Narrative:

A test flight was being conducted following maintenance on the right engine. Due to time constraints, a hasty preflight was conducted. After takeoff and climb, the aircraft was leveled at 3500 ft, power reduced and cowl flaps closed. Soon thereafter, the right engine cowling (upper) separated, striking the horizontal stabilizer. The aircraft responded with a rapid nose down pitch change followed by a nose up. The sequence repeated through several cycles intensifying with each cycle. A mayday call was made. Power was then reduced and as the airspeed slowed, aircraft control was regained albeit somewhat difficult. The engine cowling was observed to be wrapped around the right horizontal stabilizer. The aircraft was then returned to brackett and a flapless landing made without further incident. Clearly the cause of the incident was an inadequate preflight inspection as the separation of the cowling occurred due to the inbound fasteners not being locked. These items are included on the preflight inspection checklist. Contributing to the incident was the failure of the maintenance personnel to secure the fasteners. Callback conversation with reporter revealed the following information: the reporter stated the cowling fasteners are flat head screw type fasteners and they appear the same locked or unlocked. The reporter said the cowling fasteners were the subject of an airworthiness directive to add witness marks to indicate the cowling fastener status, locked or unlocked. The reporter said the preflight inspection was done in haste and the fasteners were overlooked. The reporter stated the FAA is investigating the incident.

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Original NASA ASRS Text

Title: A PIPER PA31-310 IN CRUISE AT 3500 FT DECLARED AN EMER AND DIVERTED DUE TO THE R ENG COWLING SEPARATING AND WRAPPING AROUND THE R HORIZ STABILIZER. INCIDENT CAUSED BY UNSECURED INBOARD FASTENERS.

Narrative: A TEST FLT WAS BEING CONDUCTED FOLLOWING MAINT ON THE R ENG. DUE TO TIME CONSTRAINTS, A HASTY PREFLT WAS CONDUCTED. AFTER TKOF AND CLB, THE ACFT WAS LEVELED AT 3500 FT, PWR REDUCED AND COWL FLAPS CLOSED. SOON THEREAFTER, THE R ENG COWLING (UPPER) SEPARATED, STRIKING THE HORIZ STABILIZER. THE ACFT RESPONDED WITH A RAPID NOSE DOWN PITCH CHANGE FOLLOWED BY A NOSE UP. THE SEQUENCE REPEATED THROUGH SEVERAL CYCLES INTENSIFYING WITH EACH CYCLE. A MAYDAY CALL WAS MADE. PWR WAS THEN REDUCED AND AS THE AIRSPD SLOWED, ACFT CTL WAS REGAINED ALBEIT SOMEWHAT DIFFICULT. THE ENG COWLING WAS OBSERVED TO BE WRAPPED AROUND THE R HORIZ STABILIZER. THE ACFT WAS THEN RETURNED TO BRACKETT AND A FLAPLESS LNDG MADE WITHOUT FURTHER INCIDENT. CLRLY THE CAUSE OF THE INCIDENT WAS AN INADEQUATE PREFLT INSPECTION AS THE SEPARATION OF THE COWLING OCCURRED DUE TO THE INBOUND FASTENERS NOT BEING LOCKED. THESE ITEMS ARE INCLUDED ON THE PREFLT INSPECTION CHKLIST. CONTRIBUTING TO THE INCIDENT WAS THE FAILURE OF THE MAINT PERSONNEL TO SECURE THE FASTENERS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE COWLING FASTENERS ARE FLAT HEAD SCREW TYPE FASTENERS AND THEY APPEAR THE SAME LOCKED OR UNLOCKED. THE RPTR SAID THE COWLING FASTENERS WERE THE SUBJECT OF AN AIRWORTHINESS DIRECTIVE TO ADD WITNESS MARKS TO INDICATE THE COWLING FASTENER STATUS, LOCKED OR UNLOCKED. THE RPTR SAID THE PREFLT INSPECTION WAS DONE IN HASTE AND THE FASTENERS WERE OVERLOOKED. THE RPTR STATED THE FAA IS INVESTIGATING THE INCIDENT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.