Narrative:

During flap retraction after takeoff from ZZZ; the airframe began to vibrate. As we accelerated; the vibration became worse. Captain and I decided to return to ZZZ. As flaps were extended; vibration stopped. On return; I noticed a map shift on ehsi. Didn't think too much about it at the time. We landed at 202.0 pounds which is an overweight landing. Landing was smooth and uneventful. We notified maintenance and they began their search for a cause. Having repaired what maintenance thought was the cause (a broken bracket on the left precooler outlet door); we re-boarded the aircraft and departed. On second takeoff; the same vibration returned with the same results. On return to the airport; I noticed another map shift that was somewhat larger than last takeoff. And on short final; the ground proximity stated 'too low; terrain; too low; terrain.' I triplechked the gear and flaps and all was as required for landing. Rest of landing was uneventful. Callback conversation with reporter revealed the following information: the reporter stated an attempt was made to find the cause of the vibration by using the maintenance computer but the correction had only a 1-LINE entry and appears the start of a narrative that was never finished. Maintenance does not report any findings or maintenance action taken to the reporting crews.

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Original NASA ASRS Text

Title: A B757-200 DURING FLAP RETRACTION HAD AIRFRAME VIBRATION. RETURNED TO DEP ARPT. FOUND L PRECOOLER DOOR BRACKET BROKEN. DEPARTED A SECOND TIME EXPERIENCED SAME VIBRATION. ON APCH HAD FALSE GND PROX WARNING. RETURNED TO DEP ARPT.

Narrative: DURING FLAP RETRACTION AFTER TKOF FROM ZZZ; THE AIRFRAME BEGAN TO VIBRATE. AS WE ACCELERATED; THE VIBRATION BECAME WORSE. CAPT AND I DECIDED TO RETURN TO ZZZ. AS FLAPS WERE EXTENDED; VIBRATION STOPPED. ON RETURN; I NOTICED A MAP SHIFT ON EHSI. DIDN'T THINK TOO MUCH ABOUT IT AT THE TIME. WE LANDED AT 202.0 LBS WHICH IS AN OVERWT LNDG. LNDG WAS SMOOTH AND UNEVENTFUL. WE NOTIFIED MAINT AND THEY BEGAN THEIR SEARCH FOR A CAUSE. HAVING REPAIRED WHAT MAINT THOUGHT WAS THE CAUSE (A BROKEN BRACKET ON THE L PRECOOLER OUTLET DOOR); WE RE-BOARDED THE ACFT AND DEPARTED. ON SECOND TKOF; THE SAME VIBRATION RETURNED WITH THE SAME RESULTS. ON RETURN TO THE ARPT; I NOTICED ANOTHER MAP SHIFT THAT WAS SOMEWHAT LARGER THAN LAST TKOF. AND ON SHORT FINAL; THE GND PROX STATED 'TOO LOW; TERRAIN; TOO LOW; TERRAIN.' I TRIPLECHKED THE GEAR AND FLAPS AND ALL WAS AS REQUIRED FOR LNDG. REST OF LNDG WAS UNEVENTFUL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED AN ATTEMPT WAS MADE TO FIND THE CAUSE OF THE VIBRATION BY USING THE MAINT COMPUTER BUT THE CORRECTION HAD ONLY A 1-LINE ENTRY AND APPEARS THE START OF A NARRATIVE THAT WAS NEVER FINISHED. MAINT DOES NOT RPT ANY FINDINGS OR MAINT ACTION TAKEN TO THE RPTING CREWS.

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.