Narrative:

The timing of the following events took place over a time span of less than 4 mins during a critical phase of flight. Some of the events occurred simultaneously with radio xmissions, confign changes, airspeed changes and constantly changing altitude. We were descending on a 7 mi base leg at 1500 ft AGL for runway 14R (13000 ft long) at ord IAP. Approach control cleared us for the visual approach and handed us off to ord tower. We selected flaps to 2 degrees while simultaneously checking in with ord tower. We were subsequently cleared to land on runway 14R. The flight engineer advised me that the #1 and #2 bus tie lights had illuminated along with an over/under excitation fault on the annunciator panel. A few seconds later, he announced that the #3 bus tie light was illuminated along with a phase imbalance fault on the enunciator panel. I visually checked the electrical panel to ascertain if essential power was protected and the busses were pwred. All electrical system were pwred to my satisfaction. I elected to continue the approach to landing. By this time we were configured with landing gear down and flaps selected to 15 degrees. I directed the flap extension to final landing setting in order to reduce our workload and emphasize the need to concentrate on the landing maneuver. Within seconds, I heard circuit breakers begin to pop. It sounded like a popcorn machine in that none popped simultaneously or in any particular sequence. The flight engineer advised that we were losing fuel boost pump electrical power due to popped circuit breakers. We were approximately 1000-800 ft AGL on the final approach by this time. He idented several other critical components which had been disabled due to circuit breakers popping. We lost the equipment cooling fan which led me to believe that a large number of flight instruments were in imminent danger of failure. I directed the flight engineer to reset the equipment cooling fan circuit breaker to restore cooling air to the flight instrumentation electronics bay. It held until shortly after touchdown when it popped again. During this sequence of events, I directed the flight engineer to check the hydraulic system and anti-skid to ensure that we had adequate hydraulic and braking system to successfully complete the landing. The landing was uneventful. We turned off the runway and proceeded to the gate. En route to the gate, we turned off all power to the flight instruments in order to keep the equipment from overheating because the equipment cooling fan circuit breaker had popped on landing rollout. Prior to engine shutdown at gate arrival, we noted that all of the generators were still pwring their respective busses and essential power was operating normally. Maintenance specialists met us to discuss the problems and subsequently took the aircraft out of service for further inspection and investigation. After further investigation at the gate, we noted that all of the equipment that we had lost was high load and, for the most part, motor driven. There were several failures associated with cabin lighting and landing light circuit breakers. Most of these failures were associated with the #3 generator buss. In spite of the seeming gravity of these failures, the electrical system performed exactly as I expected and continued to power the aircraft electrical busses. The load shedding we witnessed is consistent with the design of this very complicated system. The welfare and safety of this aircraft and occupants were my uppermost concern throughout this sequence of events. In the heat of the operation close to the ground, the captain and crew were faced with applying all of their training, utilizing all available assistance (ie, emergency procedure checklists), flying the airplane and successfully landing with a failing electrical system. What we learned from this event is that running the emergency procedures checklists may not be a classical situation where one has plenty of time for analysis and application of curative measures. That is why we 'train, train, train' to instill absolute knowledge of each aircraft system. One small mistake in this sequence of events could have produced a serious situation capable of threatening the safety of crew and passenger. The safety investigation is still incomplete as of this writing. Further details regarding equipment malfunctions that caused these failures will be revealed in an internal investigative process. Callback conversation with reporter revealed the following information: the captain was highly experienced in the aircraft and is an IOE and line check airman with his air carrier. After landing the aircraft was removed from service. The aircraft was then ferried to the air carrier's main engineering and maintenance base for extensive engineering analysis. The following was found: 1) the #3 generator lost one of the AC phases. This caused all high load items on #3 bus to begin random popping their circuit breakers. 2) this caused generators #1 and #2 to be removed from the tie bus. 3) the phase imbalance was caused by the dead phase on #3 generator. Boeing's long-time supplier of bus tie breakers is no longer manufacturing new units. A new vendor has started providing new units. After the incident, testing by boeing revealed that the breakers manufactured by the new vendor do not meet boeing specifications. All newly manufactured breakers in the incident aircraft were examined. All were found to have pitted contacts and showed signs of overheating. One had signs of a small internal fire. All new vendor generator control and bus tie breakers were replaced and no further aircraft problems have been reported. As parts become available, the air carrier is replacing all of the suspect breakers on its B727 fleet.

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Original NASA ASRS Text

Title: B727 CREW LOST MULTIPLE ELECTRICAL COMPONENTS AND HAD FAULTS ON ALL 3 ACFT GENERATORS DURING LNDG APCH.

