Pb électriques famille A320

Airbus A319 suffered previous electrical woes
By: Malcolm Payne

October 1, 2009
Accidents


On a Sept. 15, 2006 flight from Alicante, Spain, to Bristol, England, the captain of an Airbus A319 lost all his displays, auto-pilot and autothrust over Nantes, France. He handed control over to the copilot, who had all his displays, except the flight director, and would need to hand-fly using raw data. The commander tried to make contact with Brest Control using all radio facilities, but with no success. Attempts to reconfigure the electrical power supply were not successful.

At Brest Control all traces from of the Airbus had vanished from the radar controllers’ screens. Flight AAL63, which was a potential conflict, was instructed to descend and soon afterwards the crew reported seeing an “Easyjet 737” pass overhead northbound, although it was not displaying on AAL63’s TCAS.

Ten minutes after the incident the captain gave up trying to contact Brest and selected the emergency code on the number-two transponder. Shortly thereafter, the secondary radar trace for the Airbus reappeared on the radar controller’s display and one minute later the code changed to 7700. The airplane continued to Bristol and landed without incident, although on arrival at the parking area it was necessary to use the fire switches to shut down.

In-flight Power Troubles

The previous day, on a flight from London Stansted to Alicante, Spain, with a different crew, the airplane suffered a failure of the left generator control unit. The crew was unable to reset the system, so the pilots isolated the generator and started the APU to supply the left system. After arrival at Alicante, an engineer was unable to fix the defect but, in accordance with the company minimum equipment list, the aircraft was cleared to fly the next sector to Bristol, England, using the APU in place of the generator.

The airplane had a history of electrical-power supply problems in the eight weeks before the incident, but the maintenance department considered it unexceptional.

The UK Air Accidents Investigation Branch (AAIB) could not identify why the crew was unable to reconfigure the power supply system. However, it determined that the design of the aircraft electrical system–which required the crew to manually reconfigure the electrical feed to the essential AC system–was a contributing factor. Investigators also criticized the master minimum equip- ment list that allowed an aircraft to be dispatched without taking into account its previous electrical system history.

A further factor stemmed from inadequate record keeping at Hamilton Sundstrand, makers of the generator control unit. This unit had been returned to them three times in the previous five months. On each occasion it was returned to service as no fault found. Intermittency is the most difficult fault to pinpoint, but investigators determined that a better record of unit numbers and cross-referencing would have alerted the overhaul department to a service history.

The AAIB is aware of three similar electrical system failures in the A320 series. These are G-EUOB, October 2005 (AIN, January 2006); G-OZBE, 23 April 2007; and a U.S.-registered A320, currently under investigation by the NTSB.

Airbus faces demands for A320 series electrical systems improvement following EasyJet report
By David Learmount

The final report on a serious in-flight electrical system failure in an Airbus A319 contains 14 recommendations for changes to equipment, engineering procedure and operational security,

En route from Alicante, Spain to Bristol, UK on 15 September 2006, the EasyJet aircraft (G-EZAC) suffered a loss of electrical power that left the captain with no flight instruments, and the aircraft with no autopilot or autothrottle and no means of communication for the remainder of the flight, according to the UK Air Accidents Investigation Branch report.

In addition, the loss of all transponder signals from G-EZAC for about 10min over north-west France deprived Brest air traffic control of its ability to track the aircraft, at the same time as rendering traffic alert and collision avoidance systems ineffective.


The captain elected to continue the flight to its destination because he had good weather reports for Bristol and feared that divergence from the planned route with no communication might precipitate interception by military aircraft with potentially serious consequences because, with curtailed aircraft capabilities, he might not be able to comply with intercept signals.

The AAIB report says: "While in the cruise at flight level 320 (32,000ft/9,750m) in visual meteorological conditions, the aircraft suffered severe disruption of the electrical power system, causing multiple aircraft systems either to cease operating or to become degraded, significantly increasing the flightcrew's workload. All means of radio communications became inoperative and remained so because they all relied on a single busbar which de-energised and was unavailable for the remainder of the flight."

