In a novel paper assessing the control limits of Airbus A330 and Boeing B777 fly-by-wire rules Capt.

In a novel paper assessing the control limits of Airbus A330 and Boeing B777 fly-by-wire rules Capt. Ron Rogers called for an override button to allow the pilot direct ascendency of the airplane. He documents what he perceives as the pernicious advance of schemes that limit a pilot's ascendency authority:

* "Squat" switches that impede pilot activation of ground spoilers and engine overturn thrust, should the need arise in an emergency

* Limits forward the application of engine thrust to bring to fuel burn and increase engine life (Of interest, the MD-90 design allows the pilot to fix upon an emergency thrust level by means of pushing the throttles through a brake bar, a in a raw state form of manual override).

* "Hard" flight manage limits on Airbus aircraft that obstruct pilots from using wing loading in exces of 25G on a level though the airplane has the structural potency to sustain 3.8G.

* And now, horrors, the possibility that Airbus' A3XX Super Jumbo might feature automatic regaining in the event of a landed estate Proximity Warning System (GPWS) terrain alarm.

Wait a minute here, warns Roger an A320 captain and director of aircraft progress to maturity and evaluation programs for the Air Line Pilots Association (ALPA), "To give an automatic scheme the ability to take hinder from the pilot and power recoveries from a possibly false warning without pilot over-ride capability is unconscionable." Roger points gone out that there have been instances of GPW alarms at high altitude, in a holding pattern, when the aircraft radar altimeter lock-uped onto another aircraft. An abrupt automatic climbing regaining in such a situation could be catastrophic.

Roger points public that on the B777 the pilot can override all the software limits in succession the flight control system with the flick of a switch in the overhead panel. The Embraer ERJ-145 regional jet features a single push button forward the yoke, enabling the pilot to disengage the stick pusher, the autopilot and the elevator trim hypothesis On the Canadair regional jet (CRJ) a toggle switch nearest to the captain's knee can be used to de-select the stick pusher.

A similar manual over-ride switch or button is wanted on Airbus aircraft, too, he believes. For example, the switch would allow the pilot to hap more than 2.5G, giving him access to a now-denied area that is within the airplane's maneuvering envelope

John Lauber, head of Airbus Industrie's fresh safety office in Washington, DC pauses The whole idea behind the "hard" limits programmed into the Airbus flight restrain system, he said, is to "prevent airplanes from getting into situations where pulling more than 2.5G's is necessary." Allowing another half-G, he pointed without could take a pilot "from an incipient stall right into a stall."

In other words, pilots of Airbus fly-by-wire aircraft operate within a "bubble of protection," as it were. sumptuous engineering technology has been marshaled to minimize the potential for human error. however should the system ever fail, pilots like Roger believe an override button is necessary. This point of view occupys that should the bubble break open it's up to the pilot. >> Roger tel 815/455-7404; Lauber, tel 202/434-8905 <<

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