SYNOPSIS

2/15/99

WHILE EN ROUTE TO YIP FROM IND, THE FLIGHT ENGINEER FOUND THE NR 1 ENGINE FIRE DETECTION CIRCUIT BREAKER HAD TRIPPED.  ATTEMPTED ONE RESET, BUT THE CIRCUIT BREAKER WOULD NOT RESET.  THERE WAS A BURNING RUBBER SMELL NOTED IN THE COCKPIT.  DECLARED AN EMERGENCY INTO YIP.  THE PLANE LANDED WITHOUT FURTHER INCIDENT.  MAINTENANCE TRACED THE BURNING SMELL BACK TO THE CIRCUIT BREAKER.  THE CIRCUIT BREAKER WAS REPLACED AND A OPERATIONAL TEST OF THE SYSTEM WAS CARRIED OUT OK.  THE AIR CRAFT WAS THEN RETURNED TO SERVICE.  (M) 

4/28/99

IAH - FLT 612 - IMMEDIATELY AFTER TAKEOFF NOTICED ELECTRICAL SMELL IN COCKPIT.  SMELL WENT AWAY IN A FEW MINUTES.  DURING CLIMB-OUT NOTICED LEFT IGNITION C/B TRIPPED.  RESET C/B PER QRH, WOULD NOT RESET.  GOT A BEEP NOISE AND SPARKS CAME OUT OF OVERHEAD PANEL NEAR IGNITION SWITCH.  REPLACED IGNITION SWITCH.  OPS CHECK NORMAL.  (M)   

6/9/99

WHILE EN ROUTE, THE EMERGENCY CABIN LIGHTS ILLUMINATED EMERGENCY LIGHTS ARM AND CHARGE CIRCUIT BREAKER WAS POPPED BUT DI D RESET.  REPAIRED CHAFFED WIRE ABOVE RIGHT LAV.    

6/19/99

MID AND AFT CARGO C/B'S POPPED AND WOULD NOT RESET.  ALSO, THE ORD LIGHTS C/B AT 3C11.  THIS HAPPENED WHEN STARTING TO C LOSE CARGO DOOR FOR DEPT BOS.  MTC IN PROGRESS TO REPAIR BURNT WIRING TO 2 WIRE BUNDLES IN MESC LT O/B CEILING AREA BUND LE M911 AND M915.   

WHILE CHECKING INOPERATIVE VIDEO ENTERTAINMENT SYSTEM PROBLEM, FOUND BUFFER BOX NR 2 AND NR 3 CIRCUIT BREAKERS POPPED. ATTEMPTED RESET RESULTED IN SPARKS IN VIDEO CLOSET BEHIND VIDEO EQUIPMENT.  SUBSEQUENT INVESTIGATION UNCOVERED BURNED WIRES AT CONNECTOR P3-D9030, P3-D9032 AND  P3-D9031.   

10/9/99

ORD - FLT 1817 - EN ROUTE FROM PHL/MSP, CAPTAIN REPORTED THE NR 2  AND NR 3 TRANSFORMER RECTIFIERS HAD TRIPPED AND THE CAPTAIN'S WINDOW OVERHEAT LIGHT WAS ON.  CAPTAIN RESET T/R'S, BUT THEY BOTH TRIPPED AGAIN.  LOSS OF ELECTRIC TRIM, AUTOSPEED BRAKE AND RIGHT GENERATOR WAS NOTED.  AN ELECTRICAL SMELL IN THE COCKPIT WAS ALSO NOTED.  FLIGHT DIVERTED TO ORD AND LANDED WITHOUT FURTHER INCIDENT.  NO EMERGENCY WAS DECLARED.  MAINTENANCE REMOVED AND REPLACED THE NR 2 ENGINE GENERATOR FEEDER HARNESS.  RAN ENGINE.  OPERATIONAL CHECK NORMAL.  (X) 

                                                                                               

     Air Line Pilots Association  International

 

                                                                                                                                          February 18, 2000

Mr. Tom McSweeny    

Director of Regulation and Certification

FAA

800 Independence Ave

Washington D.C.

 

Dear Mr. McSweeny:

At a recent ATSRAC meeting there was considerable discussion about resetting tripped circuit breakers. Members expressed concern about malfunctioning electrical circuits as a source of ignition for an aircraft fire. The Air Line Pilots Association (ALPA) volunteered to address the concerns outside of ATSRAC by developing suggested language for an FAA policy letter on resetting tripped circuit breakers. This specifically excluded any procedures developed to pull and reset circuit breakers for troubleshooting purposes. The recommended language below is a coordinated product of AECMA, Airbus Industrie, ALPA, ATA, and the Boeing Company.  Each party had the opportunity to review the ALPA draft language and provide comments that we will be happy to provide at your request. We have tried to address and incorporate the input from all participants.

