Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
convair880mfan
Topic Author
Posts: 253
Joined: Fri Jun 25, 2021 12:33 am

Which airliners are able to use APU while airborne?

Sat Oct 02, 2021 9:48 pm

According to author Jim Upton in his book, "Lockheed L-1011 Tristar" :

"Providing ground self-sufficiency and emergency in-flight power, the (L-1011) APU system is operable up to an altitude of 30,000 feet under all flight conditions within the aircraft operation envelope." (1)

Are there other aircraft that can use the APU while airborne or can they all? Thanks.

________________________
(1) Jim Upton. Lockheed L-1011 Tristar, in Airliner Tech Series Vol. 8. North Branch, MN: Specialty Press, 2001. p. 28.
 
GalaxyFlyer
Posts: 8602
Joined: Fri Jan 01, 2016 4:44 am

Re: Which airliners are able to use APU while airborne?

Sat Oct 02, 2021 10:19 pm

Just about all of the twins can, the B727 and B747 couldn’t.
 
convair880mfan
Topic Author
Posts: 253
Joined: Fri Jun 25, 2021 12:33 am

Re: Which airliners are able to use APU while airborne?

Sat Oct 02, 2021 11:11 pm

Did the Lockheed C5 Galaxy have an APU and could it be used in flight, GalaxyFlyer?
 
GalaxyFlyer
Posts: 8602
Joined: Fri Jan 01, 2016 4:44 am

Re: Which airliners are able to use APU while airborne?

Sat Oct 02, 2021 11:42 pm

Two APUs, L and R. Useable in-flight but could cause paint damage from the exhaust on A models, larger shield on B, IIRC. Little need to run one in flight, 10 hydraulic pumps, two off bleed air, 2 per engine. Four generators plus hydraulic emergency generator.
 
BoeingGuy
Posts: 6679
Joined: Fri Dec 10, 2010 6:01 pm

Re: Which airliners are able to use APU while airborne?

Sat Oct 02, 2021 11:57 pm

GalaxyFlyer wrote:
Just about all of the twins can, the B727 and B747 couldn’t.


I thought the 747 APU could be used in air; it just couldn’t be started in air.
 
GalaxyFlyer
Posts: 8602
Joined: Fri Jan 01, 2016 4:44 am

Re: Which airliners are able to use APU while airborne?

Sun Oct 03, 2021 12:44 am

That maybe true, but not starting airborne is a pretty severe handicap.
 
Flow2706
Posts: 315
Joined: Sat Jan 28, 2017 7:20 pm

Re: Which airliners are able to use APU while airborne?

Sun Oct 03, 2021 5:32 pm

On the A320 APU can be started and run up to the service ceiling (39800ft or 39100ft, except for some ACJs). The generator can be used at altitude as well, it has the same rating as the engine generators. APU bleed usage is limited to around 20000 or 22000ft (depending on APU type) and APU bleed may not be used for wing anti ice (as it is too cold).
 
gregorygoodwin
Posts: 94
Joined: Wed Jun 11, 2014 10:01 pm

Re: Which airliners are able to use APU while airborne?

Mon Oct 04, 2021 2:34 pm

Does the APU have to be able to start and run during flight have anything to do with being category 3 flight able?
 
Woodreau
Posts: 2175
Joined: Mon Sep 24, 2001 6:44 am

Re: Which airliners are able to use APU while airborne?

Mon Oct 04, 2021 3:39 pm

You need two independent electrical sources. So an inop APU doesn’t preclude Cat III operations.

If you only have a single electrical source, i.e. IDG 2 disconnected with an inop APU the equipment review for Cat III operations allows Cat III Single (fail passive) approach but not a Cat III Dual (fail operational) approach.


Edit: for an A320 series aircraft I don’t know how other aircraft are impacted.
 
Max Q
Posts: 9126
Joined: Wed May 09, 2001 12:40 pm

Re: Which airliners are able to use APU while airborne?

Tue Oct 05, 2021 8:37 am

MD80, 757 and 767 APU all run and can be started in flight. The latter two can be used for electrical needs up to the aircraft ceiling




If dispatching with an engine driven generator inop we would power that side with the APU generator and it would be left running for the entire flight


We’d occasionally get requests from maintenance control to start the APU halfway through a long haul flight. Even after five hours cold soaking at high altitude they always started up immediately


On an autoland approach we would start the APU as a back up in case one aircraft generator failed
 
bigb
Posts: 1513
Joined: Fri Nov 07, 2003 4:30 pm

Re: Which airliners are able to use APU while airborne?

Tue Oct 05, 2021 9:10 am

BoeingGuy wrote:
GalaxyFlyer wrote:
Just about all of the twins can, the B727 and B747 couldn’t.


I thought the 747 APU could be used in air; it just couldn’t be started in air.


This is correct. It is only available for bleed air up to 15,000. Mainly for Pack to APU takeoffs. After 15,000 it is no longer available for air but can stay on until 20k. However, it can not be started in the air. This is for the 747.

Apparently, APU starting inflight on the 747 wasn’t certified, hence the limitation.

Who is online

Users browsing this forum: TOGA10 and 16 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos