(August 2011) It has often been said that accidents result not from one big cause, but from a lot of little ones that happen to converge in some unforeseen way. Nevertheless, many fatal accidents do arise from one simple cause: VFR pilots flying into IFR weather. This happens so regularly, and in so monotonous a pattern, that I seldom write about it, since there seems to be so little to say about any given instance. I prefer, if one can be said to prefer one type of sad event to another, to examine accidents whose causes are more complex and thought provoking.
Another truism is that mechanical failures are comparatively rare; most accidents are precipitated by some pilot action or omission. Such mechanical failures as do occur fall into various categories — materials failures, maintenance errors and so on. Of these categories, one of the least populous, but of the greatest practical interest, is that of accidents that are due to engineering. These accidents arise from unexpected interactions of seemingly benign or unrelated design features. This is the soil in which certification requirements, and liability lawsuits, sprout and proliferate.
In January 2009, a two-pilot Sikorsky S-76C of PHI (formerly Petroleum Helicopters Inc.) carrying seven passengers in VFR conditions from an onshore heliport in Louisiana to a Gulf of Mexico oil platform crashed a few minutes after takeoff. One passenger survived with serious injuries — “a miracle,” his attorney said.
The helicopter was equipped with a combined flight data and cockpit voice recorder. A few seconds before the end of the recording, there was a loud bang, followed by a sound of rushing wind and a loss of rotor rpm. “What the hell happened?” exclaimed the second pilot. “Low rotor,” the first pilot said, and the other replied, “I can’t hear you!” The recording ended a few seconds later.
Investigators identified remains of a female red-tail hawk on the helicopter’s shattered windshield and other parts of the airframe, and concluded that what caused the accident was a bird strike when the helicopter was 850 feet above the ground and moving at about 135 knots. The bird had hit the aluminum brow of the cabin just above the windshield, fracturing the acrylic but not entering the cabin.
The throttle quadrant is located in the ceiling, along the centerline and slightly behind the windscreen. It contains two power levers (called ECLs, for engine control levers) and, between them and the windshield, two fire extinguisher T-handles. The T-handles are about four inches behind the edge of the windshield and are normally held in a forward position by a spring-loaded detent. If a fire extinguisher handle is pulled aft, it automatically releases the associated ECL, allowing it to move backward and reduce fuel flow to that engine. If the T-handle is pulled all the way aft, it also shuts off fuel to the affected engine.