Originally Posted by
alf5071h
From the accident report, when the HUD reverts to upset mode, the mental reference has to change from FPA to attitude; - this requires significant mental readjustment. Also the FD is removed.
An X-15 was lost when the attitude target indicator on the artificial horizon was left in yaw mode for ascent rather than in sideslip mode for re-entry (or was that the other way round?) due to high pilot workload because of other issues. The re-entry was thus flown at the incorrect angle resulting in loss of control and the breaking up of the aircraft. The NASA Dryden historical document I read some time ago says something along the lines of "although not mentioned in the final report, several engineers came away with the message that the same instrument should not be used to display conflicting information at different times".
Seems that some lessons have to be re-learnt every now and then.