Hi,

 

I got this warning on the EICAS on 2 occasions just after take-off. It's really weird that such a warning would appear during the initial stages of the flight.

 

Both flights were done on heavy payloads with GW of around 380000kg. Flights with lower weights are uneventful and the warning does not appear.

 

The warning that stays during cruise and doesn't go away. I'll report back during landing if it clears itself.

 

Any ideas?

 

 

Any ideas?

 

Sounds a lot like the aircraft isn't being configured properly. If you haven't flown the tutorial, please do so. Additionally, make sure you go through your pre-flight carefully. There are a number of steps that are slightly different within the 744 fleet (pertaining to FMC options), and slightly different from the 737 and 777 that can trip you up.

Did you also get a split IRS message on the CDU? I got that along with a no land 3 a few times I have tested the bird.

Did you also get a split IRS message on the CDU? I got that along with a no land 3 a few times I have tested the bird.

 

Ah yes I did! Both flights I made the mistake of disconnecting ground power before switching to the APU GENs. Got the Split IRS message after switching power to the APUs and went ahead with my pushback..etc, didn't think much about that message.

 

Could that be the cause?

 

 

 

I'll look through the tutorial to see if I missed anything. 

 

 

Both flights I made the mistake of disconnecting ground power before switching to the APU GENs.

 

This is why. Fully power down the IRSs, and then re-spin them.

Just out of curiosity, why does this cause the autoland to fail? Don't the IRS' just keep humming along on DC power when you screw up the gen config?

Because when AC power is OFF the LEFT and RIGHT IRS units draw DC from the battery while the CENTRE IRS drops (there is an automatic relay to conserve battery). The only case that the CENTRE IRS will draw DC power is if DC BUS 3 is NOT powered and then only for 5 minutes.

 

There is your technical explanation.

Ah yes I did! Both flights I made the mistake of disconnecting ground power before switching to the APU GENs. Got the Split IRS message after switching power to the APUs and went ahead with my pushback..etc, didn't think much about that message.

 

Could that be the cause?

 

 

 

I'll look through the tutorial to see if I missed anything. 

You are not alone, I took off from KPAE with "no autoland 3": and message:  "IRS align mode C".

According to the POS REF page (3/3) IRS L and R showed some numbers, but C was empty. 

 

Now after reading this post this all makes sense, Ik made the same mistake playing around with the power. 

 

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?

(I used to fly Ralph Tofflemire classic 747 with the simufly INS, if you had 3 working INS units, you could have your nav checked via VOR's (triple mixing; if one unit failed - it happened!! - the triple mixing was gone).

 

Regards,

 

Wijnand Lindelauf  (EHBK)

Did you also get a split IRS message on the CDU? I got that along with a no land 3 a few times I have tested the bird.

 

Had that myself, I think it has something to do with losing power temporarily - resulted in me getting the No Land 3 message too.

 

EDIT:

I can see it is already discussed in detail above. My bad.

So how to solve it during the flight.I still can't figure it out.

I received this message at the beginning of the tutorial flight (except that I started with ground power connected at a gate and IRSs not aligned) and continued to see it throughout the flight.  I had accidentally turned off the right IRS after all three were aligned while still on ground.  I did turn it back on and thought it was on long enough to realign, but I continued to get this message.  I didn't know how to tell if the third IRS had realigned.   On arrival I received "Land 2" message instead of "Land 3" (I chose a manual landing as I usually do). 

 

Mike

I know this is an old topic, but I was wondering if there is a fix if I mess up.

On Pushback, I disconnected ground power (By mistake) without having the APU supply power and got a temp blackout until I hit the APU power bus switch.   Now "No Land 3" shows up.  And yes the IRS #2 differs from IRS 1 and 3.

So now I take off - still with No Land 3 showing.  Is there any way to get rid of that?  Can't re-align IRU at 340 KTS?  

2 hours ago, paulyg123 said:

So now I take off - still with No Land 3 showing.  Is there any way to get rid of that?  Can't re-align IRU at 340 KTS?  

Shouldn't have taken off in the first place. The only way to fix it is to re-align the IRS, which you can't do with the plane moving at all.

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.

 

Hi, I think the problem here is that you’ve switched the IRS to off first before you’ve selected ATT.

If you lose an IRS switching from NAV to ATT in flight and entering a heading in the CDU allows the IRS to sort itself out enough to  enter a degraded state of functionality and provide attitude only information.

However once you turn the IRS to the off position  you’ve lost it completely, it requires  a full realignment to restart ,which can’t be done in flight, or with any motion detected.