THE HUMAN ERROR
mountain on the other side of the river. His left foot quickly pushed the rudder to the floor, but as he cranked in left aileron the trees seemed to be right in front of him. In his exact words he told me: “I didn’t know what was going on, but I knew that we were going to die if this kept up.” He pulled both throttles to idle and dropped the aircraft into the waiting river just under them. One logger failed to exit the sinking aircraft in time and drowned. The turbocharger controller is fail- safed to open via a spring to dump all the exhaust overboard via the wastegate, so as not to over boost the engine in the event of the failure of the oil control supply to counteract it. The oil supply counteracts the spring through an orifice and a controller.
One or more pieces of Teflon tape managed to suddenly block the orifice, causing the wastegate to go to full fail-safe open. This dropped the manifold pressure to 28 inches resulting in a significant loss of power. However the Teflon squeezed through and the controller now dumped full oil pressure from the controller to the waste-gate actuator resulting in a brief over-boost as the controller moved to restore normal boost. In that brief over-boost time period, the pilot, now in an emotional near panic condition, made the subconscious (Child) decision to chop all power and drop the aircraft into the water. If he had had more time to make a rational decision, all he had to do was pull the power back on the left engine only until he could readjust the trim. Unfortunately, one person would pay the ultimate price for this human error.
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Was this the first time this had happened? Unfortunately, not. During my years with a major airline I recall an incident that cost the company over $250,000 1970s dollars. The culprit again was the arch villain of aviation, Teflon tape. I worked on the ramp at that time and refueled one of our 747s to full capacity of 50,000 gallons for a flight to Hong Kong. After doing the pushback we had a bit of spare time before the next flight when all of a sudden, a crew member came running in to say that the aircraft was coming back. We went back out to see it do a fly- past with all the gear down. It had just finished dumping thousands of gallons of fuel somewhere and after the fly-past it made a circuit and landed with every fire truck at the airport chasing it down the runway. We guided it back into the gate and were told that one of the main gear had failed to retract after take off. The passengers were off loaded, and the aircraft was towed to the hangar. There, they placed it on jacks and did a series of successful retraction tests. All hydraulic filters were changed and the aircraft was returned to the gate for refueling and loading of what were likely some now nervous passengers. While I wasn’t there, I suspect that everyone was watching this takeoff where, once again Murphy’s law prevailed and one of the main gear again failed to retract. Once more, the city of Vancouver would be treated to a JP4 bath and the usual fanfare of fire trucks would be part of the arrival reception party. The aircraft was once more towed to the hangar with the orders to do whatever you have to do, but this must NOT happen again. While the 300 plus passengers slept compliments of the airline, every component in the landing gear system was replaced in time for a morning departure. A lot less passengers boarded the aircraft with the hope of 3rd time lucky.
Our crew did not depart the
aircraft, but we and likely everyone at the airport watched as it climbed out and all the gear retracted as normal. So the problem had to be in the pile of components on the component overhaul shop floor. Under the watch eye of the quality control inspectors, each component was disassembled. One of the main gear door sequence valves finally revealed the source of the problem. As you would have guessed by now, it was a small piece of Teflon tape that was floating around in it. They say that they went through every tool box in the hangar looking for that roll of tape. Thank goodness I had taken it home – just kidding. Teflon tape can be a silent killer. It can wait a long time and strike when you least expect it. Don’t use it on any aircraft component or it could be you who contributes to what can be a costly human error.
Gordon Dupont worked as a special programs coordinator for Transport Canada from March 1993 to August 1999. Prior to working for Transport,
Dupont worked for seven years as a technical investigator for the Canadian Aviation Safety Board (later to become the Canadian Transportation Safety Board). He saw firsthand the tragic results of maintenance and human error. Dupont has been an aircraft maintenance engineer and commercial pilot in Canada, the United States and Australia. He is the past president and founding member of the Pacific Aircraft Maintenance Engineers Association. He is a founding member and a board member of the Maintenance and Ramp Safety Society (MARSS). Dupont, who is often called “The Father of the Dirty Dozen,” has provided human factors training around the world. He retired from Transport Canada in 1999 and is now a private consultant. Visit
www.system-safety.com for more information.
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