N821MH

ATA 2913

DURING ROUTINE INSPECTION, A HYDRAULIC FLUID LEAK WAS NOTED ON THE BELT DRIVEN HYDRAULIC PUMP DRIVE AND A PREVIOUSLY REPAIRED YELLOW TAGGED PUMP ASSEMBLY INSTALLED. THE REPLACEMENT PUMP DRIVE SHAFT LIP SEAL HAD BEEN REPLACED AS PART OF THE REPAIR. A NORMAL GROUND RUN AND LEAK CHECK WAS PERFORMED WITH NO DISCREPANCY NOTED. DURING THE OPERATIONAL CHECK FLIGHT THE CREW NOTED THE ILLUMINATION OF THE HYDRAULIC PRESSURE LOSS SEGMENT ON THE CAUTION WARNING PANEL AND PERFORMED AN IMMEDIATE PRECAUTIONARY LANDING. FOLLOWING AIRCRAFT SHUTDOWN AN EXAMINATION OF THE DUAL HYDRAULIC SYSTEM WAS PERFORMED. IT WAS EVIDENT THAT THE BELT DRIVEN HYDRAULIC PUMP INTERNAL “O” RING SEALING OR DRIVE SHAFT LIP SEAL HAD FAILED DURING OPERATION AND THAT THE BELT DRIVEN PORTION OF THE DUAL HYDRAULIC SYSTEM HAD SUFFERED A TOTAL LOSS OF HYDRAULIC FLUID. THE SECONDARY PORTION OF THE DUAL HYDRAULIC SYSTEM, THE MAIN GEAR BOX DRIVEN PUMP AND IT’S FLUID RESERVOIR WERE FOUND IN SERVICEABLE AND FULLY SERVICED CONDITION. ALL FLUID RESIDUE WAS CLEANED AS REQUIRED. A SERVICEABLE REPLACEMENT BELT DRIVEN HYDRAULIC PUMP WAS INSTALLED AND THE HYDRAULIC FLUID RESERVOIR SERVICED. GROUND RUN AND LEAK CHECK WAS SATISFACTORY AND THE AIRCRAFT OPERATIONAL CHECK FLIGHT COMPLETED WITH THE AIRCRAFT RETURNED TO SERVICE. THE DEFECTIVE PUMP WAS RETURNED TO THE SHOP FOR DETERMINATION OF LEAK FAILURE ROOT CAUSE. UP TO THIS DATE SEVERAL DOZEN ROUTINE DRIVE SHAFT LIP SEAL REPLACEMENTS WERE COMPLETED PER THE COMPONENT MAINTENANCE MANUAL PREVIOUSLY ON THIS MODEL HYDRAULIC PUMP IN OUR SHOP WITH ONLY MINOR LEAKAGE NOTED DUE TO SHAFT SEAL RUNNING FACE DETERIORATION. THESE PUMPS, WHEN INSTALLED AND FOUND TO BE LEAKING AFTER SEAL REPLACEMENT, ARE ROUTINELY DISCARDED AS BEYOND ECONOMICAL REPAIR. NO LEAK OF THIS MAGNITUDE HAS OCCURRED PREVIOUSLY IN OUR EXPERIENCE WITH THESE PUMPS.

ATA 5302

DURING PREFLIGHT INSP, A CRACK WAS DISCOVERED RADIATING FROM THE INSIDE LOWER AFT RT CORNER OF THE TAIL BOOM TAIL CONE CUTOUT FOR THE HORIZ STABILIZER. AN OVER LYING DOUBLER WAS NOT CRACKED AND OBSCURED THE CRACK FROM EASY VIEWING. WITH THE HORIZ STABILIZER REMOVED THE CRACK WAS EASILY VIEWED FROM THE LT SIDE OF THE TAIL BOOM LOOKING ACROSS THE TAIL BOOM INTERIOR. AN APPROVED REPAIR FROM THE MFG IS BEING APPLIED THAT HAS AN EXTENSION ON THE DOUBLER THAT REINFORCES THE TAIL BOOM CUTOUT INSIDE CORNER. THE DOUBLER HAS BEEN REMOVED AND THE TAIL CONE CRACK LENGTH MEASURED JUST OVER 1.5 INCH IN LENGTH. A STOP DRILL HAS BEEN APPLIED TO THE CRACK AND THE DOUBLER MFG AND INSTALLED IAW APPROVED DATA. NEWLY DELIVERED TAIL BOOMS NOW HAVE DOUBLERS EXTENDING BOTH ABOVE AND BELOW THE HORIZONTAL STABILIZER CUT OUTS TO HELP PREVENT CRACK DEVELOPMENT.

ATA 6220

DURING ROUTINE MX INSPECTION 1 OF THE 3 FRQUENCY ADAPTERS FOUND TO HAVE A CRACK IN THE ELASTOMER NEARING ITS MAXIMUM ALLOWABLE LIMITATION OF 10MM. A NEW KIT OF 3 MATCHED ADAPTERS WERE INSTALLED.

