RPTR IN CRUISE EXPERIENCES MYSTERIOUS SUDDEN CONTINUOUS SHUDDER IN THE AIRFRAME AND LEARNS ON INVESTIGATION AT THE GATE THE SKIN IS DELAMINATING FROM AN UPPER WING PANEL.

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MY FO WAS FLYING THE BEECH 1900D ACFT DURING A ROUTINE REPOSITIONING FLT BTWN BRADFORD; PA (BFD) AND JAMESTOWN; NY (JHW). CONDITIONS WERE VFR WITH NO TURB; AND THE ACFT WAS IN STRAIGHT AND LEVEL FLT AT PUBLISHED RECOMMENDED PWR SETTINGS. NO PAX WERE ABOARD. A SUDDEN; CONTINUOUS SHUDDER WAS FELT IN THE AIRFRAME. ALL ENG INSTS AND SYS APPEARED NORMAL. VIEWING FROM THE COCKPIT WINDOWS; A VISUAL INSPECTION OF THE WINGS; NACELLES; PROPS AND SPINNERS REVEALED NOTHING ABNORMAL. I INDICATED TO THE FO THAT I WAS TAKING CTL OF THE ACFT. REDUCING THE PWR DID NOT IMMEDIATELY STOP THE SHUDDERING; BUT THE SUBSEQUENT REDUCTION IN AIRSPD DID SEEM TO LESSEN THE SEVERITY OF THE VIBRATION. CTL OF THE ACT WAS NORMAL; AND WE CONTINUED ON TO JHW; LESS THAN 10 NM AWAY. EMER PROCS WERE CONSULTED AND COMPLIED WITH AS APPROPRIATE; AS WERE ALL NORMAL CHKLIST ITEMS. EXTENSION OF LNDG GEAR AND FLAPS WAS NORMAL; AND THE ACFT WAS LANDED UNEVENTFULLY. BECAUSE OF THE BRIEF TIME (LESS THAN 5 MINS) BTWN THE ONSET OF VIBRATION AND THE LNDG AT JHW; AND THE NORMAL FLT CHARACTERISTICS OF THE ACFT; NO ATTEMPT WAS MADE TO DECLARE AN EMER. PRIOR TO ENG SHUTDOWN; A STANDARD RUNUP WAS PERFORMED; WITH ALL SYS CHKING NORMAL. UPON EXITING THE ACFT; THE PROB WAS IMMEDIATELY APPARENT: A 3 FT BY 2 FT (APPROX) SECTION OF ALUMINUM FROM THE UPPER SURFACE OF THE L WING INBOARD OF THE NACELLE HAD SEPARATED FROM THE WING IMMEDIATELY AFT OF THE LEADING EDGE DEICE BOOT; AND HAD PEELED BACKWARD. IT REMAINED ATTACHED TO THE WING; STICKING UP NEARLY VERT. CLOSER INSPECTION REVEALED THAT THE ALUMINUM SHEET WAS GLUED TO A HONEYCOMB STRUCTURE UNDERNEATH; AND HAD DELAMINATED AS AN APPARENT RESULT OF FAILURE OF THE ADHESIVE BONDING THE 2 TOGETHER. THIS SECTION IS A PANEL THAT PROVIDES ACCESS TO THE AIR CYCLE MACHINE. THIS ACFT IS FAIRLY NEW; HAVING ABOUT 500 HRS AND 1100 CYCLES SINCE NEW. THE CHIEF PLT; FLT FOLLOWING; AND MAINT WERE IMMEDIATELY CONTACTED; AND THE EVENT WAS NOTED IN THE ACFT'S DISCREPANCY LOG. I WOULD ADVISE THAT OTHER BEECH 1900 ACFT BE INSPECTED FOR SIMILAR DEFECTS; AS IT APPEARED THAT THE GLUE USED PROVIDED A VERY WEAK BOND; AND WAS EASILY PEELED AWAY BY HAND. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: HE DID NOT KNOW IF THERE WERE ANY 'A' MODELS; AND TO HIS KNOWLEDGE THERE ARE VERY FEW 'B' MODELS; AND HIS AIRPLANE IS GETTING RID OF MOST OF THEIR 'C' MODELS. THE PANEL SIZE LOOKS THE SAME; AND THE CONSTRUCTION LOOKS THE SAME BUT HE DOUBTS THE PART IS INTERCHANGEABLE BTWN THE D AND C. THERE WAS NO MAINT RECENTLY HE KNEW ABOUT ON THE AIR CYCLE MACHINE ON THIS AIRPLANE. HE WAS WALKING THROUGH THE HANGAR LAST MONTH AND SAW THE LEADING EDGE REMOVED FOR A BLEED LINE MODIFICATION. THE RUBBER DEICE BOOT TRAILING EDGE IS ABOUT 6 INCHES FORWARD OF THE PANEL. THE THOUGHT OCCURRED THAT EXCESSIVE HEAT CAUSED THE FAILURE OF THE GLUE. THERE WAS NO EVIDENCE OF THIS. THE RPTR HAS BEEN WORKING WITH COMPOSITES AND THE APPEARANCE TO HIM WAS THE PREPARATION WAS CORRECT BUT THE MIX OF THE HARDENER AND EPOXY WAS SUCH THAT THERE WAS VERY LITTLE ADHESIVE QUALITY TO EITHER HONEYCOMB OR THE METAL. THE PANEL SIZE IS ABOUT 3 FT SPAN WISE AND 2 FT CHORD WISE. MOST OF THE PANEL REMAINED WITH THE AIRPLANE AND THOSE PIECES THAT BROKE OFF WERE ABOUT THE SIZE OF YOUR HAND. THIS WAS ALL THE TOP SURFACE OF THE PANEL THAT COVERS THE AIR CYCLE MACHINE. THE THOUGHT THAT THE AIR CYCLE MACHINE GOT HOT AND COOKED THE GLUE WAS ADDRESSED AND REJECTED AS THERE WAS NO INDICATION OF THAT ON THIS RELATIVELY NEW AIRPLANE. BIRDS WERE THOUGHT OF AND THERE WAS NO INDICATION OF BIRD STRIKE PROBS. THE AIRPLANE DOES HAVE A FLT RECORDER AND THE PLTS WANTED THE TAPES PULLED; BUT; THE COMPANY WANTED TO GET THE AIRPLANE PANEL REPLACED AND ON ITS WAY. THE RPTR SAID THE SPD WAS ABOUT 215 KIAS AS THEY WERE AT AN UNCTLED ARPT AND USUALLY OPERATE A LITTLE SLOWER THAN AT CTLED ARPTS. THE AIRSPD REDLINE IS ABOUT 254 KTS AND THEY DID NOT COME CLOSE TO THAT SPD ON THIS FLT. THE RPTR SAID THERE IS NOTHING HE WOULD DO DIFFERENTLY WERE IT TO HAPPEN AGAIN. OTHER THAN BE A LITTLE QUICKER TO TAKE CTL FROM FO AND SLOW THE AIRPLANE UP A LITTLE SOONER. ON THE PREFLT THE CONDITION OF THE GLUE WOULD NOT BE VISIBLE EVEN IF YOU KNEW WHERE TO LOOK WITHOUT REMOVING THE PANEL WHICH IS ATTACHED WITH ABOUT 60 SCREWS. SOME KIND OF ULTRA SOUND TEST MIGHT SHOW THE FLAW.