Cannot start APU

[davidz 26]

If you let the APU run the tanks dry, it will fail ;)

[Spin737 102]

Right for the first, wrong for the second.APU has nothing to do with CAT III.

It can if one of your IDGs fail. That's another favorite trick for sim instructors: Oh no! You've lost a gen and it's below CAT1. What can you do?

[davierosoft 13]

It can if one of your IDGs fail. That's another favorite trick for sim instructors: Oh no! You've lost a gen and it's below CAT1. What can you do?

In that case if IDG fails the aircraft loses the CAT III capability, if it doesn't the aircraft is still capable.MEL reports only about extended reange operation.PS: Apu inop can be removed and the aircraft is capable to fly without it (without losing CAT III)Obviously, if something else will happen that reduces the ability to perform a cat operation, it will be the cause. Not directly te APU.It must be fixed in 10 days.

[Spin737 102]

In that case if IDG fails the aircraft loses the CAT III capability, if it doesn't the aircraft is still capable.MEL reports only about extended reange operation.PS: Apu inop can be removed and the aircraft is capable to fly without it (without losing CAT III)Obviously, if something else will happen that reduces the ability to perform a cat operation, it will be the cause. Not directly te APU.It must be fixed in 10 days.

I think we're saying the same thing, but to make sure for everyone else: en route, if you lose an IDG, you can still do a CAT3 if the APU GEN is operative. Not quite on topic, but still interesting.

[ZachLW 37]

Right for the first, wrong for the second.APU has nothing to do with CAT III.

Thanks Andrea. I was unsure.

[davierosoft 13]

Thanks Andrea. I was unsure.

;)

[davierosoft 13]

I think we're saying the same thing, but to make sure for everyone else: en route, if you lose an IDG, you can still do a CAT3 if the APU GEN is operative. Not quite on topic, but still interesting.

A bit OT, but, in case of both IDG failure, you have a single power source powering both A/P (the APU gen). Not sure if cat III is still allowed (by regulations) as for redundancy and to presvent missmatch in calculations, during approach the FCCs use independent power sources, APU provides power to both at the same way. If power is not good and is able to create nuisance in both FCCs, they can do same errors.There is a remote possibility that it could be happen, but, as boeing provided this security system in normal condition, APU will override it and MAYBE it is not allowed by regulations.

[davierosoft 13]

Hi talk about odd things I was doing a flight when I noticed that fuel was only dropping on the centre and right tanks. The centre tank was low and I had turned the centre pumps off. I even turned the right pumps off for awhile but the left tank would not budge. I have the time base failures on, Standard I think. I did go into the FMC and settings and looked to see if I changed something by mistake. Not sure if I did, might put it down to ice . I have a feeling I might have left the Anti Ice off. It did come right though but landed with a fuel inbalance.

That is a bug of the NGX when simulating fuel scavenge system.The real one starts to transfer (automatically and cannot be stopped) fuel from center tank to the left tank when the wing has half fuel (around 2000Kgs).On the real the transfer rate is about 100Kg/h, normally is always below 200Kg/h.In the pmdg this rate is something like 20Kgs/min. Something like 1200Kg per hour. This as you can see is too much. Unbalance will occur in few minutes.The problem can be seen only if you have fuel in center tank, normally if previously filled, the center tank fuel is used before wing tanks. This means that using it as supposed, you will never see too much imbalance.You will see at idle that left tank is growing, right one is dropping, same for center tank.To prevent problems, let the center tank pump running from APU running to LOW pressure light.Why using a center tank pump when APU is running? Because pressurizing center tank left pump will let the APU use the fuel from that tank. This preventing imbalances when on ground.

[BillCusick 75]

Sadly, several here will not understand the reference...

Oh, that was sneaky !..but I dunno what that means, honest Regards