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Air Force officials have publicly insisted that a malfunction in a computerlike device called a synchrophaser cannot cause multiple-engine failure on a C-130 plane. But the Air Force's own documents say otherwise. |
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From: AUTODIN Message Traffic To: ACC/SE MESSAGE TRAFFIC Subject: C-130E, HAP, POWER ROLL-BACK, PRELIMINARY REPORT, Date: Tuesday, July 15, 1997 1:51PM ROUTINE R 142016Z JUL 97 FM 314 AW LITTLE ROCK AFB AR//SE//
SUBJECT: C-130E, HAP, POWER ROLL-BACK, PRELIMINARY REPORT, 19970505, NKAK, 001H 1. CONDITION REPORTED: THREE ENGINE ROLL-BACK
2. DATE AND TIME OF MISHAP: 19970505, 1225, DAY
3. BASE SUBMITTING REPORT: NKAK 3.1. WAS MISHAP ON BASE: NO MISHAP
4. DUTY STATUS: ON DUTY
5. NAME OF NEAREST BASE TO MISHAP: PETERSON AFB, CO
6. LOCATION OF MISHAP: COLORADO SPRINGS, CO 6.1. LAT/LONG OF BASE: 3848.4N/10442.1W
7. OBJECT INFORMATION: 7.1. NOMENCLATURE: C-130E THREE ENGINE ROLL-BACK ON AIRCRAFT MODIFIED BY TCTO lC-130-1486, ELECTRICAL SYSTEMS UPGRADE (ESU) 7.1.1. AIRCRAFT S/N: 64-0542 7.2. MAJCOM: AETC 7.2.1. NAF: l9TH AF 7.2.2. WING: 314 AIRLIFT WING, LITTLE ROCK AFB 7.2.3. SQUADRON: 53 AIRLIFT SQUADRON 7.3. WAS MISHAP WITHIN 10NM OF BASE? YES 7.4. WAS OBJECT DESTROYED? NO. NO DAMAGE. 8. PERSONNEL INFORMATION. 8.1. ALL PERSONNEL UNINJURED. 8.2. INJURY CLASS AND TYPE: N/A 8.3. EJECTION ATTEMPT N/A 8.4. CREWMEMBER STATISTICS N/A. TOXICOLOGY TESTING N/A. 9. NARRATIVE: 9.1. THE MISHAP AIRCRAFT (MA) DEPARTED PETERSON AFB, COLORDO, ON A HIGH DENSITY ALTITUDE COMBAT TRAINING MISSION. APPROXIMATELY 10 SECONDS AFTER TAKEOFF, NUMBERS ONE, THREE, AND FOUR ENGINE RPM DECREASED TO 97-96 PERCENT EACH (CONFIRMED BY THE FREQUENCY METER); TURBINE INLET TEMPERATURE (TIT) DECREASED 20-30 DEGREES; AND TORQUE FLUCTUATED 1000-2000 INCH POUNDS. THE MISHAP CREW (MC) IMMEDIATELY PLACED ALL FOUR PROPELLERS IN MECHANICAL GOVERNING, AND THE RPMS ALL RETURNED TO 100 PERCENT. THE MC THEN CLIMBED TO 10,000 FEET AGL TO FURTHER TROUBLESHOOT THE PROBLEM. THE MC PLACED NUMBER THREE PROPELLER BACK TO NORMAL GOVERNING, AND ITS RPM DECREASED TO 96 PERCENT. THE MC THEN RETURNED NUMBER THREE PROPELLER TO MECHANICAL GOVERNING, FOLLOWED THE "FOUR ENGINE POWER LOSS" CHECKLIST IAW SECTION III OF T.O. lC-130B-l AND RETURNED TO PETERSON AFB FOR AN UNEVENTFUL LANDING. NO OTHER MALFUNCTIONS WERE NOTED ON THE ESSENTIAL AC BUS OR ESSENTIAL AVIONICS AC BUS. 9.2. INVESTIGATION AND ANALYSIS. 