Expert: Laura Laster - 6/8/2009

Question
In the light of the recent Air France crash, media often cite experts something like this: Part of the problem could have been broken speed sensors (apparently Airbus had issues with those) and thus wrong data being fed to the flight computers.

Is this possible? If I were an aeronautics engineer, I'd wire up GPS at least as a secondary source for speed data e.g. to double check and alert the pilot if the speeds mismatch significantly.

Is this the case or is GPS only used for getting a fix on the location?

Another thing is also quite bizarre to read: Airplanes send system status messages via satellite to the airline so they can prepare the ground team for necessary repairs ahead of time. At the same time planes are lost and only found many days later because their exact position is unknown in those big areas without radar coverage. I take the pilot radios the position every now and then, but why not use the system status satlink to update the position let's say every few minutes?

Answer
Hello,
I can try to answer at least parts of your questions. While I don't know much at all about avionics or the speed sensors & flight computers on Airbus (or any) aircraft, I think it could be plausible that a speed sensor sending incorrect data to the flight computers could contribute to an accident. However, I would also think that any complex aircraft would have multiple speed sensors and that a computer would be cross checking the sensors and produce an error message if there was a problem. Again, I'm not an expert on this.

I don't know if GPS is used as a secondary source for speed data for this aircraft.

Regarding satellite system messages and position: in the King Airs my company operates, we have a system called SkyConnect which sends a position report every 1 minute whenever the airplane is flying below 10,000' MSL and every 5 minutes whenever the airplane is flying above that altitude. These time intervals can also be changed by the operator of the aircraft by adjusting the internal settings on the SkyConnect system in each aircraft.

This is intended to help us narrow down the position of the aircraft in the event of an accident. The system is different than what was installed on the Airbus in the accident, I am sure. This system doesn't send us reports of any problems the aircraft has, but it does let the pilots send us 32 character text messages and also someone on the ground to send text messages to the aircraft. So, the capability is available to have continuous monitoring of aircraft using satellites and a system like we have (connected to the aircraft's GPS). This also has a satellite phone integrated to the cockpit so the pilots can call anywhere while they are flying, and we can also call the aircraft when it is flying.

I hope this helps you, and I'm sorry I don't know more about this particular subject.

Laura