A B767 IN CLB AT FL280 HAD THE R AIR CONDITIONING PACK ACCESS DOOR DEPART THE ACFT. MAINT WORK DONE PRIOR TO DEP ON R PACK.

Narrative

PRIOR TO DEP OF FLT X; MAINT WAS INVESTIGATING R PACK OP AND SUBSEQUENTLY PLACARDED THE R PACK INOP. I NOTIFIED DISPATCH PER MEL ADVANCED NOTIFICATION PROC OF SINGLE PACK OP. WHEN MAINT COMPLETE; I PERSONALLY INSPECTED THE PACK ACCESS DOOR WAS CLOSED AND VISUALLY THAT ALL LATCHES WERE LATCHED PRIOR TO DEP. IN CLB TO FL310 (INTERMEDIATE ALT) JUST PAST LA BELLE (LBV) PRIOR TO SARASOTA ON J-86 AT FL280 AND 305 KTS; ACFT EXPERIENCED A THUD FOLLOWED BY A VIBRATION. FLT ATTENDANTS INFORMED ME OF ABNORMAL VIBRATION MOST PRONOUNCED IN BUSINESS CLASS FLOOR SECTION OF THE ACFT. I DIRECTED ACR X AIRLINES PLT JUMP SEAT RIDER TO INVESTIGATE FLT ATTENDANT'S RPT. PLT CONFIRMED FLT ATTENDANT'S RPT STATING THE VIBRATION WAS MORE PRONOUNCED IN BUSINESS CLASS. DECLARED EMER TO ZJX AND REQUESTED RETURN TO ZZZ. NOTIFIED DISPATCH VIA ACARS OF RETURN TO ZZZ DUE TO ACFT VIBRATION. DSNDED TO FL240 AND SLOWED TO 240 KTS ON RETURN TO ZZZ. VIBRATION WAS REDUCED AT THE LOWER ALT AND DECREASED AIRSPD. REQUESTED ARFF AS PRECAUTION AND VISUAL INSPECTION UPON LNDG. REQUESTED AND LANDED ON RWY 9R (13000 FT) AT 278500 LBS (500 LBS OVERWEIGHT). LNDG AND TOUCHDOWN WAS SMOOTH. POSTFLT MAINT INSPECTION FOUND R PACK ACCESS DOOR MISSING FROM ACFT.