Hello.

 

I have had some questions about ground operations for aircraft, about APU usage, A/C carts and beginning taxiing.

 

My first question is, when is usually the APU started and shut down? The way I've been doing it is I start the APU 5 minutes before pushback during departure, and shut it down during de-boarding on arrival. How is it done in the real world?

 

My second question is related to the first one. Do you use Air Conditioning carts on the ground to control cabin temperature when the APU isn't running? I have been attaching it to the aircraft along with the ground power unit.

 

And finally, do you have to wait for the "Cabin Ready" signal before starting taxi?

 

Thanks in advance.

At Heathrow (EGLL) the airport rules govern the use of APUs

 

http://www.ead.eurocontrol.int/eadbasic/pamslight-20D2B6204CE50D1882E4F982E6D6BB29/7FE5QZZF3FXUS/EN/AIP/AD/EG_AD_2_EGLL_en_2015-09-17.pdf

Many airports have regulations discouraging, or outright prohibiting excessive use of the APU when parked at a gate, due to noise and air quality issues, so it is typical for aircraft to connect to ground power as soon as possible after arrival at the gate - and to delay starting the APU on departure until just a few minutes before pushback.

 

For the same reasons, it is typical for aircraft to connect to a ground source of conditioned air when at the gate.

 

PMDG represents ground power and air conditioning as stand-alone gasoline or diesel-powered units on wheels, and while these do exist, it is more typical for power and conditioned air to be part of the gate infrastructure at large airports. The conditioned air is usually supplied by a large HVAC unit mounted on or beneath the jet bridge, and there will also be be permanently mounted power cables for supplying 120 volt, 400 Hz, 3 phase AC power, as well as 28 volt DC power.

 

I would think that airports with a "5 minute" APU rule, have provisions to waive that rule if an aircraft is parked at a gate where ground power or conditioned air is inoperative.

It depends on what each company wants their people to do. Generally, though, you can start the APU five minutes prior to departure. Then get ground air and power disconnected. You do not have to run the APU through the entire flight unless there is a mel that directs you to. You can shut it down after all the engines are started. After landing, some operators want the APU restarted during the taxi in so that all engines can be shut down immediately upon block in. The APU can then be shut down after ground power and air are connected. Some want it to stay off, requiring you to keep an engine running until the ground power is connected. Either way, at the gate, ground power and air are usually always connected if available.

 

Yes.

 

No. But you cannot takeoff without it.

At Heathrow (EGLL) the airport rules govern the use of APUs

 

http://www.ead.eurocontrol.int/eadbasic/pamslight-20D2B6204CE50D1882E4F982E6D6BB29/7FE5QZZF3FXUS/EN/AIP/AD/EG_AD_2_EGLL_en_2015-09-17.pdf

I was aware of such rules. But in some airports, like Helsinki (EFHK), the AIP documentation says that the use of the APU is not allowed, yet I still see them using the APU.

 

Many airports have regulations discouraging, or outright prohibiting excessive use of the APU when parked at a gate, due to noise and air quality issues, so it is typical for aircraft to connect to ground power as soon as possible after arrival at the gate - and to delay starting the APU on departure until just a few minutes before pushback.

 

For the same reasons, it is typical for aircraft to connect to a ground source of conditioned air when at the gate.

 

PMDG represents ground power and air conditioning as stand-alone gasoline or diesel-powered units on wheels, and while these do exist, it is more typical for power and conditioned air to be part of the gate infrastructure at large airports. The conditioned air is usually supplied by a large HVAC unit mounted on or beneath the jet bridge, and there will also be be permanently mounted power cables for supplying 120 volt, 400 Hz, 3 phase AC power, as well as 28 volt DC power.

 

I would think that airports with a "5 minute" APU rule, have provisions to waive that rule if an aircraft is parked at a gate where ground power or conditioned air is inoperative.

Thank you very much, your answer is very helpful.

 

It depends on what each company wants their people to do. Generally, though, you can start the APU five minutes prior to departure. Then get ground air and power disconnected. You do not have to run the APU through the entire flight unless there is a mel that directs you to. You can shut it down after all the engines are started. After landing, some operators want the APU restarted during the taxi in so that all engines can be shut down immediately upon block in. The APU can then be shut down after ground power and air are connected. Some want it to stay off, requiring you to keep an engine running until the ground power is connected. Either way, at the gate, ground power and air are usually always connected if available.

 

Yes.

 

No. But you cannot takeoff without it.

Thank you.

 

I seriously thought it was normal for the aircraft to wait 10 minutes after pushback for Cabin Ready.

I was aware of such rules. But in some airports, like Helsinki (EFHK), the AIP documentation says that the use of the APU is not allowed, yet I still see them using the APU.

 

Whereabouts? In the Lido charts (last change 26 March 15) from Helsinki all I can find regarding APU restrictions is a note to "Use GPU whenever possible".

 

As mentioned above, prohibitions are rarely absolute: the normal wording is something along the lines of "If ground power/air conditioning is available, APU usage is limited to X minutes before pushback/after arrival on stand, unless required for heating/cooling the cabin" -- often specifying a range of temperatures outside which it is deemed acceptable to run the APU (OAT below 5C or above 25C is fairly common). There are often different time limits for narrowbodies and widebodies as well (presumably based on the fact that widebodies generally need more electricity to run everything -- which may not always be available from a GPU or FEGP point -- and take longer for the cabin temps to stabilise).

Whereabouts? In the Lido charts (last change 26 March 15) from Helsinki all I can find regarding APU restrictions is a note to "Use GPU whenever possible".

 

As mentioned above, prohibitions are rarely absolute: the normal wording is something along the lines of "If ground power/air conditioning is available, APU usage is limited to X minutes before pushback/after arrival on stand, unless required for heating/cooling the cabin" -- often specifying a range of temperatures outside which it is deemed acceptable to run the APU (OAT below 5C or above 25C is fairly common). There are often different time limits for narrowbodies and widebodies as well (presumably based on the fact that widebodies generally need more electricity to run everything -- which may not always be available from a GPU or FEGP point -- and take longer for the cabin temps to stabilise).

 

 

 

Aircraft parked at the apron shall use ground power always

when available at the stand.

The use of APU shall be restricted only to unavoidable situations

 Source: https://ais.fi/ais/eaip/html/efhk.htm

You are misinterpreting that. All they mean is that you are not to sit at the gate with the APU as your power source if there is GPU available. You need the APU to start the engines and keep the electricity on after you detach from the gate. Leaving the gate is an "unavoidable situation" for APU use. You'll be stranded in a dark and powerless plane if you don't.

You are misinterpreting that. All they mean is that you are not to sit at the gate with the APU as your power source if there is GPU available. You need the APU to start the engines and keep the electricity on after you detach from the gate. Leaving the gate is an "unavoidable situation" for APU use. You'll be stranded in a dark and powerless plane if you don't.

Ah, I see.