Incident Overview
On January 25, 2008, about 0945, United Airlines flight 731, an Airbus A320 registered N462UA, departed runway 22R at Newark Liberty International Airport (EWR), New Jersey. Shortly after takeoff, three of six electronic flight displays went blank: the captain's primary flight display (PFD) and navigational display (ND), along with the upper electronic centralized aircraft monitoring (ECAM) display. The first officer's ND remained functional, and the lower ECAM display also worked, but the first officer reported that the attitude information on his PFD was initially not usable (though it appeared reliable later).
Aircraft Systems Affected
The landing gear did not retract after the handle was moved to the retract position. All radios became inoperative, and the overhead panel was blank. The crew reported that the transponder, traffic alert and collision avoidance system, and standby attitude indicator also failed. The standby attitude indicator, designed to function for about 5 minutes after power loss, stopped working while the aircraft was on the downwind leg of the approach.
Crew Actions
The pilots leveled the aircraft at 2,500 feet, the first assigned altitude, and decided to return to EWR. They landed without further incident; no injuries were reported. After landing, the crew noticed that the "AC ESS FEED" pushbutton on the overhead panel had an illuminated fault indication for the AC 1 electrical bus, which they stated was not illuminated during flight. They manually selected the AC essential bus feed to "alternate," reconfiguring the power supply, after which the captain's instruments and most failed systems resumed functioning.
Personnel and Aircraft Information
The captain, aged 54, held an airline transport pilot certificate with an Airbus A320 type rating and a first-class medical certificate with no limitations. He had approximately 14,500 total flight hours, including about 4,950 in the A320. The first officer, aged 40, held an airline transport pilot certificate with an A320 type rating (second in command) and a first-class medical certificate with no limitations. He had about 5,000 total hours, with approximately 2,290 in the A320.
The A320 flight instruments include captain and first officer PFDs and NDs, and upper and lower ECAM displays. The AC 1 electrical bus normally powers the AC essential bus, DC essential bus, and DC 1 bus. Alternate configuration via the AC 2 bus is manual.
Tests and Research
Maintenance examined the #1 integrated drive generator (IDG) pylon connector and feeder cables, finding no defects. The IDG, bus tie contactor (BTC), and generator control unit (GCU) were removed for testing. The IDG and GCU were tested at Hamilton Sundstrand under representative loading conditions; both passed with no faults. The IDG also passed a production acceptance test and partial disassembly revealed no problems. The BTC passed tests per OEM procedures and showed no defects after partial disassembly.
Previous Incidents
A similar event occurred on October 22, 2005, with a British Airways A319 leaving London Heathrow, where five of six displays went blank. The crew restored power by selecting the AC essential bus feed to alternate. The UK AAIB investigated; no definitive cause for the AC 1 bus fault was determined. As of May 2007, Airbus reported 49 similar events worldwide, with about 37 involving AC 1 bus failures.
Safety Actions
Airbus issued Service Bulletin SB A320-24-1120 (May 31, 2007) for automatic reconfiguration of the AC essential bus, and SB A320-33-1057 (May 11, 2007) to modify standby horizon power supply. The NTSB issued safety recommendations on July 22, 2008, which were subsequently closed. The FAA issued Airworthiness Directives 2009-01-04 and 2010-10-08, and SAFO 08020. EASA issued Airworthiness Directive 2009-0235.