Non functioning APU
 

:) Hey all

Just wondering...is it safe to fly if the APU is not working?:)

Normally quite OK, however...MEL restrictions might apply.
For example, with the L1011, flights more than 400 NM offshore are not allowed.
In addition, there is normally an MEL time limit on APU unserviceability...ten calendar days in the case of our aircraft.

Yes, perfectly safe.

It is just a little annoying when it comes to engine start (no compressed air available directly) and air conditioning in very hot conditions (the ground supplied air is usually rubbish) or when there is no ground conditioned air available.

To start the engines without the APU we would get the groundcrew to hook up a unit that supplies us with high pressure air. We use this to start an engine, then push back, rev the running engine a bit and use 'bleed air' from the running engine to start the other engine (talking A320, I'm sure it applies to most jets).

:{ had a bad flight last night with angry pax...stuck in the cabin until the GPU could get the engines started..it konked out and we were stranded onboard in the heat for almost an hr.....:sad: I wish it would just get fixed!!!!! how long is the repair time? on a 737?

The repair time depends on what is wrong with it. It can vary from component change to a complete APU replacement.

In the days when you could be a 'Flight Deck Groupie', I was chatting to the FC of a BA 757 from Arlander to LHR. Apparently the APU was inop and they had to start on the shore line. Ordinarily not a problem, they said, but there was a deal of ice about and the tug couldn't push us back without a lot of difficulty. :uhoh:

ROger.

BTW, you will also need an electrical source:E
(at least on the aircraft I've flown):O
Cheers

Colocolo

Lots of drift. Yes an aircraft operates safetly w/o an APU. It is only an aux source of power if all engines fail or their source of electricty fails. There are backups in thi scenario. To worry about flying in an aircraft W/O an operative APU is not worth the effort.

tiggerpurrrz,

As far as despatch and in-flight is concerned, the APU is a source of AC power along with each engine driven generator. It is a requirement that at least two source of AC power are available. With most twin engines aircraft, if the APU is inop and an engine driven generator fails in-flight then there is only one source of AC power remaining. It is a requirement to divert to the nearest suitable (suitable = performance, facilities and weather) airport.

For most twin engined aircraft with an APU inop on a standard short haul operation with nearby enroute alternates available, it is perfectly safe to depart and perfectly legal. For an oceanic/ETOPs flight it is not safe and I would have thought not legal.

A rather dramatic statement about safety.
As for legality, it is based on the specific airplane equipment. Just check the MEL.

DJ.

Safe but potentially inconvenient and there may be restrictions. For me the biggest issue is during the late spring and summer months when a lack of APU often means no air conditioning. So if it is hot and sunny (remember those days?), I'll only board if I can ventilate the cabin. Otherwise I'll either not take passengers or not take the plane.

PM

Not true. Depends on the aircraft.
A B777 can operate ETOPS with an inop APU, but does have two generators on each engine.

The problems with inop APU are mainly cabin cooling. When I worked for Gulf Air we had a house rule. With APU inop you tried to fix it on the first nightstop. If you failed, you changed it on the second.

The problem here in the frozen North is the difficulty in pushing back an aircraft with engines running over an icy ramp.

[quote]Not true. Depends on the aircraft. A B777 can operate ETOPS with an inop APU, but does have two generators on each engine.[/qoute]
I was careful to say "most" ;) As the 777 was designed with Early ETOPs out of the box I should have known :\

Just out of interest, how many gens does the A340 have? My understanding it is a generator in each of the inboard engines.

:confused: Also noticed on this AC that there was water dripping from above the pax to the left of the control panel for reading & call lights, was only in one location..but could this be condensation and related to the APU inop?

That really depends on the aircraft. The APU isn't available for inflight operations in all aircraft.

Be careful without conditioned airflow with a cabin full of pax. This situation can quickly become an acute health hazard, especially in hot climates. If you can't get ground air conditioning within 15 minutes at places like Jeddah in summer, it's an emergency situation and time to get the pax off the airplane. :ooh:

Yes and no. On a humid day it is common to develope significant condensation in the cold air ductwork. Please give up your obsession with an inop APU. I have personally seen passengers come off an airplane who forced a return to the gate due to condensation dripping out of their air vents HOGTIED!

hmmm...sorry..was not obsessed!!!!..just wanted an answer to a question. I don't think you need to be nasty. I am thinking safety ok.

4, 1 per engine.

A330 can be dispatched on an ETOPS sector with an inop APU as well.

You can't even bring the APU electrics on-line when airborne in a B747-400, so certainly not required.

Four paralled electrical systems - without equal.

I am surprised that the L1011 is SO inferior. Tsk, tsk, 411A, what were Lockheed thinking about - you usually suggest that they are infallible - limited to 400nm from the coast - or did you mean an airport?

On the 727 if the APU is out, you're dead in the water, so to speak. You cannot start the engines or refuel the aircraft unless ground power, GPU, is available and you have an ground air source to start at least one engine.

In fact, unless modified, if you leave an engine running after landing, you still cannot refuel with out a GPU on the 727.

Oh, the APU on the 727 cannot be used in flight, ground operations only.

Yes, suitable overwater diversion airport.
This restriction was so that the airplane would have adequate electrical and pneumatic sources available in the event of a double engine failed situation...IE: same electrical/pneumatic redundancy as a four engine type, where an APU would not be approved for airbourne use (ala---B747).
The L1011 APU can be used (and is fully approved) , for both electrical and pneumatic sources, up to FL 310.

So, four engine redundancy, with a three engine airplane, with regard to electrics/pneumatics.

