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Difficult to see

Wed, Jan 30, 2008 — David Evans

Briefs

The pilots heard a “clunk,” then the flight deck became very dark as the British Airways (BA) A319 was approaching 20,000 feet during climb after departure from London’s Heathrow Airport in October 2005 with 82 passengers and crew aboard. Most of the affected systems were restored in about 90 seconds, when the crew switched the AC Essential Feed to alternate (“ALTN”). The UK Air Accidents Investigation Branch (AAIB) just recently issued its report of investigation into what was described as a “serious incident.”

The AAIB said, “It was not possible to determine the cause of the incident due to a lack of evidence.” When electrical power was restored, and after radio consultation with the airline, the aircraft continued to its Budapest destination. The duration of the flight was such that the 30-minute cockpit voice recorder (CVR) was overwritten, and the non-BA technician at Budapest did not investigate the incident, although it was reported verbally by the captain. The technical log reflected “minor defects” and the faxed copy of the air safety report (ASR) was not received by BA’s flight operations safety department or the department responsible for entering the incident on the electronic safety management database. This meant the significance of the incident was not fully appreciated until the original copy of the ASR arrived at BA’s Heathrow offices by mail. Moreover, as the AAIB admitted, the flight data recorder would have been unable to capture the detailed information of the failure anyway (i.e., insufficient parameters). A cockpit camera would probably have captured more useful data.

The AAIB report said there was a “major” electrical failure:

“This resulted in the loss or degradation of a number of important aircraft systems. The crew reported that both the commander’s and co-pilot’s Primary Flight Displays (PFD) and Navigation Displays (ND) went blank, as did the upper ECAM [Electronic Centralized Aircraft Monitoring] display. The autopilot and autothrust systems disconnected, the VHF radio and intercom were inoperative and most of the cockpit lighting went off.”

The cabin lights also went out momentarily. In other words, the electrical failure pitched the aircraft into a deep, dark and blind position.

“This and other similar incidents show that there is at least one unforeseen failure mode on A320 family aircraft which can cause the simultaneous loss of the captain’s and co-pilot’s electronic flight instruments and the upper ECAM display,” the AAIB intoned.

The captain used the luckily visible night horizon for reference. If the A319 primary displays are unavailable, the A319 can be flown on standby instruments, which include a horizon, altimeter, airspeed indicator and compass. But these standby instruments were “difficult to see in poor light,” the AAIB says (see Figure A). One should expect such instruments to be needed all the more in poor light conditions, and independent illumination and more prominent positioning on the instrument panel should be requisite (see Figure B).

Figure A
Image
As it stands in the A319, the standby artificial horizon, shown here located in the center of the panel, is distant from the primary flight displays, making comparisons between the two problematic – not to mention that the alternate instruments are difficult to see when lighting fails. This location, as in out of sight/out of mind, would be of little help in resolving an instantaneously developing unusual attitude or loss of attitude control situation. It would also be very difficult to fly off of in the electrical failure situation addressed by the AAIB incident report.
Figure B
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A suggested relocation of the standby artificial horizon on the glareshield, for both the captain and the first officer, providing ready comparison to the primary flight display and keeping the same relative instrument scan when only the standby instruments are available. Logic and normal instrument scanning techniques would require the standby radiomagnetic indicator to be close to the standby artificial horizon. There is no dearth of instrument panel real estate.

Perhaps worse, according to the AAIB, “The flight crew had not received any formal training on how to operate A320 family aircraft by sole reference to standby instruments.” It should be noted that such training is not a part of the new Multi-Crew Pilot License (MPL) training syllabus.

Those instruments, difficult to see as they may be, are there precisely for situations like this. The absence of formal training in their use seems a major shortcoming, despite this crew’s excellent handling of the situation.

Of greater consequence is the admission that, had the aircraft been equipped with the optional mechanical version of standby instruments, these would have been unavailable in the circumstances of this electrical failure. The prospect of a modern airliner being stuck in clouds at night without any attitude reference whatsoever is exceedingly dangerous – and likely instantly catastrophic. The AAIB said:

“The unexplained simultaneous malfunctions of the commander’s and co-pilot’s primary flight instruments has significant implications for those aircraft with a pre-ISIS wiring configuration for the standby instruments. If this incident had occurred o one of these aircraft, the standby horizon would no longer have been powered and would have become unusable after approximately five minutes, leaving the crew without any instrumented attitude reference. This would preclude their ability to maintain control of the aircraft in conditions where there is no visible external horizon.” (For the full AAIB report, see http://tinyurl.com/34vq7c)


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