FLC OF ACR LTT ACFT EXPERIENCED AN ACFT VIBRATION CAUSED BY A LOOSE WING PANEL AND RETURNED TO BASE.

Narrative

FLT LEFT THE GATE AT PM39 LCL; HEADED FOR RWY 26 FOR TKOF. SHORTLY AFTER TKOF; WHILE IN A CLBING R TURN; THE FO; WHO WAS FLYING; RPTED TO ME SOME VIBRATIONS IN THE CTL COLUMN WHILE PASSING. THROUGH 2500 FT THE HANDLING OF THE AIRPLANE WAS NOT AFFECTED NEGATIVELY; HOWEVER; THE VIBRATIONS COULD BE FELT ALL THE WAY THROUGH THE AIRPLANE. WE LEVELED OFF AND SLOWED DOWN THE AIRPLANE TO 160 KTS. I LOOKED TOWARD THE L ENG AND PROP AND NOTICED A PIECE OF METAL ON THE OUTBOARD OF THE L WING FLAPPING UP AND DOWN ON TOP OF THE WING. WE PROCEEDED TO RETURN TO IAH FOR LNDG. THE APCH AND LNDG WERE UNEVENTFUL AND NORMAL. NO EMER WAS DECLARED SINCE THERE WAS NEVER ANY DOUBT IN THE OUTCOME OF A SAFE LNDG. THE POST-FLT INSPECTION REVEALED THAT THE INSPECTION PANEL BTWN THE L AILERON AND THE WING HAD 12 RETAINING SCREWS MISSING AND 2 STRIPPED. THEREFORE; ALLOWING ABOUT 2 FT OF THAT PANEL TO BE LOOSE AND FLAP UP AND DOWN ON TOP OF THE WING. THE AREA IS NOT VISIBLE DURING THE PREFLT INSPECTION DUE TO THE HEIGHT OF THE WING. THE AIRPLANE HAD JUST COME OUT OF MAINT; AND IT WAS THE FIRST FLT SINCE THE AIRPLANE HAD COME OUT OF THE HANGAR. THIS POSES SOME SERIOUS QUESTIONS ABOUT MAINT PROCS.