A B767-300ER CREW ON LEVEL OFF AT FL270 HEARD A 'THUMP' WITH SLIGHT WIND NOISE. ACFT FLEW NORMALLY WITH ALL INDICATIONS NORMAL. HAD LEFT LOWER AIR-CONDITIONING DOOR DEPART ACFT.

Narrative

ZZZ DEP; FL270 HEARD A 'BANG' AND THE PLANE SHOOK; SLIGHT WIND NOISE. NO WARNING LIGHTS; NO ABNORMAL FUEL/ENG INDICATIONS; AND PLANE FLEW NORMALLY WITH AUTOPLT OFF. AFTER LNDG IN YYY I FOUND OUT WE LOST AN AIR CONDITIONING PANEL APPROX 4 FT BY 8 FT. CAUSED DAMAGE TO SURROUNDING SKIN ON AIRPLANE AND LEFT INBOARD FLAP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED PART OF THE DOOR DEPARTED ON TKOF CLB AS THE L AND R INBOARD FLAPS AS WELL AS THE L AND R MAIN LNDG GEAR DOORS INCURRED DAMAGE. THE RPTR SAID AT FL270 THE REMAINDER OF THE DOOR DEPARTED THE AIRPLANE WITH A BIG 'THUMP' AND THE ONLY THING NOT NORMAL WAS A WIND NOISE. THE RPTR STATED THE 4 FT BY 8 FT DOOR WAS FOUND MISSING AND THE DAMAGE TO THE FLAPS AND LNDG GEAR DOORS WAS EXAMINED. THE RPTR SAID THE AIRPLANE HAD TO BE MAINT FERRIED TO THE MANUFACTURER GEAR DOWN DUE TO THE MAIN LNDG GEAR DOOR DAMAGE. THE RPTR STATED THE LNDG GEAR DOORS ON THIS AIRPLANE SERVE AS GEAR UP LOCKS. THE RPTR SAID THE AIRPLANE INCURRED A LONG OUT OF SVC TIME; BUT IS NOW BACK IN SVC. THE RPTR STATED THAT THE INVESTIGATION BY MAINT AND ENGINEERING FOUND THE DOOR LATCHES COULD BE FALSE LATCHED WITH NO VISUAL INDICATION OF BEING UNLOCKED. THE RPTR SAID THIS DOOR WAS OPENED AND CLOSED BY MAINT PRIOR TO DEP.