SKINNER AVIATION INC

RIGHT MAIN FUEL TANK (TIP TANK) AFT BULKHEAD (PN: 0823400-109) CRACKED IN UPPER RADIUS. THIS BULK HEAD IS AN EXTENSION OF THE AFT WING SPARE IS THE ONLY ONE OF 2 LOCATIONS THAT HOLD THE FUEL TANK ON THE AIRPLANE. THIS AIRPLANE HAS BEEN THROUGH COUNTLESS 100 HOUR INSPECTIONS AND I'M CERTAIN THAT THIS CRACK WAS NOT THERE LAST ANNUAL/100 HOUR INSPECTION 85.3 HOURS AGO. THIS IS THE THIRD FAILURE OF TIP TANK AFT BULKHEAD (BOTH SIDES) THAT I'VE FOUND ON 340A'S IN THE LAST SEVERAL YEARS. ALL IN THE SAME RADIUS. THIS NEEDS TO BECOME AN AD!!!! IT COULD BE EASILY OVERLOOKED BY SOMEONE WHO IS LESS THAN THOROUGH. I'VE FOUND THIS CRACK ON 340A'S WITH 4500 HOURS TOTAL TIME.

THE RIGHT MAIN GEAR IDLER BELL CRANK ASSY BROKE IN HALF. THE BREAK CAUSED THE INNER GEAR DOOR TO HANG FREE. THE POINT OF FAILURE HAD RUST IN THE CRACK. THE GEAR DOOR APPEARS TO HAVE CAUGHT ON THE FAIRING WHILE OPENING AND THAT IS WHAT ADDED THE STRESS TO THE BELL CRANK AND LEAD TO ITS FAILURE. THE GEAR/GEAR DOOR TENSIONS/ RIGGING HAD BEEN VERIFIED AT LAST ANNUAL INSPECTION 34 OPERATION HOURS PRIOR AND WAS WITHIN LIMITS.

CRACKED CRANK CASE. REMOVED ALL CYLINDERS DUE TO 4 BEING LOW COMPRESSION. 2 OTHER CYLINDERS WERE RECENTLY REPLACED BY PERSONS UNKNOWN AT EXACT TIME UNKNOWN. I FOUND 8130-3 FORMS FOR THE TWO REPLACED CYLINDERS(5&3) OPPOSITE THE CASE CRACK, DATED MARCH 1, 2019. AIRCRAFT WAS OWNED BY SUNWEST AVIATION OF SAN LUIS OBISBO AT THE TIME. THE CRACK WOULD NOT HAVE BEEN VISIBLE AT PREVIOUS CYLINDER REPLACEMENT AS THE CRANKSHAFT OBSTRUCTED THE VIEW. THE CRACK STARTED AT THE MAIN BEARING BETWEEN #6 AND # 4 CYLINDERS. THIS WOULD HAVE LEAD TO CATASTROPHIC FAILURE IF IT HAD NOT BEEN DISCOVERED BY CHANCE. THE CRACK WAS BEGINNING TO BECOME VISIBLE FROM THE OUTSIDE BUT WAS IN A LOCATION THAT WAS HIDDEN BY BAFFLING. I DISSASEBLED THE ENTIRE ENGINE AND FOUND BEARING DAMAGE CAUSED BY DEBRIS. ENGINE IS MODIFIED TO A RAM7 AND HAS 873.6 HOURS SINCE OVERHAUL IN 2014 BY RAM. THIS ENGINE HAS NO RECORD OF FUEL FLOWS BEING SET UP AS REQUIRED BY TCM SB 97-3 AND WAS RUNNING VERY LEAN. WE SUSPECT THAT WHATEVER CAUSED THE 2 CYLINDERS TO BE REPALCED IN MARCH CAUSED THE CRACK AT THAT TIME.

LEFT MAIN FUEL TANK (TIP TANK) AFT BULKHEAD (PN: 0823400-109) CRACKED IN UPPER RADIUS. THIS BULK HEAD IS AN EXTENSION OF THE AFT WING SPARE AND IS ONE OF ONLY 2 LOCATIONS THAT HOLD THE FUEL TANK ON THE AIRPLANE. WE HAVE JUST PURCHASED THE AIRPLANE AND ONLY FLEW IT ONCE TO GET IT BACK TO OUR SHOP WERE WE DISCOVERED THE CRACK UPON INSPECTION. THIS IS THE 2ND 340A WHERE I HAVE SEEN THIS FAILURE, THE OTHER ONE WAS THE SAME BULKHEAD, SAME RADIUS BUT ON THE RIGHT TANK.

ENGINE FAILURE OVER OLD GROWTH FOREST. THE ENGINE HAD A LOUD BANG AND STARTED RUNNING VERY ROUGH ACCORDING TO PILOT. THE ENGINE SHOOK JUST AS BADLY WHILE OFF AND WINDMILLING AS IT DID WHEN THE ENGINE WAS RUNNING. PILOT LANDED AIRCRAFT IN A SWAMP WITH HEAVY DAMAGE TO THE PROP AND AIRFRAME. NO INJURIES. PILOT AND ONE PASSENGER ON BOARD. ENGINE WAS REMOVED PER NTSB AND FAA TO BE INSPECTED BY MANUFACTURER. THE CASE HAD A HOLE UNDER THE #6 CYLINDER BETWEEN BOTH PUSH ROD TUBES.