Piper PA28R N963WW accident near Peoria, Arizona

Probable cause

A loss of engine power for reasons that could not be determined because postaccident examination did not reveal any anomalies that would have precluded normal operation.

NTSB analysis

At 8,500 feet, the designated pilot examiner instructed the commercial pilot to demonstrate steep spirals. The pilot configured the airplane by placing the mixture control to the FULL RICH position, entered the spiral maneuver, and cleared the engine every 180 degrees while in the turn. After the fourth spiral, the pilot attempted to make a simulated emergency landing, but when he observed that he was high, he put the airplane into a slip to lose altitude. When the examiner instructed the pilot to go around, the pilot advanced the throttle, but the engine did not respond. The pilot subsequently landed the airplane long, and it ran off the end of the runway.

During the postaccident examination, the engine was run with no anomalies noted. The inspector subsequently discussed with the flight school’s chief flight instructor the procedure for setting the mixture control to the FULL RICH position at altitude before initiating a maneuver such as steep spirals. The chief instructor alluded to information provided by the engine manufacturer that the recommended procedure is to set the mixture to FULL RICH below 5,000 feet. After the accident, the chief instructor issued a company policy statement which read, “When leaned at altitude for flight, students and instructors should gradually enrichen the mixture throughout the descent, reaching full rich mixture while descending through 4,000 feet.” According to Service Instruction No. 1094D, issued by the engine manufacturer on March 25, 1994, relative to fuel mixture leaning procedures for all of the manufacturer's Opposed Series Engines, “For 5,000 feet density altitude and above or high ambient temperatures, roughness or reduction of power may occur at full rich mixture.”

A representative for the engine manufacturer stated that the mixture setting during a low-power descent is not really a concern and that the mixture only needs to be adjusted when the engine power is required during takeoff, climb, and cruise. The engine representative added that if the pilot had put the mixture to full rich and descended, the engine would have been fine and should not quit. Therefore, while it may have been possible that the placement of the mixture to the FULL RICH position at altitude could have resulted in the power interruption at the lower altitude, there is no definitive evidence to support this position. The reason for the reported loss of engine power could not be determined.

Text from the NTSB. Open the NTSB docket for WPR12LA247 for the full record.