 

Current circuit breaker reset policies were developed independently by individual operators and manufacturers. This led to a wide variance on how to handle a tripped circuit breaker.  Most pilots are taught that the "proper" way to reset a circuit breaker is to allow a cooling period, generally 1-3 minutes, then reset the breaker.  In fact, tripped circuit breakers have come to be viewed by pilots as a relatively benign, if not common, occurrence.  Most pilots have experienced resetting a tripped circuit breaker with no adverse results. This then reinforced the belief that resetting circuit breakers, even multiple times, is a safe procedure.  However, a review of just a few Service Difficulty Reports involving tripped and reset circuit breakers (attachment 1) demonstrates that this is not always the case.  It is therefore imperative that any policy statement emphasize the potential hazard represented by resetting a tripped circuit breaker.

 

A review of the available guidance (attachment 2) suggests that the industry recognizes the potential significant hazard associated with resetting circuit breakers, particularly if the cause of the trip is not known. The FAA guidance suggests that the type of wiring involved may bear directly on a pilot's decision to reset a tripped circuit breaker. If the circuit contains polyimide wiring insulation, resetting a tripped circuit breaker can have serious consequences.  However, the flight crew responding to a tripped circuit breaker generally has no way of knowing if this type of wire is in use on the affected circuit.


At least one major manufacturer has recently established a policy of no inflight circuit breaker resets. Their general feeling was that there was no single component that was critical enough to justify the risk of resetting a tripped circuit breaker. Since these discussions have taken place they have refined their policy even more. Their new policies almost mirror the suggested language below. Another manufacturer allows one reset, unless a fuel pump is involved, in which case reset is prohibited. 

 

The discussions and correspondence that resulted from our initial proposed language for the policy resulted in a very healthy “airing out” of the issue. The industry group that participated in drafting the recommendation was in general agreement that any FAA policy on resetting tripped circuit breakers should highlight potential hazards and make clear that resetting a tripped circuit breaker has definite risks.  Clearly, no policy can anticipate every situation, so the pilot in command must retain the authority to make a final decision based on the available facts. We therefore recommend the following language be adopted as the FAA policy on resetting tripped circuit breakers.  

 

"There is an inherent danger in resetting a tripped circuit breaker. A tripped circuit breaker is a signal that something is probably wrong in the circuit. Until it is ascertained what has caused the trip to take place, the crew has no way of knowing the hazards of resetting the circuit breaker. The ignition of a fire is a real possibility. Therefore, a tripped circuit breaker should not be reset in flight, unless, in the judgment of the Captain, it is necessary for the safe completion of the flight. Ground resets should only be accomplished after maintenance has ascertained the reason for the trip and there is no danger. After any tripped circuit breaker reset maintenance personnel shall insure the malfunction and subsequent resetting does not result in a hazard to safe flight.”

In addition, we believe that whenever a circuit breaker trips that it should require a mandatory logbook write-up that includes the conditions when the trip occurred. We recognize that many circuit breaker trips cannot be duplicated by maintenance personnel. If it is required to report all circuit breaker trips, then it will establish a history under what conditions those CND (Can Not Duplicate) trips occur and will aid maintenance personnel in their troubleshooting procedures.

 

Thank you for the opportunity to participate in the development of this policy.

 

 

                                                                        Sincerely,

 

                                                                        Captain Paul McCarthy

                                                                        Executive Air Safety Chairman

                                                                        Air Line Pilots Association


Data Extracted from 1999 Service Difficulty Reports

DATE

2/24/99

CIRCUIT BREAKER L20 POPPED, SMOKE ODOR PRESENT ON RESET.  MAINTENANCE REPLACED CONVERTER 12LL, OPS CHECK GOOD.   

 

5/22/99

JAX - FLT 1023 - EN ROUTE FROM PHL TO MIA, CREW REPORTED THE RIGHT PACK TEMPERATURE INDICATION READ 200 DEGREES ALL THE TIME.  CREW ALSO REPORTED THE UPPER ANTI-COLLISION BEACON CIRCUIT BREAKER WAS FOUND OPEN AND WHEN AN ATTEMPT TO RESET THE BREAKER WAS ACCOMPLISHED, THE BREAKER RE-OPENED CAUSING SMOKE TO APPEAR IN THE PASSENGER MID-CABIN.  FLIGHT DIVERTED T O JAX AND LANDED WITHOUT FURTHER INCIDENT.  MAINTENANCE REMOVED AND REPLACED THE RIGHT PACK TEMPERATURE BULB (P/N MS5280 34-1).  OPERATIONAL CHECK OF RIGHT PACK NORMAL.  MAINTENANCE DETERMINED THE SMOKE TO COME FROM A FAILED UPPER ANTI-COLLISION BEACON.  OPERATIONAL CHECK NORMAL.  (X)

 

6/12/99

FOUND C/B FOR 2R DOOR ELECTRIC MOTOR POPPED, WOULD NOT RESET.  FWD TO MCO AND PLACARD.     

 

6/28/99

PILOT NOTED THE RIGHT LANDING LIGHT CIRCUIT BREAKER TRIPPED.  PILOT RESET BREAKER AND IT TRIPPED AGAIN.  INVESTIGATION REVEALED THE RIGHT MAIN FUEL TRANSFER PUMP WAS SHORTING THIS CIRCUIT.  (NOTE:  BOTH THE LANDING LIGHT AND TRANSFER PUMP A RE ON THE SAME CIRCUIT).  THIS PUMP SHOWS SIGNS OF ARCING AND BURN MARKS AT THE POINT THE SHIELDED POWER WIRE ENTERS THE PUMP.  