ATA 6797

FAILURE CODE AT SHUTDOWN INDICATED FAULT WITH THE COLLECTIVE POTENTIOMETER. A NEW POTENTIOMETER WAS INSTALLED AND NO FURTHER DEFECT REPORTED. IT WAS RECENTLY DISCOVERED THAT THE ROUTING OF AIR CONDITIONING SYSTEM WIRING IN CONTACT WITH THE UNSHIELDED ELECTRICAL HARNESS FOR THE POTENTIOMETER WAS CAUSING SPURIOUS SIGNALS IN THE CONTROL DATA WHICH WERE INTERPRETED AS A PONTENTIOMETER FAILURE. DOZENS OF THESE PONTENTIOMETERS WERE REPLACED. REROUTING THE AIR CONDITIONING WIRING HAS ALMOST ENTIRELY ELIMINATED THE NEED TO REPLACE THESE POTENTIOMETERS. (K)

ATA 3150

POSITION LIGHTS FAILED TO ILLUMINATE WITH CB NOT POPPED AND NO APPARENT SHORTS FOUND. INVESTIGATION REVEALED CIRCUIT TRACE ON THE PCB SUPPLYING POWER TO THE POSITION LIGHT SWITCH HAD MELTED/BLOWN LIKE A FUSE. THIS A COMMON PROBLEM FOR THIS PART. SUGGEST MORE ROBUST TRACE BE APPLIED TO PCB CIRCUIT. REDUCTION OF CB AMPERAGE PROTECTION VALUE OR A REDESIGN OF CIRCUIT WHICH MAY BE FAULTY. (K)

ATA 6220

DURING ROUTINE INSP, SPACER WAS FOUND WITH EXCESSIVE WEAR AT ENDS WHERE IT MAKES SCISSOR LINK BUSHING CONTACT. POSSIBLE DIRT ACCUMULATION IN THE GREASE WAS A FACTOR IN THE WEAR. THIS IS A COMMON FAILURE FOR THIS PART. SUGGEST THIS PART BE KEPT CLEAN IN SANDY ENVIRONMENTS. (K)

ATA 5551

DURING ROUTINE INSP FITTING WAS FOUND CRACKED IN (2) PIECES. NEW FITTING WAS INSTALLED. THIS IS A COMMON FAILURE FOR THIS PART. PART MAY HAVE BEEN SHIMMED INCORRECTLY OR BORE HOLE NOT ALIGNED PERFECTLY. SUGGEST A MORE DURABLE MATERIAL BE USED IN THIS PARTS MFG SUCH AS TITANIUM OR SS AS ALUMINUM ALLOY FAILS ROUTINELY UNDER NORMAL STRESS APPLIED TO THIS PART. (K)

ATA 5344

(REF 0429084134) DURING ROUTINE INSPECTION, HINGE WAS FOUND CRACKED THROUGH TO SCREW MOUNTING BORES TO THE METALS EDGE. THIS IS A VERY COMMON FAILURE FOR THIS PART. SUGGEST PART BE MFG OF MORE DURABLE MATERIAL SUCH AS STAINLESS STEEL. (K)

ATA 6220

(REF 0429084134) DURING ROUTINE INSPECTION, THE ELASTOMER ON (1) FREQUENCY ADAPTER WAS FOUND CRACKED. A NEW SET OF (3) ADAPTERS WAS INSTALLED. THIS IS A VERY COMMON DEFECT FOR THIS PART. SUGGEST A DIFFERENT ELASTOMER FORMULATION BE UTILIZED. AN OLDER PN FREQUENCY ADAPTER HAD A FORMULATION THAT RARELY FAILED. THE MFG IS HAVING DIFFICULTY PRODUCING ENOUGH OF THESE FAILURE PRONE PART TO MEET DEMAND. RETURNING TO THE OLDER FORMULATION HAS BEEN SUGGESTED TO THE AC MFG FOR YEARS WITH O ACTION TAKEN.

ATA 5344

DURING ROUTINE INSPECTION A CRACK WAS FOUND IN THE HINGE MOUNTING FLANGE RADIATING FROM THE OUTERMOST LT ATTACHMENT SCREW BORE. REMOVAL OF ATTACHMENT SCREW REVEALED THE FLANGE CORNER HAD SEPARATED FROM THE REST OF THE HINGE. THIS IS A VERY COMMON FAILURE FOR THIS PART. A MORE DURABLE MATERIAL SUCH AS SS OR TITANIUM MAY BE REQUIRED. (K)

ATA 5200

THIS PART CALLED A SHOCK ABSORBER DEVICE BY THE MFG IS USED TO SEQUENCE THE DOOR LATCHING MECHANISM TO PREVENT DOOR CLOSURE WITH LATCH PINS EXTENDED AND IMPACTS WITH THE DOOR FRAME. IT IS MFG OF A VERY BRITTLE BRONZE TYPE MATERIAL THAT WILL CRACK WITH JUST THE INSTALLATION OF BLIND RIVETS IN THE COUNTERSUNK HOLES PREDRILLED IN THE PART. CRACKS WERE FOUND EMANITING FROM THE HOLES AT THE RIVETS WITH A CORNER OF THE MOUNTING FLANGE FOUND MISSING. SUGGEST THIS PART BE MFG FROM STAINLESS STEEL FOR BETTER DURABILITY. (K)