NTSB Identification: LAX99LA181.
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Accident occurred Thursday, April 15, 1999 in LA VERNE, CA
Probable Cause Approval Date: 11/22/2000
Aircraft: Piper PA-31-310, registration: N57AS
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The aircraft had been in maintenance for an adjustment to the right engine manifold pressure differential controller. The procedure required the uncowling of the engine. A certificated airframe and powerplant mechanic removed the cowling and made the required adjustments, then left for the day. A noncertificated mechanic replaced the cowling and the pilot then proceeded to perform the postmaintenance test flight. During climbout, the right engine upper cowling separated and wrapped around the right horizontal stabilizer. The pilot experienced difficulty in controlling the aircraft until the airspeed was reduced, then he returned to the airport and landed. Inspection of the cowling disclosed that the inboard latches on the upper cowling were not damaged. In his written statement, the pilot notes that his failure to detect the unlatched inboard cowling fasteners resulted from 'poor preflight inspection habits and a failure to follow the checklist.'

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The in-flight separation of the right engine cowling due to the operator's inadequate maintenance quality control procedures and the pilot's inadequate preflight inspection.

Full narrative available

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