737 NG FMC and SP-LKA
 

When one of the pilots entered the wrong location before takeoff, the FMC display went blank and the crew assumed a failure of the FMC.

Would it not be better in such a case if the display screen, in additron to blanking out the attitude and heading information, also displayed some message indicating why there was no information, such as "Incorrect data entry"?

I know that the procedures for restoring the display are in the books, and should be in at least one pilot's head, but when screens go blank pilots, superstitious beasts that they are, sometimes suspect the hardware went bad.

The FMC will give you a scratchpad message saying that it thinks the position is wrong if it is over a certain distance from the last known position. In this case heading/attitude info will still be displayed.

However, they apparently tried to re-align the IRS during the taxi out to the runway. As they moved during this realignment, it failed and thus the heading/attitude info was lost.