One should also remember...no L1011 has ever crashed due to an aircraft/engine design defect...quite unlike the B747 or the DC10.

Lockheed TriStar, simply a superior design...make no mistake.;)

Boarded a CRJ700 in Aspen, CO a few days ago. It was no warmer than -10C outside and that hair dryer of a APU was struggling to keep it colder than 30C in the cabin.

Ended up leaving 10 people behind due to weight restrictions.... They shoulda kept those BAe146's.....

Thanks for the update 411A, but I don't see how

can be claimed. In a B747-400, dispatching with 1 u/s engine generator does not restrict one to 400 miles from an airport

Much later design.
In addition, the L1011 can also be dispatched with one engine IDG inop, with minor restriction, so long as the APU is functional.

No question about it, which is why we see so many still in service, today...

Could the 747 Classic use the APU for electrics when airborne?

Did the Classic parallel the engine gennerators?

Did the L1011 parallel the engine generators?

some could.

yes.

what's an L1011?

Yes, together with the APU generator, if it was operating...all done completely automatically.
IE: no Flight Engineer input necessary.

One should remember that the L1011 was the first truly automatic jet airliner...others followed.;)
Refer to the thread on CATIIIC capability to see why it works so well.
Except, it appears for the RAF, who has continuing major difficulties.:E

As SLF, I flew from LHR to IAD on a BA 744 with an inop APU. It was not comfortable on the upper deck until they got the engines going. Took two huffers to blow start the thing. Had to divert from IAD to PHL and spent an hour at the gate at PHL, again with no APU before they got customs spun up and let us off. For being loyal BA passengers, we all received a complimentary hour's worth of sauna at each end of the flight.

I vote for the APU working even on the 744.

-Old Ag

Some can, but with altitude limits. Engine generators sync, but will not sync with the APU generators.

A poor design from the get go.;)
Having said this, the -400 model seems to be a vast improvement over the 'classic' design.

Gee, life before APUs must have been unimaginable . . . with the world's early jet airliners all "dead in the water" . . .DHC106, SE210, B707, DC8, CV880, CV990 . . .:{

That's the furthest thing from the truth I've heard in a while. Sentence by sentence: You can start the engines off Battery Power only, the aircraft can be refueled by manually opening the fueling valves in the wing (#1 and #3) and under the LE devices on the right wing (#2). Ground Air/Start Cart is needed though (GPU not required).

Unless Boeing went the several versions of the fueling valves and manifolds (which they didn't) the 727 can be refueled without even the battery being on. The only part you got right is that the 727 APU shouldn't be used in flight (it can't be started anyway, but can be left on accidentally after takeoff, and will flame out around 25000 feet), some operators had the T/O Warning horn attached to the APU in addition to the Flaps, Trim and Speedbrakes to prevent inadvertant takeoff with the APU on.

Bar none it's one of the best remote operations jets in the world.

That must be why they're still hard at work earning a living today. Go figure.

I noticed several responses to 411A's statement above. Some asked why the L-1011 need the APU for overwater flight: Will it does not.

The L-1011 MMEL has no such restriction.

411A's airline may have added it to their MEL, which is allowed. The airlines MEL can always be more restrictive (never less restrictive) that the MMEL.

Now that I got to thinking about it, in a pinch you could start a 727 without even the battery being on, that's right, no power at all. All you need is air (however this is a long drawn out procedure I've had explained to me by PFEs who flew in war zones). Realistically though, you could start without aircraft electrics but you would need ground electrics.

I guess we attended different school then. I attended Braniff Ailines' FE and type school.

I do agree with this.

However, dead APU, no air cart, no go. You land, start the APU, shut the engines down, APU fails, will not restart, no air.

How are you going to start the engines?

One more point we differ.

This happened to me twice, on both occasions the APU did not flame out at FL 250. The APU fire warning coming on and the the fire bell ringing was the first indication that the APU was still running.

Also on both occasions, there was a pilot/FE, not a professional FE riding side saddle.

By the way, I do have over 7,000 hours flying the 727.

I did say the only thing you need is air, so no APU=not dead in the water.

I've left it on once and noticed it at 1000 MSL and switched it off... I've heard leaving the APU on results in everything from it just flaming out to blowing up the tires to fire bells to compressor stalls (when switching onto #2 bleed in flight) etc. etc. I've never let it get that far and the most common one I hear is a flamout.

I'm not sure how much they taught you at EA, but I've had to climb under the LE flap more than once to override a premature VTO shutoff.

Actually in the FE school they taught that the first indication of the APU still being on after takeoff was the Wheel Well fire alarm would come on. So the first time this happened we all were concerned that even though the fire bell was ringing, none of the fire warning lights on the instrument panel were illuminated. Unfortunately my eager co-pilot silenced the bell just about as fast as the bell rang.

I remarked to the co-pilot that I kind of wished he had not done that, silence the bell, as we had an overheat/fire condition indicated somewhere. So trouble shooting was now rather limited. So I told him to recheck the lights, there was a chance that two bulbs had gone out at the same time, but not very likely. Just about then I started to think on just what could set off an fire alarm, but not light up anything on the instrument panel. Then it hit me, the APU.

So I kind of stood up in my seat, craned my head around so I could see the APU panel and sure enough, the APU fire light was on. So I told the FE to shut down the APU, so he grabed the start/stop switch and moved it to off. Of course the switch is disabled while airborne, so I had to tell him to pull the APU fire handle. He did and the light went out immediately.

Then he started arguing with me, he claimed that he did shut down the APU before takeoff and that the APU must have self-generated a start.

Besides being a terrible FE, he wasn't much of a pilot either as it turned out.

Give me a professional Flight Engineer any day.