9.2.1. MAINTENANCE (MX) PERSONNEL PERFORMED AN ENGINE RUN FOLLOWING THE MISHAP FLIGHT, AND RPMS WERE STILL LOW (IN NORMAL GOVERNING), READING 96%, 97%, AND 96% FOR ENGINES 1, 3, AND 4 RESPECTIVELY. THIS WAS BECAUSE THE SPEED BIAS MOTOR IN THE PROPELLER VALVE HOUSING MOVES WITH THE ELECTRICAL INPUTS FROM THE SYNCHROPHASER, AND STAYS AT THIS LAST POSITION. THEY DO NOT RESET THEMSELVES WHEN POWER IS REMOVED OR APPLIED. MX RESYCHRONIZED THE PROPELLERS AND THEY RETURNED TO NORMAL OPERATION. THE SYNCHROPHASER WAS REMOVED AND REPLACED. MX THEN PERFORMED ANOTHER ENGINE RUN WITH NO RECURRENCE OF ENGINE ROLL BACK. GENERATOR CONTACTOR UNITS (GCU) WERE CHECKED FOR POSSIBLE BIT CODES, AND NONE WERE FOUND. 9.2.2. THREE DAYS LATER THE AIRCRAFT RETURNED TO LITTLE ROCK WITH NO POWER ROLL BACKS. HOWEVER, THE MA DID EXPERIENCE A FLUCTUATION ON NUMBER 1 AND 3 TORQUE INDICATORS WITH NO OTHER ENGINE SYMPTOMS. TECHNICIANS FOUND BAD SPLICES AT FUSELAGE STATION 245 INVOLVING THE TORQUE METER INDICATION PICK-UP GOING TO THE DIGITAL FLIGHT DATA RECORDER (DFDR). THESE SPLICES WERE REPAIRED. 9.2.3. THE SYNCHROPHASER WAS SENT TO WARNER-ROBINS ALC FOR DR ANALYSIS, AND THE RESULTS SHOW THE SYNCHROPHASER TO BE WITHOUT FAULT. 9.2.4. A COPY OF THE DFDR TAPE WAS SENT FOR ANALYSIS. FOR 21 SECONDS JUST PRIOR TO THE MISHAP, THE DFDR WAS BLANK AND HAD SPURIOUS READOUTS, LIKE NUMBER 2 ENGINE BEING AT 199%, WHICH IS PHYSICALLY IMPOSSIBLE. THIS APPARENTLY IS NOT UNCOMMON SINCE THE RECORDING EQUIPMENT CAN MISS A TIME PERIOD WHEN THE AIRCRAFT IS EXPERIENCING A CHOPPY RIDE LIKE A TAKEOFF ROLL, WHICH THE MA HAD JUST COMPLETED. THE DFDR SHOWED ALL ENGINE PARAMETERS NORMAL UP TO THE POINT OF THE TAPE GOING BLANK. THE DFDR ALSO REVEALED THE TWO HF RADIOS WERE ON, BUT NOT TRANSMITTING IN THE MOMENTS BEFORE THE POWER ROLL BACK. 9.2.5. HF RADIO PROBLEMS OVER THE YEARS HAVE BEEN IDENTIFIED AS A SOURCE OF ROLL-BACKS DUE TO ELECTROMAGNETIC INDUCTION (EMI) INTO THE SYNCHROPHASER. THE INDUCED SIGNAL INTO THE SYNCHROPHASER CAUSES THE PROP BLADE ANGLES TO CHANGE WHICH REDUCES THE POWER. AS A RESULT OF THIS INTERFERENCE, A TCTO WAS PERFORMED ON ALL C-130S WHERE AN ALUMINUM SHIELD (STOVEPIPE) WAS PLACED AROUND THE HF ANTENNA CABLE AT THE LIGHTNING ARRESTOR TO REDUCE SPURIOUS EMI. DURING THE MISHAP FLIGHT, THE #l HF WAS OPERATING BUT WAS NOT KEYED DURING THE