Two pieces cut from the top of plastic shipping caps kicked around the fuel lines of a U.S. Army Armed Reconnaissance Helicopter (ARH) prototype for a week before they fell in place to starve its engine of fuel and lead to the aircraft’s destruction Feb 21.
The pieces were cut loose when a Bell Helicopter worker screwed check valves onto the aircraft’s fuel boost pump, according to an investigation by the U.S. National Transportation Safety Board and those familiar with it. The caps, which covered the pump’s check-valve ports, should have been removed. Most ARH boost pumps are assembled by the pump manufacturer. But Bell built up this one at its Army Programs Center at Fort Worth Alliance Airport, Texas about a month before the crash. The Honeywell HTS900-1 engine went through ground runs the week before the Feb. 21 maiden flight.
On that flight, the two pilots — one each from Bell and the Army — performed "quick stop" maneuvers from high speed to hovers in and out of ground effect. About 20 min into the flight, as the Bell test pilot, who had 3,150 hr, started a test flight sequence that called for configuration for slow flight in a shallow descent, the engine flamed out. The pilot smoothly executed an autorotation with a 180-deg left turn to the fairway of a golf course. But the skids dug into the fairway’s soft ground, causing the aircraft to tip and roll. It was totaled in the subsequent wreck.
An official finding of probable cause must await a formal review and vote by the NTSB’s members.