 

9/25/99

10/4/99

INSTRUMENT LIGHTS FAILED.  TWO MINUTES LATER, THE INSTRUMENT LIGHTS CIRCUIT BREAKER TRIPPED.  PILOT RESET THE CIRCUIT BREAKER.  APPROXIMATELY FOUR MINUTES LATER, THE SMELL OF SMOKE WAS OBSERVED.  AIRCRAFT WAS ON FINAL APPROACH AT THIS TIME AND SAFE LANDING WAS ACCOMPLISHED.  NO EVIDENCE OF FLAME INSIDE OR AROUND LIGHT CONTROL UNIT.  APPARENT INTERNAL SHORT O F CIRCUIT BOARD CAUSED ODOR OF BURNING WIRES AND SMOKE.  

 

11/2/99

LEFT COFFEEMAKER POPPED.  RESETTING CENTER C/B CAUSES ARCING IN AFT COFFEEMAKER.  ISOLATED PROBLEM TO NR 2 C/M IN LEFT A FT GALLEY.  PULLED AND COLLARED POWER C/B FOR NR 2 C/M.  FWD TO MCO AND PLACARD.  C/M NASI LGW.    

 

Selected FAA and Industry Guidance on Resetting Tripped Circuit Breakers

 

From FAA Advisory Circular 25-16 

6 a (4) (viii): “… service experience of aromatic polyimide insulation, as presently constructed, documents a failure mode called “insulation flashover” where conduction at insulation breakdown areas has damaged or destroyed the wire or wire bundle in which it occurs… Arcing on wire insulation, or  “arc tracking,” can result from electrolytic contamination of wire having insulation cracks or cuts that expose the conductor. It can also result from chafing damage that reduces the dielectric strength of dry insulation. Each successive attempt to restore an automatically disconnected power source, or the resetting of an automatically disconnected CPD [circuit protection device], can result in progressively worse effects ...” 

7 g. "Information should be provided in FAA approved AFMs … that the crew should make only one attempt to restore an automatically disconnected power source or reset or replace an automatically disconnected CPD that affects flight operations or safety."

7 h. Some electrical faults or failure modes can result in the automatic disconnection of a power source, bus, or high current load for which power cannot be restored … without maintenance action. Such a disconnection could result in a serious latent failure of a flight control system component if the fault or failure mode occurs in its vicinity. For this reason, it is important that maintenance personnel determine by close inspection of related and nonrelated components in the vicinity of the fault, and before the next flight, that such a latent failure has not occurred." 

 

From the ATA Standard Wiring Practices Manual; Safety Practices, Circuit Breaker Reset:

"...when a circuit breaker trips or opens, do not attempt to reset or close the breaker until the … malfunction that caused the breaker to trip … has been determined and corrected".

 

From the Airbus Flight Crew Operating Manual for the A300/310/319/320/321:

“In flight, the flight crew must not reengage a tripped C/B. On the ground if the pilot coordinates the action with maintenance he may reengage a tripped C/B provided the cause of the tripped C/B is identified.”

From a planned change to the Airbus FCOM:

"… the likely cause for circuit breaker tripping is an abnormality in the electrical load or in the associated wiring.  Consequently, the reengagement of a tripped circuit breaker may aggravate the electrical damage by propagating the electrical damage with possible risk of affecting other equipment supplied by the affected busbar or may even result in a temperature increase in the area where the defect occurred…Airbus Industrie do not authorize a pilot to reengage a circuit breaker having tripped by itself, unless the captain, using his/her emergency authority, judges it necessary for a safe continuation of the flight. In this last case, only one re‑engagement should be attempted…FCOM vol 3, abnormal procedure 3.02.24 p24 "c/b tripped" has been revised to highlight that the flight crew must not reengage a tripped c/b in flight and must coordinate with maintenance for reengagement on ground."

 

From Boeing:

“Resetting circuit breakers is not generally a requirement in flight. However, a tripped circuit breaker (other than a fuel pump C/B) may be reset at the Captain’s discretion, after a short cooling period (approximately 2 minutes). If it trips again no further attempt is to be made to reset that C/B.”

SUCCESS (an FAA POLICY - Aug 00)

ALPA’s Paul McCarthy’s Congressional Testimony  ALPA on Aircraft Wiring       ALPA Supports Aging Aircraft Wiring Research

 

 

ALPA on Aging Wire (Capt Ken Adams)                 ALPA’s Virgin Bus               ALPA Supports Fire Precautions

 

 

The Risk of Resetting CB's                                       ALPA- A New Approach to Cockpit & Cabin Fire Safety (Capt Ken Adams)

         (Air Safety Week Magazine Story)

 

Safety Problems With Electrical Systems                   Swissair Flight 111             Wiring Woes Can Be Predicted
        on Geriatric Airliners                                   

 

                            

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