Lufthansa wing-strike probe queries A320 landing logic

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FlightBot Posted: Fri, Mar 5 2010 9:42 PM

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German investigators believe Airbus should assess aspects of A320 flight logic after determining that partial loss

Author: David Kaminski-Morrow

Date: 05 March 2010

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licekwallion replied on Sat, Mar 6 2010 4:45 AM

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Lee replied on Sat, Mar 6 2010 5:41 PM

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Thanks for the update.

There are also reports that one of the pilots selected the wrong switch as an earlier part of this process, but that does not excuse dangers that have been surfacing because of increased computerization of aircraft flight control systems, some of which may also have contributed to the Air France Flight 447 disaster. The Lufthansa flight on which you so rightly focus is just another in a long series. Take, for example:

• the fatal 1993 Luftnansa landing accident in which the A320's automated landing system kept the pilot from deploying wing spoilers while landing under rainy, gusty conditions at night. Without maximum decleration, the plane burst into flames after overrunning the end of the runway. Airbus subsequently quietly programmed landing gear sensors to permit spoiler deployment at less than half the previous weight threshold. (See telecast of "Fatal Logic," a German investigative documentary that came out the following year.)
• Numerous instances of "uincommanded rudder" suffered by FedEx and, especially, American Airlines with their A300-600Rs (now retired from service)--some severe enough to cause emergency landings. Did another such an uncommanded rudder incident play a role in the crash of AA587 in 2001?
• A 1991 Interflug A310 incident in which a pilot had to struggle with his autopilot for control of the aircraft during a go-around. Disaster was imminent. When he finally regained control and landed, the tail fin was found to have exceeded Ultimate Load.
• Failure of ADIRUs on two separate QANTAS flights in 2008, leading in one case to a sudden dive initiated by the flight control computer--and to injuries to one third of the passengers, some of them severe. (See Mark Thompson's report in TIME.)

The list goes on.

AF 447 black boxes may not (yet) have been found, but the evidence above, and many other such examples, suggest that under the stresses of the storms through which that A330 was flying, any similar glitch in the Airbus's computerized flight control system may have surfaced and started a cascading chain of events that doomed the aircraft. Yet no standdown has been called for Airbus flight control software. After the AA5897 disaster in 2001, Airbus modified its flight control software without telling the NTSB or American Airlines until an American Airlines pilot attending a 2002 NTSB hearing got an Aribus rep to admit that, yes, they had 'adjusted' the software...'for passenger comfort.' At that point, it was obviously too late to evaluate the previous software iteration.

Compounding the problem, of course, is that with more and more short- and long-range flights being flown while under autopilot control, pilots get fewer opportunites to maintain their own basic flying skills in the face of minor upsets and employ the intuitive aerodynamic sense imbued in them during their basic flight school training (or during their previous military careeres). Quick, instictive reflex action is sometimes needed in an emergency--and pilots are increasingly flying with two strikes against them as this problem just begins to surface. Airlines and the relevant national safety organizations need to address this issue with appropriate steps.    

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mcpcshowcaseHD replied on Sun, Mar 7 2010 10:43 AM

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The control surfaces of the A300/A310 are not Fly by Wire controlled. The FBW features were only introduced when the A320 was launched. The A330/A310 are the only Airbus aircraft that are controlled in the traditional sense. The issue with the A300-600 rudder was that it was more sensitive due to some changes Airbus made. It was established during the investigation that the AA pilot controlling the aircraft was too aggressive with the rudder pedals (as per AA training) and the forces generated caused the rudder to exceed ultimate load and break away from the aircraft. All subsequent rudder issues have been established to be caused by bonding issues in the composite structure due to poor maintenance or incorrect inspection times given by Airbus. Following investigations inspection times have now been modified and no further incidents have occurred.

The ADIRU's in the QANTAS A330 where found to be operating perfectly well during subsequent analysis, which has now led investigators to look at out outside influences. The ADIRU is not unique to Airbus and is not made by them.

It's far too early to say what caused the crash of flight AF447 so linking this to 'possible flight control issues' is unwise at this stage. Any number of possibilities could have brought the aircraft down.

As with any computer programme, its only as good as the humans make it. I doubt Airbus 'quietly' modified the sensors following the 1993 Lufthansa incident. If this was found to be the cause then Airbus would have been made to do it and of course they would have had to let airlines know about the modification otherwise how could they install it on existing aircraft?

I agree that pilots are becoming too reliant on aircraft software in general. This is not limited to Airbus aircraft though.