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Thursday, April 10, 2014

Making Autopilot Systems Safer

Woodrow Bellamy III 

[Avionics Today April 10, 2014] Would you believe that just 30 lines of computer code might have saved Air France flight 447 from crashing into the Atlantic Ocean in 2009? Carlos Varela, an experienced pilot and associate professor of computer science at Rensselaer Polytechnic Institute, believes so. Through funding from the Air Force Office of Scientific Research, Varela and his research group developed a computer system that detects and corrects faulty airspeed readings, such as those that contributed to the Air France crash.

Analysis of the AF447's recovered flight data recorder box revealed that a chain of events beginning with erroneous readings from the pitot tubes — instruments that use air pressure to calculate airspeed, according to Varela. The pitot tubes, which the group believes were blocked by ice, reported a drop in airspeed from 461 to 182 knots. The autopilot, unaware of the error, lowered the nose of the airplane in an attempt to increase airspeed. Unable to maintain altitude, the autopilot disengaged, at which point three human pilots were unable to correct for the error. 
 
The Rensselaer Polytechnic Institute (RPI) research group concluded that there was a failure in the airspeed sensors, which Varela as a pilot says is a commonality. To correct this, they've developed a programming language called the “Programming Language for spatiO-Temporal data Streaming applications,” or “PILOTS,” which treats air speed, ground speed and wind speed as data streams that sometimes exhibit errors that can be automatically corrected and reproduced so that the pilot receives the correct readings and can adjust accordingly. 
 
 
Pitot tube from an Airbus A380. Copyright © 2007 David Monniaux.
 
"We actually put all the data from the flight recorder in Air France 447 into our models and our computer software and we were able to recover the [correct] airspeed in 5 seconds," said Varela. "We know in aviation you have to learn from accidents to prevent future tragedies. If the software were to be included in future flight systems, we would avoid this kind of accident, I think," said Varela. 
 
Eventually, Varela wants to "scale up" the prototype software to be able to read the hundreds of data streams that actually occur within a commercial flight. 
 
In May, Varela will demonstrate his research on enhancing the safety of autopilot systems to the aerospace community during a presentation at MIT. The pilot/scientist hopes that avionics manufacturers will use his prototype to build safer flight systems in the future. 
 

"I would love it if avionics manufacturers, aviation companies can take this type of work and make our flights safer," said Varela. "I haven't honestly explored commercial applications myself, but this paper is out in the public domain so people can take use of them and hopefully build safer flight systems." 

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