Ask Captain Lim

Dear Captain Lim,

I was reading this in a flight magazine (5/9/05), about the AIDRU (something like that, I think - it?s to do with the auto pilot) of a Boeing 777 which suffered a malfunction. The report further went on to say that, the relevant authorities have issued a directive to all operators on this problem. The manufacturer responsible is working to fix it.

It also said that a failure of this system could have had very serious results. I think (not quite sure though), that it could bring the plane down in flight.

As you can imagine from a nervous flyer (which very much I am) point of view, it is very distressing. So could you please (if you are aware of this) reassure me of this; what is the problem exactly and which airlines have fixed it? This would help me a great deal when I will need to fly the next time.

Many thanks.

Jaz S Dhaliwal.

Hi Jaz,

It is true that a Boeing 777 did have a malfunction on one of its major flight system (ADIRU - Air Data Inertial Reference Unit). I believe all the airlines operating the Boeing 777 have implemented the fix-up of this very important component as this information was widely circulated to every affected carrier.

The ADIRU provides many data to the pilot. Computers in the plane use these to provide much vital in-flight information such as: attitude, speeds, position, heading, wind velocity, rate of climb or descent, etc. Although the design of this unit is supposed to be fault-tolerant (Murphy Law?), it did suffer a fault causing the computers to go haywire.

So, could the ADIRU failure bring the plane down? Not likely. Remember, pilots are well trained to take over when the computers fail. This is a typical case of such a situation. The pilot did land the plane safely after disconnecting the autopilot and other controls that rely on the ADIRU.

Wish you a safe flight.