Narrative:

On the night of dec/xa/08; aircraft was in ZZZ for maintenance. Myself and another amt were working to close the #1 engine by lowering; latching and inspecting the closing of the fan; reverser; and core cowls. On the first flight of the day; aircraft X took off from ZZZ and lost the #1 engine core cowls which resulted in exterior damage to the #1 engine left wing flaps just behind #1 engine and left horizontal stabilizer. To the best of my recollection; the core cowls were latched closed. There are 3 lower latches that lock down the core cowl. I was told that of the three; the forward and mid latches were intact and the aft was ripped apart; to suggest that maybe the forward and mid latches were not secured. The amt I was working with said that he remembers them being up and latched. If they were not latched they would be hanging down. I cannot say for certain if the forward and mid latches were secured; only that they appeared to be. After we released the airplane for service; tug moved aircraft X to a gate. If the latches were not properly secured; they should have perhaps fallen in the move but maybe they were jammed in the up position and did not fall. That's the only thing I can speculate as to what may have happened. Supplemental information from acn 816911: aircraft was due #1 engine mount isolator inspection. #1 engine fan cowls; reverser cowls; and core cowls were opened for the inspection. The inspection boroscope team performed the inspection of the engine mounts. When the boroscope inspection team had completed the inspection; mr. X and I closed the engine. Before we closed the fan cowls; mr. X and I ensured all the latches were latched and secured on the reverser cowls. Then mr. X and I closed the fan cowls and core cowls; ensuring all latches were latched and secured. Supplemental information from acn 816916: after a normal preflight and taxi out; we were cleared for takeoff. I was the pilot flying. Shortly after liftoff; another aircraft reported to the tower that our left engine lost what appeared to be a part of our unpainted engine cowling as we were on our takeoff roll. We switched to departure and I had the first officer request from ATC a leveloff at 5000 ft MSL and radar vectors. I called for the gear and flaps to up; kept the aircraft at clean maneuvering speed; engaged the autopilot; called for the after takeoff checklist; then transferred control of the aircraft and radios to the first officer. There had been no abnormal handling issues or abnormal engine indications during the takeoff roll or after liftoff. I called the cabin and told the head flight attendant what had been reported to us and asked him to walk back and take a look at the left engine cowling area. He reported back to me that the unpainted portion of the engine cowling on the tail cone section of the left engine was damaged and mostly gone. I told him we would be returning; making a normal approach and lndg and would be on the ground in approximately 10 minutes; and that I would make a public announcement to the passengers after I spoke with maintenance and dispatch. After consulting with maintenance and flight control; the decision to return was agreed upon by all 3 parties. I did not see a need to declare an emergency; since there were no abnormal handling issues or abnormal engine indications. I made a public announcement to the passengers that we were making a precautionary return due to the loss of some engine cowling and assured them that the engine and aircraft were operating normally. We made a normal approach and landing and taxied the aircraft uneventfully to the gate. Upon initial inspection at the gate by maintenance; they were able to confirm that the unpainted portion of the cowling on the tail cone section had indeed departed the aircraft. It appeared that there was a hole in part of the honeycombed section aft of the cowling on the bottom side of the tail cone and possibly some minor damage to the trailing edge flap directly aft of the left engine. Maintenance was unable to determine yet at that point if the fastener latches had failed or had not been properly latched and secured (several pieces of the cowling had been retrieved by airport operations). The first officer; who had conducted the preflight inspection; was adamant that the latches had at least appeared to be fastened and secured during his walkaround. Supplemental information from acn 817570: I was the first officer and initially pilot monitoring the flight. Preflight including briefings and the aircraft walkaround was completed and no abnormalities were detected. The aircraft was boarded and dispatched routinely. Callback conversation with reporter acn 816910 revealed the following information: reporter stated the inboard and outboard core cowls on #1 engine basically ripped away from the lower aft latch; shortly after takeoff. There are three latches that are used to secure the core cowl. Part of the cowling was still attached to the cowl upper hinge line on the engine pylon of the B757-200.

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Original NASA ASRS Text

Title: A Mechanic; Lead Mechanic; Captain and First Officer report on the separation of the #1 engine core cowls on a B757-200 shortly after takeoff; with damage to the left wing flaps and horizontal stabilizer.