INCIDENT TIME FRAME. (IT IS WORTH NOTING THAT EVEN IF THE HF RADIO IS NOT TRANSMITTING, THE HF ANTENNA IS STILL RECEIVING A MINUTE AMOUNT OF POWER, BUT NOT NEARLY AS MUCH AS DURING A RADIO TRANSMISSION. THEREFORE IT IS UNLIKELY THAT AN HF ANTENNA CAN SHORT OUT IF IT BECOMES LOOSENED AND CONTACTS THE STOVEPIPE. THIS WOULD MOST LIKELY NOT CAUSE EMI WITH THE SYNCHROPHASER.) THE FLIGHT ENGINEER REQUESTED AN INSPECTION OF THE STOVEPIPE AT PETERSON AFB, BUT NOTHING WAS FOUND DURING THE VISUAL INSPECTION. WHEN THE AIRCRAFT RETURNED TO HOME STATION, THE ISSUE WAS REOPENED AND THE LIGHTNING ARRESTOR AND STOVEPIPE ASSEMBLY WERE DISASSEMBLED FOR A BETTER INSPECTION. A BROKEN #l HF ANTENNA CABLE WAS FOUND IN THE STOVEPIPE, AND THE STOVEPIPE HAD 7 OR 8 HOLES BURNED THROUGH IT. THE STOVEPIPE CAN'T PERFORM ITS INTENDED FUNCTION IF THE ANTENNA CABLE IS BROKEN OR INCORRECTLY INSTALLED. A NEW HF ANTENNA CABLE AND STOVEPIPE WERE INSTALLED. THE HF COUPLER AND R/T WERE BENCH CHECKED SERVICEABLE, BUT WERE REPLACED AS A PRECAUTIONARY MEASURE DUE TO THE SEVERITY OF THE PROBLEM. 9.2.6. A FOUR ENGINE RUN WAS PERFORMED TO ATTEMPT A DUPLICATION OF THE ROLL-BACK. THE #1 HF WAS INTERMITTENT, AND THE #2 HF WAS SO WEAK AS TO BE INOP. HOWEVER, WHEN #l HF WAS KEYED, ALL FOUR RPMS INCREASED, AND ALL FOUR TORQUEMETERS DECREASED. THE MOVEMENT WAS SMALL, BUT AIRLOAD ON THE PROPS IN FLIGHT MAGNIFY THIS SMALL CHANGE INTO A FULL ROLL-BACK. THIS SMALL CHANGE OCCURRED IN BOTH ESU SUPPLIED POWER AND NON-ESU (OR "DIRTY") POWER. THE ENGINES WERE SHUT DOWN TO TROUBLE SHOOT THE HF PROBLEMS AND THE NEWLY INSTALLED HF ANTENNA WAS FOUND INCORRECTLY INSTALLED. THE INSTALLATION PROCESS IS A BLIND MATING AND DIFFICULT TO ACHIEVE. THIS SITUATION BASICALLY ALLOWED US TO DUPLICATE THE ORIGINAL CONDITIONS THAT EXISTED ON THE AIRCRAFT DURING THE INFLIGHT ROLL-BACK. THE CABLE WAS INSTALLED CORRECTLY AND ANOTHER FOUR-ENGINE RUN WAS PERFORMED. THE ROLL-BACK COULD NO LONGER BE DUPLICATED, AND THE TORQUEMETER FLUX HAD DISAPPEARED. THE FLIGHT ENGINEER'S COMM CORD WAS FOUND TO BE INTERMITTENT AND CAUSING PROBLEMS DURING THE PROCESS. ALSO THE INTERPHONE BOX HAD TWO EACH BROKEN WIRES WHICH REQUIRED THE REPLACEMENT OF BOTH CANNON PLUGS. 