Does anyone has experienced that APU won't start on some flight in 747-8?

It's starting normally  like in 10 flight around 2-3 flight that it won't start or take a long time to fire it up.

Holding in start for 3 seconds?

12 hours ago, Suthiphan said:

Does anyone has experienced that APU won't start on some flight in 747-8?

Everyone does.

The APU cannot be started in the air in the 747 (the real one, too). You don't need it, and running it presents an extra (an unnecessary) fire risk.

It’s interesting how Boeing created this logic preventing APU inflight starts on the 748.  Most airplanes will either have a restriction or limitation written in the manuals, but it could still be started.

5 minutes ago, icaruss said:

It’s interesting how Boeing created this logic preventing APU inflight starts on the 748.  Most airplanes will either have a restriction or limitation written in the manuals, but it could still be started.

Most airplanes have altitude and speed limitations, but still allow it because the extra gen could be handy. When you have 4 engines, not only would it be rare to lose enough to need the APU, you also get enough off of windmilling engines to keep things going.

Beyond that, you have to - as mentioned earlier - factor in the long legs of the plane versus the fire risk of allowing it to be run (again, keeping in mind the decreased likelihood in light of the additional engine gens and windmilling, even if they're not turning under power).

Not just the 748, btw - 744, too.

It happened me yesterday (on the ground). 

28 minutes ago, Jude Bradley said:

It happened me yesterday (on the ground). 

Usually a result of not holding it there for a second or two. 

That or a failed APU. Willing to bet this is a false positive, unless you see it again and have more specific steps to repro.

For sure I'll test again. 

 

No problems this time. I'll let you know if it happens again.

 

3 hours ago, Jude Bradley said:

No problems this time. I'll let you know if it happens again.

 

Thanks!

I cannot get the APU to start, same aircraft after completing a flight yesterday, despite holding the APU start knob for more than 5 seconds, despite no Failures set. Any ideas, Kyle?

2 hours ago, vc10man said:

I cannot get the APU to start, same aircraft after completing a flight yesterday, despite holding the APU start knob for more than 5 seconds, despite no Failures set. Any ideas, Kyle?

How long are you waiting after releasing the switch?  There is a delay.  Watching the MFD Status screen?  In all the testing and now in all the new users you are the only one reporting a problem starting the APU... trying to figure out why would be easier if you were more verbose in your problem descriptions. "After completing a flight," I assume means you have landed and you are starting the APU as you taxi to the ramp?

Dan, permit me to elaborate.Last night, flew my 747-400 before applying today's micro-Update. Had no problems with GPU on powering everything up prior to push-back by GSX when I go to the APU start switch, turn it on and hold for about 4-5 secs, then release and sure enough it came on.. Additionally, I did not have any error messages being flagged up on the Hydraulic switches.

Today, I applied the micro-Update from within OC, decided to use the same livery from the same airport I landed at last night. That's when I doing the same routine of turning on the APU I noticed no matter how many seconds I held it to Start it just would not come one. Additionally, Hydraulic Pumps 1 and 4 were now showing System Faults where I had none yesterday. That got me thinking into maybe I should do a Maintenance refils but even doing that got me nowhere.

In the end, I turned the sim off, re-started and this time ran the APU only power up from the BAT, and it came on after the usual holding the Start switch on.

2 hours ago, vc10man said:

Today, I applied the micro-Update from within OC, decided to use the same livery from the same airport I landed at last night.

Does this mean you saved last nights scenario and loaded it today after running the micro-update?  Along with the spurious EICAS messages I would say that this was definitely a panel state problem.  I know during a beta test when we might go through a dozen or more builds the best thing to do is always remove old panel state files.

No, did not use previous flight's scenario. A completely fresh scenario after the micro-Update. Was using the default start panel, i.e. GPU available.

Will have another go at it as ran out of free sim time yesterday.