A preliminary report released by the Nepalese Aircraft Accident Investigation Commission attributes a deadly crash to pilot error. When the ATR-72 aircraft crashed into a gorge in Nepal’s mountainous Pokhara region on Jan. 15, all of the 72 passengers and crew on board lost their lives. Investigators reached their conclusions after comparing information collected from the aircraft’s data recorder with a cockpit audio recording. They discovered that what the pilots said they were doing did not match their actual inputs in the seconds before the plane lost altitude and crashed.
Propellers feathered instead of flaps deployed
Both of the pilots in the cockpit were captains, which means they were highly skilled and experienced aviators. The pilot flying at the time of the aviation accident was familiarizing himself with the airport approach. The pilot monitoring him was an instructor. The pilot flying clearly states in the cockpit recording that he was deploying the plane’s flaps to prepare for landing. What he actually appears to have done is pull a lever that feathered the aircraft’s propellers. Propellers use less fuel when they are feathered, but they produce no thrust.
No time to recover
The layout of the ATR-72 cockpit suggests that the pilot flying simply pulled the wrong lever as the levers to feather the aircraft’s propellers and deploy its flaps are adjacent to one another. When this happened, both engines reduced power by about 25%. An audio alert warned the pilots about the drop in power about 10 seconds after the propellers were feathered, and a stick shaker device activated twice to warn them about a possible stall. However, by the time the pilots realized their mistake, the aircraft was already very low, and they did not have enough time or altitude to recover.
Two captains, and still a mistake
It is difficult to believe that two experienced captains could make such a simple error, but the electronic and audio evidence appears to be compelling. This kind of mistake rarely leads to an accident when planes are traveling at high altitudes, but there is no room for error when an aircraft makes a final approach.