Airbus A320United Airlines Inc
Newark, NJ, USA · 2008-01-25·N462UA
What happened
NTSB summary, verbatimThis incident occurred when United Airlines flight 731 experienced a fault in the airplane's AC 1 electrical bus, one of the two primary electrical distribution systems for the airplane, which in turn caused a number of other electrical busses on the aircraft to lose power. The loss of this electrical power led to the loss of a number of aircraft displays and systems. During the flights return to the airport, multiple messages on the electronic centralized aircraft monitoring (ECAM) system, which provides information to the crew regarding failures that have occurred on the aircraft along with recommended corrective actions, were being displayed then removed by the ECAM system, making it difficult for the flight crew to interpret and address the error messages. There were no faults found in the airplane wiring and the testing and teardown found don faults in the #1 integrated drive generator (IDG), bus tie contactor (BTC), and generator control unit (GCU).
Photographs
1the aircraft, and what the investigators foundProbable cause
the Board's determinationa fault in the airplane's AC 1 electrical bus that caused a number of other electrical busses on the aircraft to lose power.
Occurrence sequence
1 stepsNTSB coding · CICTT taxonomy- 1 · Initial climbElectrical system malf/failuredefining event
Findings
1 causal · 0 contributing- CAUSEAircraft › Aircraft systems › Electrical power system › AC power distribution system — Malfunction
Safety recommendations
6 issuedwhat changed because of this accidentTO THE FEDERAL AVIATION ADMINISTRATION: Require all operators of Airbus A320 family aircraft to modify these aircraft in accordance with Airbus Service Bulletin A320-24-1120 to provide the automatic reconfiguration of the AC essential bus power supply in the event that the AC 1 electrical bus fails.
TO THE FEDERAL AVIATION ADMINISTRATION: Require Airbus to develop a modification for in-service A320 family aircraft such that, in the event of an AC 1 electrical bus failure, the standby attitude indicator is powered by an additional power source that will last for a minimum of 30 minutes, and require operators to incorporate this modification as soon as possible after it is available.
TO THE FEDERAL AVIATION ADMINISTRATION: Require all operators of A320 family aircraft to develop new procedures, if necessary, and to provide flight crews with guidance and simulator training regarding the symptoms and resolution procedures for the loss of flight displays and systems in conjunction with an AC 1 electrical bus failure.
TO THE EUROPEAN AVIATION SAFETY AGENCY: Require all operators of Airbus A320 family aircraft to modify these aircraft in accordance with Airbus Service Bulletin A320-24-1120 to provide the automatic reconfiguration of the AC essential bus power supply in the event that the AC 1 electrical bus fails.
TO THE EUROPEAN AVIATION SAFETY AGENCY: Require Airbus to develop a modification for in-service A320 family aircraft such that, in the event of an AC 1 electrical bus failure, the standby attitude indicator is powered by an additional power source that will last for a minimum of 30 minutes, and require operators to incorporate this modification as soon as possible after it is available.
TO THE EUROPEAN AVIATION SAFETY AGENCY: Require all operators of A320 aircraft to develop new procedures, if necessary, and to provide flight crews with guidance and simulator training regarding the symptoms and resolution procedures for the loss of flight displays and systems in conjunction with an AC 1 electrical bus failure.
Sequence of events
5 timed eventsfrom the FDR factual report · claude-fable-5-1 (in-session)- takeofftakeoffp.3Aircraft took off at an indicated airspeed of approximately 170 knots and began to climb
- about 10 seconds after liftoffclimbp.4DC Bus ESS, AC Bus ESS and AC Bus 1 parameters turned from on to off; autopilot parameters began recording non-computed data
- about 2 minutes laterclimbp.4Altitude and airspeed parameters began recording non-computed data
- 13 minutes 15 seconds after takeofflandingp.4Aircraft landed at Newark
- about 7 minutes after landinggroundp.4DC Bus ESS and AC Bus ESS turned on; altitude and autopilot parameters resumed recording valid data
NTSB analysis
from the final reportThis incident occurred when United Airlines flight 731 experienced a fault in the airplane's AC 1 electrical bus, one of the two primary electrical distribution systems for the airplane, which in turn caused a number of other electrical busses on the aircraft to lose power. The loss of this electrical power led to the loss of a number of aircraft displays and systems. During the flights return to the airport, multiple messages on the electronic centralized aircraft monitoring (ECAM) system, which provides information to the crew regarding failures that have occurred on the aircraft along with recommended corrective actions, were being displayed then removed by the ECAM system, making it difficult for the flight crew to interpret and address the error messages. There were no faults found in the airplane wiring and the testing and teardown found don faults in the #1 integrated drive generator (IDG), bus tie contactor (BTC), and generator control unit (GCU).