1995-07-17: Air Tractor AT-301 (N4326S) — Roberts, ID
On July 17, 1995, an Air Tractor AT-301 (registration N4326S) was involved in an aviation accident near Roberts, ID. Investigators recorded the probable cause as: A LOSS OF ENGINE POWER DUE TO THE SEPARATION OF THE NUMBER 3 CYLINDER EXHAUST VALVE ROCKER ARM SHAFT FROM THE CYLINDER HEAD, WHICH DISABLED MOVEMENT OF THE EXHAUST VALVE. A FACTOR WAS THE LACK OF SUITABLE TERRAIN FOR THE FORCED LANDING. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
Probable cause
A LOSS OF ENGINE POWER DUE TO THE SEPARATION OF THE NUMBER 3 CYLINDER EXHAUST VALVE ROCKER ARM SHAFT FROM THE CYLINDER HEAD, WHICH DISABLED MOVEMENT OF THE EXHAUST VALVE. A FACTOR WAS THE LACK OF SUITABLE TERRAIN FOR THE FORCED LANDING.
— NTSB Determination
Accident narrative
THE PILOT REPORTED THAT SHORTLY AFTER TAKEOFF, AT 40 FEET ABOVE GROUND LEVEL, THE ENGINE LOST POWER AND BEGAN BACKFIRING. THE PILOT MADE A FORCED LANDING IN A BARLEY FIELD WITH 3-FOOT-TALL CROPS, AND THE AIRPLANE CARTWHEELED. POSTACCIDENT EXAMINATION OF THE ENGINE REVEALED THAT THE EXHAUST VALVE ROCKER ARM HOUSING ON THE NUMBER 3 CYLINDER SEPARATED, DISABLING THE NUMBER 3 CYLINDER EXHAUST VALVE.