Narrative: THE TIMING OF THE FOLLOWING EVENTS TOOK PLACE OVER A TIME SPAN OF LESS THAN 4 MINS DURING A CRITICAL PHASE OF FLT. SOME OF THE EVENTS OCCURRED SIMULTANEOUSLY WITH RADIO XMISSIONS, CONFIGN CHANGES, AIRSPD CHANGES AND CONSTANTLY CHANGING ALT. WE WERE DSNDING ON A 7 MI BASE LEG AT 1500 FT AGL FOR RWY 14R (13000 FT LONG) AT ORD IAP. APCH CTL CLRED US FOR THE VISUAL APCH AND HANDED US OFF TO ORD TWR. WE SELECTED FLAPS TO 2 DEGS WHILE SIMULTANEOUSLY CHKING IN WITH ORD TWR. WE WERE SUBSEQUENTLY CLRED TO LAND ON RWY 14R. THE FE ADVISED ME THAT THE #1 AND #2 BUS TIE LIGHTS HAD ILLUMINATED ALONG WITH AN OVER/UNDER EXCITATION FAULT ON THE ANNUNCIATOR PANEL. A FEW SECONDS LATER, HE ANNOUNCED THAT THE #3 BUS TIE LIGHT WAS ILLUMINATED ALONG WITH A PHASE IMBALANCE FAULT ON THE ENUNCIATOR PANEL. I VISUALLY CHKED THE ELECTRICAL PANEL TO ASCERTAIN IF ESSENTIAL PWR WAS PROTECTED AND THE BUSSES WERE PWRED. ALL ELECTRICAL SYS WERE PWRED TO MY SATISFACTION. I ELECTED TO CONTINUE THE APCH TO LNDG. BY THIS TIME WE WERE CONFIGURED WITH LNDG GEAR DOWN AND FLAPS SELECTED TO 15 DEGS. I DIRECTED THE FLAP EXTENSION TO FINAL LNDG SETTING IN ORDER TO REDUCE OUR WORKLOAD AND EMPHASIZE THE NEED TO CONCENTRATE ON THE LNDG MANEUVER. WITHIN SECONDS, I HEARD CIRCUIT BREAKERS BEGIN TO POP. IT SOUNDED LIKE A POPCORN MACHINE IN THAT NONE POPPED SIMULTANEOUSLY OR IN ANY PARTICULAR SEQUENCE. THE FE ADVISED THAT WE WERE LOSING FUEL BOOST PUMP ELECTRICAL PWR DUE TO POPPED CIRCUIT BREAKERS. WE WERE APPROX 1000-800 FT AGL ON THE FINAL APCH BY THIS TIME. HE IDENTED SEVERAL OTHER CRITICAL COMPONENTS WHICH HAD BEEN DISABLED DUE TO CIRCUIT BREAKERS POPPING. WE LOST THE EQUIP COOLING FAN WHICH LED ME TO BELIEVE THAT A LARGE NUMBER OF FLT INSTS WERE IN IMMINENT DANGER OF FAILURE. I DIRECTED THE FE TO RESET THE EQUIP COOLING FAN CIRCUIT BREAKER TO RESTORE COOLING AIR TO THE FLT INSTRUMENTATION ELECTRONICS BAY. IT HELD UNTIL SHORTLY AFTER TOUCHDOWN WHEN IT POPPED AGAIN. DURING THIS SEQUENCE OF EVENTS, I DIRECTED THE FE TO CHK THE HYD SYS AND ANTI-SKID TO ENSURE THAT WE HAD ADEQUATE HYD AND BRAKING SYS TO SUCCESSFULLY COMPLETE THE LNDG. THE LNDG WAS UNEVENTFUL. WE TURNED OFF THE RWY AND PROCEEDED TO THE GATE. ENRTE TO THE GATE, WE TURNED OFF ALL PWR TO THE FLT INSTS IN ORDER TO KEEP THE EQUIP FROM OVERHEATING BECAUSE THE EQUIP COOLING FAN CIRCUIT BREAKER HAD POPPED ON LNDG ROLLOUT. PRIOR TO ENG SHUTDOWN AT GATE ARR, WE NOTED THAT ALL OF THE GENERATORS WERE STILL PWRING THEIR RESPECTIVE BUSSES AND ESSENTIAL PWR WAS OPERATING NORMALLY. MAINT SPECIALISTS MET US TO DISCUSS THE PROBS AND SUBSEQUENTLY TOOK THE ACFT OUT OF SVC FOR FURTHER INSPECTION AND INVESTIGATION. AFTER FURTHER INVESTIGATION AT THE GATE, WE