9.2.7. STILL FURTHER TROUBLE SHOOTING REVEALED PROBLEMS BEHIND THE PILOT'S LOWER FORWARD CIRCUIT BREAKER (CB) PANEL. THE RADIO ESSENTIAL AC CIRCUIT BREAKER CONTACTS AND CONNECTING WIRES WERE FOUND TO BE LOOSE. THIS CB IS LOCATED BETWEEN THE AC INSTRUMENT AND FUEL CONTROL CB AND THE SYNCHROPHASER CB. OUR ELECTRICAL EXPERTS ASSERTED THAT IT WAS POSSIBLE THAT ELECTRICAL ARCING BETWEEN THE LOOSE CB CONTACTS COULD HAVE CAUSED EMI TO THE SYNCHROPHASER CB AND CIRCUIT. THIS IN TURN COULD ALSO HAVE CAUSED A POWER ROLL-BACK. 9.2.8. A ONE-TIME INSPECTION WAS CONDUCTED ON 62 ACTIVE DUTY C-130E AIRCRAFT ASSIGNED AT LITTLE ROCK FOR HF STOVEPIPE ASSEMBLY PROBLEMS. FIVE AIRCRAFT WERE FOUND TO HAVE DEFECTS, FOUR HAD UNSERVICEABLE STOVEPIPES, AND ONE HAD A MISSING ANTENNA ADAPTER. 9.2.9. IN THE FEW FLIGHTS THAT THE MA HAS FLOWN SINCE ITS IMPOUNDMENT, THERE HAVE BEEN NO FURTHER INCIDENTS OF POWER ROLL-BACKS. HOWEVER, THERE ARE STILL TORQUE METER INDICATION FLUCTUATIONS WHICH HAVE NOT BEEN RESOLVED ON NUMBERS 1 AND 3 ENGINES. WHENEVER THE ESU CIRCUITRY IS DISABLED FROM THE AIRCRAFT, THE TORQUE INDICATOR FLUCTUATIONS CEASE. WHENEVER DASH-7 TORQUE INDICATORS ARE USED WITH ESU POWER, THERE ARE NO INDICATION FLUCTUATIONS. BUT WHEN DASH-15 (MORE SENSITIVE) INDICATORS ARE INSTALLED, A 1,000IN-LB FLUCTUATION IS PRESENT ON NUMBERS 1 AND 3 INDICATORS WITH ESU-SUPPLIED POWER. THERE ARE NO OTHER FLUCTUATIONS (RPM, FUEL FLOW, AUDIBLE CUES) ACCOMPANYING THESE TORQUE INDICATOR FLUCTUATIONS, AS THE ENGINES KEEP RUNNING SMOOTHLY. 9.2.10. DEPOT ENGINEERS WlLL PROVIDE TECHNICAL ASSISTANCE WITH THE AIRCRAFT IN MID JULY. THE AIRCRAFT WILL UNDERGO ITS SCHEDULED ISO INSPECTION AND REMAIN GROUNDED IN THE MEANTIME. A FINAL MESSAGE WILL BE SENT AT THE CONCLUSION OF THIS SITUATION. 9.3. CONCLUSIONS. 9.3.1. ALL THE DISCOVERED EVIDENCE REVEAL THIS PARTICULAR ROLL-BACK WAS PROBABLY CAUSED BY ONE OR TWO THINGS, (EITHER ACTING SEPARATELY OR IN COMBINATION): THE BROKEN NUMBER ONE HF ANTENNA AND/OR THE LOOSE RADIO ESSENTIAL CB CONNECTIONS. EITHER OR BOTH OF THESE DISCREPANCIES COULD HAVE CAUSED EMI TO THE SYNCHROPHASER WHICH THEN COMMANDED A ROLL-BACK. THE AIRCRAFT FIT THE PARAMETERS FOR A TRADITIONAL SIMULTANEOUS ROLL-BACK, NOT A SEQUENTIAL ENGINE FAILURE. 9.3.2. THE C-130 AIRFRAME HAS HAD THESE ROLL-BACKS FOR MANY YEARS AND MODIFICATIONS HAVE BEEN PERFORMED TO HELP ALLEVIATE THIS SERIOUS CONDITION. A CONSTANT VOLTAGE REGULATOR WAS INSTALLED TO PROTECT THE SYNCHROPHASER FROM SPIKE VOLTAGES. THE STOVEPIPE WAS INSTALLED TO PREVENT HF EMI TO THE SYNCHROPHASER. A SOLID STATE SYNCHROPHASER WAS INSTALLED TO REDUCE THE ROLL-BACK. ALL OF THESE