Narrative: On the night of Dec/XA/08; aircraft was in ZZZ for maintenance. Myself and another AMT were working to close the #1 engine by lowering; latching and inspecting the closing of the fan; reverser; and core cowls. On the first flight of the day; Aircraft X took off from ZZZ and lost the #1 engine core cowls which resulted in exterior damage to the #1 engine left wing flaps just behind #1 engine and left horizontal stabilizer. To the best of my recollection; the core cowls were latched closed. There are 3 lower latches that lock down the core cowl. I was told that of the three; the forward and mid latches were intact and the aft was ripped apart; to suggest that maybe the forward and mid latches were not secured. The AMT I was working with said that he remembers them being up and latched. If they were not latched they would be hanging down. I cannot say for certain if the forward and mid latches were secured; only that they appeared to be. After we released the airplane for service; tug moved Aircraft X to a gate. If the latches were not properly secured; they should have perhaps fallen in the move but maybe they were jammed in the up position and did not fall. That's the only thing I can speculate as to what may have happened. Supplemental information from ACN 816911: Aircraft was due #1 Engine Mount Isolator Inspection. #1 Engine Fan Cowls; Reverser Cowls; and Core Cowls were opened for the inspection. The Inspection Boroscope Team performed the inspection of the engine mounts. When the Boroscope Inspection Team had completed the inspection; Mr. X and I closed the engine. Before we closed the Fan Cowls; Mr. X and I ensured all the latches were latched and secured on the Reverser Cowls. Then Mr. X and I closed the Fan Cowls and Core Cowls; ensuring all latches were latched and secured. Supplemental information from ACN 816916: After a normal preflight and taxi out; we were cleared for takeoff. I was the Pilot Flying. Shortly after liftoff; another aircraft reported to the Tower that our left engine lost what appeared to be a part of our unpainted engine cowling as we were on our takeoff roll. We switched to Departure and I had the First Officer request from ATC a leveloff at 5000 ft MSL and radar vectors. I called for the gear and flaps to up; kept the aircraft at clean maneuvering speed; engaged the autopilot; called for the after takeoff checklist; then transferred control of the aircraft and radios to the First Officer. There had been no abnormal handling issues or abnormal engine indications during the takeoff roll or after liftoff. I called the cabin and told the head Flight Attendant what had been reported to us and asked him to walk back and take a look at the left engine cowling area. He reported back to me that the unpainted portion of the engine cowling on the tail cone section of the left engine was damaged and mostly gone. I told him we would be returning; making a normal approach and lndg and would be on the ground in approximately 10 minutes; and that I would make a Public Announcement to the passengers after I spoke with Maintenance and Dispatch. After consulting with Maintenance and Flight Control; the decision to return was agreed upon by all 3 parties. I did not see a need to declare an emergency; since there were no abnormal handling issues or abnormal engine indications. I made a Public Announcement to the passengers that we were making a precautionary return due to the loss of some engine cowling and assured them that the engine and aircraft were operating normally. We made a normal approach and landing and taxied the aircraft uneventfully to the gate. Upon initial inspection at the gate by maintenance; they were able to confirm that the unpainted portion of the cowling on the tail cone section had indeed departed the aircraft. It appeared that there was a hole in part of the honeycombed section aft of the cowling on the bottom side of the tail cone and possibly some minor damage to the trailing edge flap directly aft of the left engine. Maintenance was unable to determine yet at that point if the fastener latches had failed or had not been properly latched and secured (several pieces of the cowling had been retrieved by airport operations). The First Officer; who had conducted the preflight inspection; was adamant that the latches had at least appeared to be fastened and secured during his walkaround. Supplemental information from ACN 817570: I was the First Officer and initially pilot monitoring the flight. Preflight including briefings and the aircraft walkaround was completed and no abnormalities were detected. The aircraft was boarded and dispatched routinely. Callback conversation with reporter ACN 816910 revealed the following information: Reporter stated the inboard and outboard core cowls on #1 engine basically ripped away from the lower aft latch; shortly after takeoff. There are three latches that are used to secure the core cowl. Part of the cowling was still attached to the cowl upper hinge line on the engine pylon of the B757-200.

Data retrieved from NASA's ASRS site as of May 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.