IRU allign in flight

[WAD3 0]

I was on a flight from Kai Tak to Dubai when I lost the IRU allign. I had to no choiuce but to stop my flight and save then I returned and in that process I lost the middle IRU allign. No doubt this was due to saving and restarting the flight. What I need to know is it possible to re-allign in flight? The other two IRU are working fign so I think I can complete the flight just wondering what I could do for the third IRU.ThanksAndrew DeLaney

[Check_Airman 3]

Not possible. The aircraft must be stationary for the duration of the IRU alignment. Boeings have an ATTitude mode which would have returned your attitude, true heading, and VS, but MD didn't add that feature.If you lost one IRU, you could have continued the flight by switching seats, or by selecting the AUX IRU.Paul

[KCA9304 0]

Not possible. The aircraft must be stationary for the duration of the IRU alignment. Boeings have an ATTitude mode which would have returned your attitude, true heading, and VS, but MD didn't add that feature.If you lost one IRU, you could have continued the flight by switching seats, or by selecting the AUX IRU.Paul

Paul,Just for the record:Correct to say that MD did not add the feature to select the ATT mode.In the MD the Attitude mode is selected automatically when the NAV functions are lost.This will be indicated by a LVL 1 alert: IRU_NAV FAIL and several warnings on the ND.Ref: Systems> INST 10.17 and INST 40.1Switching to AUX is the way to deal with it like you say correctly, to restore the ND data.Also the (nav) failing IRS should not be switched off, as it is still feeding acceleration signals into various systems such as Autobrakes.Regards,Harry

[Check_Airman 3]

Thanks Harry.I'll have to check the manuals and see if magnetic heading can be displayed if NAV is lost.Paul