Narrative:

As we accelerated climbing thru 10;000 ft we felt and heard a vibration in the cockpit. All engine; hydraulics; electrical and pressurization indications were normal. There were no EICAS messages or warnings. The lead flight attendant soon called and said there was a bad vibration at mid cabin. We began to slow the aircraft and stopped the climb at FL190. There was a deadheading 767 check airman and I ask the flight attendant to put him on the phone. I asked him what he was experiencing and he said the same thing the flight attendant did; bad vibration and noise. We elected to return to [departure airport] but first we needed to burn fuel to get to maximum landing weight of 198;000. We entered a holding pattern at 16;000 ft with gear down; flaps 1; airspeed 210 and APU running to burn the fuel down. The 767 check airman was allowed into the cockpit in case he could offer assistance. Operations; maintenance; and dispatch were all advised that we were returning; along with the flight attendants and passengers. We declared an emergency just in case something happened on landing. After parking at gate it was discovered that a cover on a heat exchanger had ruptured. An inspection door right in front of the compartment where the heat exchanger is located was gone. There was some damage to the compartment door where the heat exchanger was located and damage to the underside of the aircraft where the inspection door was beating on the aircraft until it blew off. I assume the door was the source of the vibration.

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Original NASA ASRS Text

Title: B757-200 Captain reported significant vibration after takeoff. Flight returned to departure airport where an access door was found missing.

Narrative: As we accelerated climbing thru 10;000 FT we felt and heard a vibration in the cockpit. All engine; hydraulics; electrical and pressurization indications were normal. There were no EICAS messages or warnings. The Lead Flight Attendant soon called and said there was a bad vibration at mid cabin. We began to slow the aircraft and stopped the climb at FL190. There was a deadheading 767 Check Airman and I ask the Flight Attendant to put him on the phone. I asked him what he was experiencing and he said the same thing the Flight Attendant did; bad vibration and noise. We elected to return to [departure airport] but first we needed to burn fuel to get to maximum landing weight of 198;000. We entered a holding pattern at 16;000 FT with gear down; flaps 1; airspeed 210 and APU running to burn the fuel down. The 767 Check Airman was allowed into the cockpit in case he could offer assistance. Operations; Maintenance; and Dispatch were all advised that we were returning; along with the flight attendants and passengers. We declared an emergency just in case something happened on landing. After parking at gate it was discovered that a cover on a heat exchanger had ruptured. An inspection door right in front of the compartment where the heat exchanger is located was gone. There was some damage to the compartment door where the heat exchanger was located and damage to the underside of the aircraft where the inspection door was beating on the aircraft until it blew off. I assume the door was the source of the vibration.

Data retrieved from NASA's ASRS site 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.