Narrative:

On this date I had flown a PA32 on a part 135 cargo flight from ZZZ1 to ZZZ. While en route the cowling on the aircraft had blown off in multiple pieces while in level cruise; 5500 ft; and an indicated airspace of 140 KIAS. This location is within a few mi west of the X mountains. I was currently in contact with ZZZ approach control with an assignment to fly direct to X lake and expect a hold of 15 mins during the time of incident. First thing that came to mind was to fly the airplane. I elected to let the plane fly a couple of mi before making any adjustments; therefore; troubleshooting the aircraft was my first plan of action. After deciding that the aircraft was flying normally minus the cowling; I decided to reduce the manifold pressure so the aircraft would fly level at an indicated airspeed of 100 KIAS; an airspeed within the white arc. At this point I'm a few mi east of the mountains and have come to the conclusion that the airplane is ok to fly to the most suitable airport. Now my decision is where to land the aircraft? My choices were ZZZ; ZZZ2 or ZZZ3. I told myself upon reaching X lake this would be my decision point of where to land; since this is a fairly central mark to the 3 locations I found it as an appropriate location to make my final decision. At this point I made the decision to land and not to declare an emergency. I didn't feel that calling an emergency was a priority to get in any faster; since my concern was to fly the aircraft smooth and safely while in a normal traffic pattern. After landing at ZZZ; I made the calls to my director of operations and chief pilot to explain this incident. Contributing factors consist of fatigued fabric glass cowlings and the possible front in post not attached to the front side of the cowling. The next day other cowlings of PA32's were inspected and 1 cowling was not attached to the post on the front inner side of the cowling. I believed this was the main contributing factor to this particular incident. Callback conversation with reporter revealed the following information: the reporter stated the exact cause is unknown but it is suspected the cowling alignment posts located in the forward past of the engine cowling and left side of the propeller drive were misaligned or broken. The cowling right and left side latches were latched on the preflight check but the alignment posts cannot be seen. The aircraft incurred no damage other than the departed cowling.

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Original NASA ASRS Text

Title: A PA32 IN CRUISE AT FL550 HAD THE ENG COWLING DEPART THE ACFT IN 2 SEPARATE PIECES.

Narrative: ON THIS DATE I HAD FLOWN A PA32 ON A PART 135 CARGO FLT FROM ZZZ1 TO ZZZ. WHILE ENRTE THE COWLING ON THE ACFT HAD BLOWN OFF IN MULTIPLE PIECES WHILE IN LEVEL CRUISE; 5500 FT; AND AN INDICATED AIRSPACE OF 140 KIAS. THIS LOCATION IS WITHIN A FEW MI W OF THE X MOUNTAINS. I WAS CURRENTLY IN CONTACT WITH ZZZ APCH CTL WITH AN ASSIGNMENT TO FLY DIRECT TO X LAKE AND EXPECT A HOLD OF 15 MINS DURING THE TIME OF INCIDENT. FIRST THING THAT CAME TO MIND WAS TO FLY THE AIRPLANE. I ELECTED TO LET THE PLANE FLY A COUPLE OF MI BEFORE MAKING ANY ADJUSTMENTS; THEREFORE; TROUBLESHOOTING THE ACFT WAS MY FIRST PLAN OF ACTION. AFTER DECIDING THAT THE ACFT WAS FLYING NORMALLY MINUS THE COWLING; I DECIDED TO REDUCE THE MANIFOLD PRESSURE SO THE ACFT WOULD FLY LEVEL AT AN INDICATED AIRSPD OF 100 KIAS; AN AIRSPD WITHIN THE WHITE ARC. AT THIS POINT I'M A FEW MI E OF THE MOUNTAINS AND HAVE COME TO THE CONCLUSION THAT THE AIRPLANE IS OK TO FLY TO THE MOST SUITABLE ARPT. NOW MY DECISION IS WHERE TO LAND THE ACFT? MY CHOICES WERE ZZZ; ZZZ2 OR ZZZ3. I TOLD MYSELF UPON REACHING X LAKE THIS WOULD BE MY DECISION POINT OF WHERE TO LAND; SINCE THIS IS A FAIRLY CENTRAL MARK TO THE 3 LOCATIONS I FOUND IT AS AN APPROPRIATE LOCATION TO MAKE MY FINAL DECISION. AT THIS POINT I MADE THE DECISION TO LAND AND NOT TO DECLARE AN EMER. I DIDN'T FEEL THAT CALLING AN EMER WAS A PRIORITY TO GET IN ANY FASTER; SINCE MY CONCERN WAS TO FLY THE ACFT SMOOTH AND SAFELY WHILE IN A NORMAL TFC PATTERN. AFTER LNDG AT ZZZ; I MADE THE CALLS TO MY DIRECTOR OF OPS AND CHIEF PLT TO EXPLAIN THIS INCIDENT. CONTRIBUTING FACTORS CONSIST OF FATIGUED FABRIC GLASS COWLINGS AND THE POSSIBLE FRONT IN POST NOT ATTACHED TO THE FRONT SIDE OF THE COWLING. THE NEXT DAY OTHER COWLINGS OF PA32'S WERE INSPECTED AND 1 COWLING WAS NOT ATTACHED TO THE POST ON THE FRONT INNER SIDE OF THE COWLING. I BELIEVED THIS WAS THE MAIN CONTRIBUTING FACTOR TO THIS PARTICULAR INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE EXACT CAUSE IS UNKNOWN BUT IT IS SUSPECTED THE COWLING ALIGNMENT POSTS LOCATED IN THE FORWARD PAST OF THE ENG COWLING AND L SIDE OF THE PROP DRIVE WERE MISALIGNED OR BROKEN. THE COWLING R AND L SIDE LATCHES WERE LATCHED ON THE PREFLT CHK BUT THE ALIGNMENT POSTS CANNOT BE SEEN. THE ACFT INCURRED NO DAMAGE OTHER THAN THE DEPARTED COWLING.

Data retrieved from NASA's ASRS site as of January 2009 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.