View Full Version : Use of the APU on stand

Skipness One Echo
8th May 2018, 08:45
What are the rules on APU use over the summer months if an aircraft is just sitting in the sun on a 90 minute turn around. Do they make the cleaners work in a non cooled environment? I know some airports are really strict on this (hello LCY) but does runnning an APU really make any dent in pollution or noise when compared to jet engines?
Is non use of the APU a legal thing or part of the Ts and cs which vary by airfield?

8th May 2018, 08:50
Is non use of the APU a legal thing or part of the Ts and cs which vary by airfield?

As you have noted some airports are very "hot" ;) on APU useage based on emissions and noise poicy, some less so..There's also sometimes a question (from the airlines POV) of whether it is cheaper/allowable to run the APU or shut it down and instead pay for airport supplied ground air and electrics.. Fundamentally it varies from airport to airport (we carry the company preferred preference for each airport in our route network in our onboard documentation).

That said you may have use bit of discretion and engage in a bit of negotiation if dealing with high cabin temps.

8th May 2018, 09:28
It varies from airport to airport and operator to operator.

An example, Stockholm are very insistant that APU use is kept to a minimum, so much so that when 787s began to land there the airlines had to negotiate a special exemption to allow APU to be used throughout the turnround.
The 787 APU at the time had a 'bowed rotor' problem which meant if it was shut down it couldn't be restarted for a couple of hours.
B787 APU Heating Issue (http://aviationweek.com/awin-featured-story/boeing-tackles-787-apu-heating-issue)
Operators have discovered that after the APS5000 APU is shutdown with the inlet door closed after landing, heat continues to build up in the tail compartment. After some 20 min. this causes the rotor shaft to bend or ‘bow’, and the shaft takes up to two hours to straighten back out.
As many 787 operators, including All Nippon Airways (http://awin.aviationweek.com/OrganizationProfiles.aspx?orgId=12397) (ANA), have flown the aircraft on shorter routes with reduced turnaround times, this has resulted in restrictions on when the APU can be restarted. An advisory bulletin from United Airlines (http://awin.aviationweek.com/OrganizationProfiles.aspx?orgId=16430) says that if an APU start is attempted 20-120 min. after shutdown with the inlet door closed, the “bowed rotor shaft can cause turbine rub and significant damage.”

Stockholm does offer very good ground power/AC facilities, unlike some UK regional airports who struggle to get two GPUs on stand and have no AC.

My local airport has no restriction on APU use. Which is just as well in midsummer.

Some airlines demand that their pilots do not start the APU until absolutely necessary (in some cases just 5 minutes before STD). This is not necessarily due to fuel use but APU maintenance hours. The less you use it the cheaper it is to operate especially if you are on an 'on wing' maintenance contract with the supplier.
They do have a get-out of course and it will be in their company docs that if cabin temp becomes uncomfortable then the APU may be used.

8th May 2018, 11:45
but does runnning an APU really make any dent in pollution or noise when compared to jet engines?

An APU is a jet engine.

Piltdown Man
8th May 2018, 12:12
I’ll avoid using the APU everywhere if at all possible. But if faced with an aircraft that is too hot or cold to be inhabited or worked upon I’ll ask to start it. If I’m told that this not possible, I’ll cancel the flight. Permission to start APU not been refused to date,


Lou Scannon
8th May 2018, 13:03
In hot conditions it would be absurd not to use some form of cooling from both the crew and pax point of view. I well remember how on the DC10 when the Apu was u/s, we used the "big APU" ie No 2 engine to keep us cool on the ground.
No one seemed to notice!