Some questions before release

[Chock 17,769]

But in the real world, wouldn't the bulk of those 45 minutes usually be on ground power?Tom

Probably, but not when you are on the deck at nowheresville, with no ground carts, or plugs at the stands, which is after all why the 737 was given an APU and airstairs in the first place.Al

[Guest Tamadeez]

Budget airlines actually have Bicycle pedals for all the passengers to power the pilots preflight

[Guest cassis]

It actually vaporizes it, so no.

... "vaporizes" ? we said no comments about release date please !

[Jack_C 1]

I do not know whether other companies start the APU once airborne, though I would imagine there aren't many. We usually start the engines off of APU bleed air, so it is already running on the ground. As for the fuel, I just looked in the manual, and I can't find anywhere that gives the APU fuel burn rate. But operationally, that would be factored into the dispatch release. Regardless, the APU fuel burn is negligible compared to the CFM56's. David Lynn

A good reason to have it started on the ground rather than just before ETOPS entry is that it is common for the APU to not want to start at high altitudes apparently. A while back I had to fire it up at about 32,000 feet and I got a FAIL light illuminate. Going by the checklist it says to wait 5 minutes before attempting another start. By that time we had descended through 25000 feet and then second start was successful. I was chatting with other pilots later on and they asked me at what altitude were we at when I got the failed started. After telling them they had said that it is common at higher altitudes for the APU to not want to start. So if you were at FL360, or so, and went to start the APU before ETOPS entry and it didn't start, you would have to descend, start the APU, and then climb. Waste of fuel. Better to just start it on the ground.JackColwill

[dlynn91 0]

A good reason to have it started on the ground rather than just before ETOPS entry is that it is common for the APU to not want to start at high altitudes apparently. A while back I had to fire it up at about 32,000 feet and I got a FAIL light illuminate. Going by the checklist it says to wait 5 minutes before attempting another start. By that time we had descended through 25000 feet and then second start was successful. I was chatting with other pilots later on and they asked me at what altitude were we at when I got the failed started. After telling them they had said that it is common at higher altitudes for the APU to not want to start. So if you were at FL360, or so, and went to start the APU before ETOPS entry and it didn't start, you would have to descend, start the APU, and then climb. Waste of fuel. Better to just start it on the ground.JackColwill

Yep, the manual states in the limitations section that a successful start is not assured above FL 250. David Lynn

[Vollie 11]

Budget airlines actually have Bicycle pedals for all the passengers to power the pilots preflight

Yes I can just imagine that now straight in front of me, no one of the passengers can refuse to cycling if the pilots were asking that!! :(

[LufthansaPilot 0]

I have another video, showing that Ice can really gather on the wing of a 737.http://www.youtube.com/watch?v=Rczi0TJ05YA&feature=channel_video_titleCheers,Emir Y.

[Houghton11 12]

I have another video, showing that Ice can really gather on the wing of a 737.Cheers,Emir Y.

I can't find anything in the vid description that say's the video's from a 37. I don't think there's VG's that near the tips of the wings in the RL aircraft. I don't know much about anything 37NG...so I could be mistaken.

[NGXfanatic 85]

At what time do most of you all start the APU at the gates, assuming you were on GPU air/power for the majority of the preflight setup. I'm talking about major airports in the US/Europe, not east Jabit where there is no ground support.I shoot for about 10 minutes before start, and when you factor the pushback/engine start phase to be about 5 minutes max, that leaves me with about 15 minutes total APU time on the ground. That 15 minutes total time is what I aim for with all my addon planes, but I am curious about matching real world practice for the NG. Would it make sense to save fuel and start the APU at 5 minutes before start? It's a small amount of savings, but you know the airlines will take every little bit of savings because its adds up over time.

[rgamurot 1]

At what time do most of you all start the APU at the gates, assuming you were on GPU air/power for the majority of the preflight setup. I'm talking about major airports in the US/Europe, not east Jabit where there is no ground support.I shoot for about 10 minutes before start, and when you factor the pushback/engine start phase to be about 5 minutes max, that leaves me with about 15 minutes total APU time on the ground. That 15 minutes total time is what I aim for with all my addon planes, but I am curious about matching real world practice for the NG. Would it make sense to save fuel and start the APU at 5 minutes before start? It's a small amount of savings, but you know the airlines will take every little bit of savings because its adds up over time.

