NO LAND 3 EICAS warning on take-off?

[berts 97]

On 2/3/2017 at 12:02 PM, wijnand said:

The flight was OK, but I wonder: what would have happend if, in this situation, you would lose GPS for some reason?

Can you safely navigate a longer distance with only 2 IRS'es and no GPS? Or would the nav accuracy degrade in time?

Regards, Wijnand Lindelauf  (EHBK)

The ">NO LAND 3" message means that the triple autoland system is downgraded and is no longer Fail Operational.  However dual channel autolands (Fail Passive) are still possible with this warning present, but to higher weather limits.  As you have discovered, this message will often appear with an interruption to the aircraft's normal electrical power supply.

You can indeed navigate safely with only 2 IRS's working and no GPS, because GPS is not essential to navigate by. The IRU's fitted to the B744/-8 are very reliable and although it is possible for their Navigation accuracy to degrade over time if they do not receive any GPS or DME/DME updates, it is rarely significant enough to cause a problem in flight.

On 11/10/2019 at 3:04 PM, Mangopro said:

I've made the same mistake to disconnect ground power before APU was available and NO LAND 3 message appeared in the EICAS display after takeoff, so i searched for a fix and i discovered the affected IRS was the center one (IRS C), so i switched off the center IRS and another message IRS CENTER appeared in the eicas, so i followed the instruction of the non-normal checklist, i switched the IRS C to the ATT position and since i'm in cruise (with constant speed and altitude) it should work but i'm waiting for more than 10 minutesand nothing is happening so it doesn't seem to be simulated in the PMDG 747-8. Can someone from PMDG confirm it please? Thank You.

You should only switch an IRS to ATT when it is called for in the appropriate QRH checklist. If you had looked in the QRH for the ">NO LAND 3" message you would have been directed to page 4.1.  That was your first mistake!  Switching the IRS C to OFF was your second and even bigger mistake, because it was the reason why you got the  "IRS CENTER" message. Turning the IRS selector to ATT when it is not called for didn't help either , because you could have stayed at cruising altitude all day - even until the cows come home if you like - and you would never have got the Centre IRS to re-align and navigate properly again in this situation. You can only align or re-align the IRS's on the ground when the aircraft is parked.        

[hardstarburst 3]

Ok, so I made the power config error and now have the no land 3 lit. I'd be ok with it if it was just land 1 or land 2 since i'm already in the air. God forbid I have to land it by hand...

[F4RIO 0]

Another (tricky) way this can happen:

Start two engines with one APU generator off, then start the other two. As the switching from APU power to A/C generator power occurs, there is a short period where the IRS loses power, and then: NO LAND 3