NOTED THAT ALL OF THE EQUIP THAT WE HAD LOST WAS HIGH LOAD AND, FOR THE MOST PART, MOTOR DRIVEN. THERE WERE SEVERAL FAILURES ASSOCIATED WITH CABIN LIGHTING AND LNDG LIGHT CIRCUIT BREAKERS. MOST OF THESE FAILURES WERE ASSOCIATED WITH THE #3 GENERATOR BUSS. IN SPITE OF THE SEEMING GRAVITY OF THESE FAILURES, THE ELECTRICAL SYS PERFORMED EXACTLY AS I EXPECTED AND CONTINUED TO PWR THE ACFT ELECTRICAL BUSSES. THE LOAD SHEDDING WE WITNESSED IS CONSISTENT WITH THE DESIGN OF THIS VERY COMPLICATED SYS. THE WELFARE AND SAFETY OF THIS ACFT AND OCCUPANTS WERE MY UPPERMOST CONCERN THROUGHOUT THIS SEQUENCE OF EVENTS. IN THE HEAT OF THE OP CLOSE TO THE GND, THE CAPT AND CREW WERE FACED WITH APPLYING ALL OF THEIR TRAINING, UTILIZING ALL AVAILABLE ASSISTANCE (IE, EMER PROC CHKLISTS), FLYING THE AIRPLANE AND SUCCESSFULLY LNDG WITH A FAILING ELECTRICAL SYS. WHAT WE LEARNED FROM THIS EVENT IS THAT RUNNING THE EMER PROCS CHKLISTS MAY NOT BE A CLASSICAL SIT WHERE ONE HAS PLENTY OF TIME FOR ANALYSIS AND APPLICATION OF CURATIVE MEASURES. THAT IS WHY WE 'TRAIN, TRAIN, TRAIN' TO INSTILL ABSOLUTE KNOWLEDGE OF EACH ACFT SYS. ONE SMALL MISTAKE IN THIS SEQUENCE OF EVENTS COULD HAVE PRODUCED A SERIOUS SIT CAPABLE OF THREATENING THE SAFETY OF CREW AND PAX. THE SAFETY INVESTIGATION IS STILL INCOMPLETE AS OF THIS WRITING. FURTHER DETAILS REGARDING EQUIP MALFUNCTIONS THAT CAUSED THESE FAILURES WILL BE REVEALED IN AN INTERNAL INVESTIGATIVE PROCESS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT WAS HIGHLY EXPERIENCED IN THE ACFT AND IS AN IOE AND LINE CHK AIRMAN WITH HIS ACR. AFTER LNDG THE ACFT WAS REMOVED FROM SVC. THE ACFT WAS THEN FERRIED TO THE ACR'S MAIN ENGINEERING AND MAINT BASE FOR EXTENSIVE ENGINEERING ANALYSIS. THE FOLLOWING WAS FOUND: 1) THE #3 GENERATOR LOST ONE OF THE AC PHASES. THIS CAUSED ALL HIGH LOAD ITEMS ON #3 BUS TO BEGIN RANDOM POPPING THEIR CIRCUIT BREAKERS. 2) THIS CAUSED GENERATORS #1 AND #2 TO BE REMOVED FROM THE TIE BUS. 3) THE PHASE IMBALANCE WAS CAUSED BY THE DEAD PHASE ON #3 GENERATOR. BOEING'S LONG-TIME SUPPLIER OF BUS TIE BREAKERS IS NO LONGER MANUFACTURING NEW UNITS. A NEW VENDOR HAS STARTED PROVIDING NEW UNITS. AFTER THE INCIDENT, TESTING BY BOEING REVEALED THAT THE BREAKERS MANUFACTURED BY THE NEW VENDOR DO NOT MEET BOEING SPECS. ALL NEWLY MANUFACTURED BREAKERS IN THE INCIDENT ACFT WERE EXAMINED. ALL WERE FOUND TO HAVE PITTED CONTACTS AND SHOWED SIGNS OF OVERHEATING. ONE HAD SIGNS OF A SMALL INTERNAL FIRE. ALL NEW VENDOR GENERATOR CTL AND BUS TIE BREAKERS WERE REPLACED AND NO FURTHER ACFT PROBS HAVE BEEN RPTED. AS PARTS BECOME AVAILABLE, THE ACR IS REPLACING ALL OF THE SUSPECT BREAKERS ON ITS B727 FLEET.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.