I guess it really just depends on the company or even how long they'll be on the ground. The interisland flights here (mainly 717's and CRJ's) never use GPU's. Some other airlines won't use GPU's if their stopover is less than 90 minutes. Some will no matter how long their stay is. But I've been told a lot of the time they will use the APU because it's actually cheaper than using ground air.

[Airbus Commander 563]

At what time do most of you all start the APU at the gates, assuming you were on GPU air/power for the majority of the preflight setup. I'm talking about major airports in the US/Europe, not east Jabit where there is no ground support.I shoot for about 10 minutes before start, and when you factor the pushback/engine start phase to be about 5 minutes max, that leaves me with about 15 minutes total APU time on the ground. That 15 minutes total time is what I aim for with all my addon planes, but I am curious about matching real world practice for the NG. Would it make sense to save fuel and start the APU at 5 minutes before start? It's a small amount of savings, but you know the airlines will take every little bit of savings because its adds up over time.

Most airports I fly to require that the APU be turned off and the GPU instead be used. Typically we aim to start it 2-3 mins before pushback...

[NGXfanatic 85]

I guess it really just depends on the company or even how long they'll be on the ground. The interisland flights here (mainly 717's and CRJ's) never use GPU's. Some other airlines won't use GPU's if their stopover is less than 90 minutes. Some will no matter how long their stay is. But I've been told a lot of the time they will use the APU because it's actually cheaper than using ground air.

You know what, I remember reading somewhere that the ground air is "expensive". I guess even with the fuel being used by the APU, it can work out to be less costly than ground supplied air. I was always under the impression that the APU was the costlier option of the two, now I have learned something new!

Most airports I fly to require that the APU be turned off and the GPU instead be used. Typically we aim to start it 2-3 mins before pushback...

And that explains the non-monetary cost of APU use, even though it is cheaper than the GPU: the noise cost. Much like how MD-11/DC-10 operators are told to avoid using the tail mounted engine on the ground, for noise abatement considerations APU use is restricted at most busy airports to a maximum time of about 30 minutes or less, from what I've observed by reading airport charts. I'm going to now start putting the APU online 5 minutes before pushback in my sessions.Thanks for the replies!

[Kobradelta1000 0]

Forgive my "novice " POV here, but there is no RAT on the NGX- instead you use the Apu..What if you run out of fuel?- is this the same new thing as the "excellent" digitalized backup instruments?- could someone explain it to me please- Thnx

[Chock 17,769]

The standby flight instruments use different sources from the main ones, to allow for some system redundancy. What source they actually use depends on which type is fitted.The old 'steam gauge' ones (pre 2003 NGs) use auxiliary pitot and alternate static sources instead of the ADC/ADIRU. One of the noises you can hear on the flight deck (if it isn't too noisy) is the vibration system motor on the standby altimeter, which shakes the internal workings of the gauge ever so slightly in order to prevent the cogs inside the thing from lagging or sticking. Fifty quid says PMDG have modeled that.The more recent Integrated Standby Flight Display (i.e. the one that looks like a mini PFD) is powered by its own dedicated battery that is independent of the main systems, which is normally kept charged by power from the regular systems, i.e. you can't actually switch the ISFD off at all from the cockpit and it will keep going even if all the fuses on the C/B panel pop because of a direct connection to the battery. The battery for the ISFD will allow it to run for two and a half hours if every other power source fails, so it needs neither the engines nor the APU in order to work.The ISFD is not just for an emergency though - it sends its data to the flight computers, so on a high category approach and landing, it is in fact one of the sources where the data for the landing autopilot control inputs is coming from.Question is, given that many people seem keen on the idea of breaking their shiny new NG, which propeller head will be the first one to cut all the power, sit for 150 minutes and see if the ISFD cuts out, then complain about a lack of realism if it doesn't? :( Al

[Kobradelta1000 0]

Thanks for your detailed explaining, Alan!!! - and i´m sure, there are more people out there who will try this sort of failure :(