The causes of the incident, according to the AAIB, included "an intermittent fault in the No 1 generator control unit, which caused the loss of the left electrical network; an aircraft electrical system design which required manual reconfiguration of the electrical feed to the AC Essential busbar in the event of de‑energisation of the No 1 AC busbar, leading to the loss or degradation of multiple aircraft systems, until the electrical system is reconfigured; and the inability of the flightcrew to reconfigure the electrical system, for reasons which could not be established".

The aircraft had been dispatched from Alicante under a minimum equipment list provision despite the No 1 main generator being declared unserviceable on the inbound flight and not repaired. The left electrical system was powered by the auxiliary power unit generator.

The investigator remarked that, in this case, the aircraft was stable in the cruise in VMC conditions but the failure could equally have occurred in instrument meteorological conditions and at low level in a critical phase of flight.

For these and other reasons, says the AAIB, "the potential hazard of loss of the AC BUS 1, AC ESS and DC ESS busbars was more serious than the airworthiness authorities had assessed". The AAIB, after a previous A320 series electrical incident, recommended on 13 December 2006 that Airbus introduce a modification to automate the transfer of the electrical feed to the AC ESS busbar in the event of the loss of the AC BUS 1 busbar.
Airbus issued a service bulletin to enable this in 2007, and the AAIB's G-EZAC report has repeated the call for this change to be implemented.

The European Aviation Safety Agency has told the AAIB it will make this modification compulsory.

Included in additional recommendations are that EASA should require the modification of affected A320‑series aircraft so that the loss of a single busbar does not result in the complete loss of radio telephony communications; EASA should require Airbus to review the A320‑series master minimum equipment list provision that an aircraft may be dispatched with an integrated drive generator inoperative; Hamilton Sundstrand should modify its repair and overhaul procedures to ensure that a unit with an excessive service rejection rate or a recurrent fault is not repeatedly released back to service.

Finally, the AAIB recommends that, because of security concerns, EASA and the US Federal Aviation Administration should formally recategorise incidents involving total communications loss from "serious" to "hazardous".

Airbus is to warning operators of A320 family aircraft about the potential for an electrical fault to cause display failures as well as uncommanded rudder trim movement and control difficulties after an alarming incident involving a BMI A321 in August.

The Airbus A321 was en route over northern Sudan operating a night-flight from Khartoum to Beirut on Aug. 24 when the incident happened.

According to a bulletin issued by the U.K. Air Accidents Investigation Branch (AAIB), an electrical fault led to a series of display and control problems. These included the intermittent failure of both pilots’ electronic displays and the uncommanded application of left rudder trim. The AAIB says that the flight crew also reported that the aircraft did not seem to respond as expected to control inputs and “shuddered and jolted repeatedly”.

It adds that as a result of the uncommanded rudder trim, the Airbus adopted a left-wing-low attitude and deviated left of track. The cockpit lights also switched off and on intermittently. The crew also reported hearing “chattering” from the circuit breaker panels.

During the incident the crew flew the A321 manually, referring to the standby instruments which continued to function normally.

The problem was rectified after the crew switched off the No. 1 generator in response to an ‘ELEC GEN 1 FAULT’ message on the Airbus’s ECAM warning display, says the AAIB.

The cause has been traced to an electrical problem and the AAIB says that Airbus indicates that a reset of the Flight Augmentation Computer, caused by an electrical power interruption, can result in incremental offsets in rudder trim.

The AAIB is continuing to probe the incident with Airbus and France’s BEA investigation agency. In the meantime, Airbus, in response to an AAIB recommendation, is alerting all A320 family operators that an electrical power generation system fault may not be clearly annunciated on the ECAM, and that it may lead to uncommanded rudder trim operation.