MODS HAVE REDUCED THE NUMBER OF ROLL-BACKS, BUT THEY WERE ONLY EXPECTED TO REDUCE THE NUMBER, NOT ELIMINATE THEM ENTIRELY. THE CAUSES OF ROLL-BACKS ARE NOT COMPLETELY KNOWN. THE VERY DESIGN OF A SYSTEM THAT HAS ONE BLACK BOX (THE SYNCHROPHASER) CONTROLLING OR INTERFERING WITH THE OPERATION OF ALL 4 ENGINES OPENS THE DOOR FOR PROBLEMS SUCH AS HAVE BEEN EXPERIENCED. A ROLL-BACK CAN BE CAUSED BY NORMAL SYNCHROPHASER FAILURE, BY GENERATOR FAILURE, BY PULSE GENERATOR FAILURE, BY GCU FAILURE, PROPELLER FAILURE, ENGINE FAILURE, OR BY WIRING PROBLEMS. THE ESU MODIFICATION WAS EXPECTED TO HELP BY PROVIDING CLEAN, STABLE POWER TO CONTROLLING EQUIPMENT. SO FAR, THE ROLE OF THE ESU MODIFICATION IN THIS INCIDENT IS INCONCLUSIVE AND IS YET TO BE DETERMINED. 9.4. FINDINGS. 9.4.1. FINDING 1. CAUSE. THE NUMBER ONE HF ANTENNA CABLE WAS BROKEN AND BURNED NUMEROUS HOLES IN ITS STOVEPIPE ASSEMBLY. (LOGISTICS, EQUIPMENT, ALC/LGM, FAULTY PART) 9.4.2. FINDING 2. THE RADIO ESSENTIAL AC CIRCUIT BREAKER, LOCATED ADJACENT TO THE SYNCHROPHASER CB, HAD LOOSE CONTACTS CAUSING POSSIBLE EMI TO THE SYNCHROPHASER. (LOGISTICS, EQUIPMENT, ALC/LGM, FAULTY PART) 9.4.3. FINDING 3. TEN SECONDS AFTER TAKEOFF, THE MA EXPERIENCED A THREE-ENGINE POWER ROLL-BACK. 9.4.4. FINDING 4. THE MC PLACED ALL FOUR PROPELLERS IN MECHANICAL GOVERNING, AND THE ROLL-BACK WAS CORRECTED. 9.4.5. FINDING 5. THE MC RETURNED NUMBER THREE PROPELLER TO NORMAL GOVERNING, AND ITS RPM DECREASED TO 96 PERCENT. 9.4.6. FINDING 6. THE MC PERFORMED THE "FOUR ENGINE POWER LOSS" CHECKLIST AND LANDED WITHOUT INCIDENT. 9.5. FINDINGS OF OTHER SIGNIFICANCE. 9.5.1. FINDING 1. THE HF ANTENNA INSTALLATION TO THE ANTENNA MOUNT IS A BLIND MATING (DONE BY FEEL ALONE) AND IS DIFFICULT TO ACHIEVE WITHOUT FAULT. 9.5.2. FINDING 2. TORQUE METER FLUCTUATIONS CAN BE CAUSED BY IMPROPER SPLICES OF THE TORQUE METER INDICATION PICK-UP TO THE DFDR AT FLIGHT STATION 245. 9.6. RECOMMENDATIONS. 9.6.1. RECOMMEND ALL C-130 UNITS EQUIPPED WITH THE EXTERNAL HF WIRE ANTENNA ASSEMBLY PERFORM A ONE-TIME INSPECTION OF THE HF STOVEPIPE ASSEMBLIES TO PREVENT POSSIBLE POWER ROLL BACK INCIDENTS. 9.6.2. RECOMMEND ALL C-130 UNITS PERFORM A ONE TIME INSPECTION OF THE INTEGRITY OF CIRCUIT BREAKERS (CB) SURROUNDING THE SYNCHROPHASER CB.
10. COGNIZANT OFFICIAL/OFFICE SYMBOL: MAJ RICHARD ROBICHAUD, 314 AW/SEF, DSN 731-3699, COMM. 501-988-3699 |
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