FRANCES FIORINO/NEW YORK

The Transportation Safety Board of Canada is assessing safety benefits of independent standby systems on MD-11s that would serve as a "get-home package" in the event of aircraft electrical failure.

Pilots transitioning to standby systems in adverse circumstances could be "significantly hampered" if those instruments are not in standard layout, according to the Transportation Safety Board advisory.

The move comes out of the safety board's ongoing probe of Swissair Flight 111, an MD-11 that crashed Sept. 2, 1998, near Peggy's Cove, Nova Scotia. The aircraft experienced an inflight fire while en route from New York JFK to Geneva.

In recent weeks, investigators sent a Safety Advisory letter to parties of the probe outlining potential safety problems posed by the layout of standby instrumentation and inadequacies of crew training on those systems.

The advisory asks parties to consider a review of the current Canadian and U.S. Federal Aviation Regulations that cover requirements for standby instrumentation as well as training regulations and practices to ensure crews obtain adequate skills in the use of standby systems.

THE CANADIAN SAFETY Board describes how operation of standby systems might have added to the substantial workload of the Flight 111 crew struggling to handle a dire emergency. Shortly after the flight crew reported smoke in the cockpit, they had to deal with diversion--at night--to an unfamiliar airport, Halifax International.

While the crew was wearing oxygen masks and smoke was permeating the cockpit, the autopilot disengaged and other systems-related failures occurred, some which affected primary instrument displays. The advisory states that there were indications that standby instruments were in use. Shortly after the crew declared an emergency, ATC lost communication with Flight 111, and the MD-11's transponder ceased functioning.

When required, under both CAR 605.41 and FAR 121.305, an aircraft standby attitude indicator must be plainly visible to and usable by any pilot from his station. The advisory states that pilots must be able to quickly adjust the instrument cross-check "T" scan when switching to standby systems. "In adverse circumstances [the transition] could be significantly hampered" by having the instruments positioned away from the normal line of vision and by not having them in standard layout. This could lead to disorientation of the crew and loss of aircraft control.

In the accident aircraft, the magnetic compass, or alternate direction of flight instrumentation, was positioned in a standard location for transport aircraft--at the top of the windshield on the left side of the center post. However, its position in relation to the standby instruments for attitude, altitude and airspeed--located just above the center pedestal--might have added to the crew's difficulties.

The layout would have required a pilot to scan a "considerable" vertical distance, meaning the use of up-and-down head movements, to complete a cross-check--which in turn would increase the chances of disorientation, according to the advisory. The letter adds that the challenge of using standby instruments is greater for crews who either are not well trained or have not had recent practice in their use.

Regulations also state the standby attitude indicator (AI) must be powered from a source independent of the electrical generating system. In the accident aircraft, the AI is powered from battery bus, which is independent. There is no requirement, however, for standby instruments to remain powered by an independent power supply separate from the aircraft electrical system and battery, according to the advisory.

THE ADVISORY STATES Swissair modified the standby flight instrument equipment in its aircraft following the crash of Flight 111. The carrier installed a secondary flight display system (SFDS) on its MD-11s that is similar in layout to the primary flight display. The SFDS has an auxiliary battery to supply power for a minimum of 45 min.

The parties to the investigation may voluntarily fulfill the safety board's requests to review regulatory requirements outlined in the advisory. If investigators discover other evidence that may require further action, the board would issue a safety recommendation.

 

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©April 14, 2003, The McGraw-Hill Companies Inc.