PIPER PA 22 near Skwentna, AK — 2015-06-01

Probable cause

The pilot's failure to follow the airplane's operating limitations by rapidly opening the throttle, which resulted in a loss of engine power. Contributing to the accident was the pilot's decision to maneuver the airplane at low altitude even though he was not taking off or landing.

NTSB narrative

The pilot stated that he was maneuvering the airplane at low altitude to practice approaches at an unimproved airstrip. After passing over some trees in a northerly direction, the airplane began a rapid descent. The pilot applied full power in an effort to correct for the descent, but the engine power decreased. When the airplane was about 25 ft above ground level, the left wing struck a tree, and the airplane then impacted terrain in a slight left bank. The airplane slid along the ground for about 18 ft before impacting a berm, which caused the airplane to become airborne and rotate counterclockwise 180 degrees before coming to rest in a near-level pitch attitude. A Federal Aviation Administration airworthiness directive (AD) applicable to the airplane required that a placard with the following operating limitation be placed near the throttle: "DO NOT OPEN THROTTLE RAPIDLY – (IDLE TO FULL THROTTLE, 2 SECONDS MINIMUM.)" The AD was issued to prevent power interruption and acceleration hangup that could result from abrupt throttle movement. The airplane was in compliance with the AD. The pilot stated that, when he opened the throttle, he did so rapidly, faster than the 2-second requirement. It is likely that the pilot's rapid opening of the throttle interrupted the fuel supply to the engine, which resulted in a loss of engine power.

Analysis

Primary failure mode

Engine power loss

First missed decision gate

Pilot could have advanced throttle more slowly to prevent power loss.

NTSB coding

• Loss of engine power (total) · Maneuvering-low-alt flying
• Decision Making / Judgment

Evidence available

• 3 docket documents

Docket documents3

• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Memorandum for Record - Telephone Interview, Pilotinterview
• FAA Airworthiness Directive 73-09-06other

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