensure the latches were properly positioned, a handle on the outside of the door pressed small metal pins into the latches, and if the latches were in the improper location the pins would not align and the handle would not close. The investigation concluded that due to poor design it was possible to close the handle on doors despite the latches being in the wrong position. A design change was issued, but McDonnel Douglas made it voluntary rather than compulsory. It was also found that the cabin floor lacked pressure relief vents to that would allow pressure equalization in such an event, thus preventing floor collapse.

Less than 2 years later, on March 3rd, 1974, Turkish Airline flight 981 from Istanbul to London with an intermediate stop in Paris, also suffered an explosive decompression when the same cargo doors failed taking off from Paris. All the 346 on board were killed. The investigation found that the hydraulic control lines had been cut by the collapse of the cabin floor, and 77 seconds after the cargo door failure, the aircraft crashed in a forest outside Paris. It was found that the cargo door design modification had not been made, but a notice in both English and Turkish had been introduced as a mitigating action, warning the cargo handlers of the issue. In Paris, the cargo handler could understand neither English nor Turkish.

It was also found that a similar set of conditions, which had caused the failure of an aircraft floor following explosive decompression of the cargo hold, had occurred in ground testing in 1970 before the DC-10 series entered commercial service. 

When you identify actions to avoid repetition of incidents, or to improve performance, how do you follow these up to ensure continuous improvement? Is your organisation good at identifying learning points and implementing them? Do you actively seek out incidents and accidents that may be related to your operation and try to learn from them?

Reflekt AS