B737 Wing anti ice with APU

[Olendirk]

Guys,

two short questions:

1. Why cant we use the bleed air of the apu for wingantiice?


2.How long can I use the overboost on the 737-300? is it time limitet?


Thanks!

OD

[Swedish Steve]

You can use APU bleed to supply wing antice, but there is not enough air and its not HOT enough so it wont do ant good.
Try selecting it on on the ground (On B737-300 onwards) or ground test on a -200, and watch the duct pressure drop. After about 20 secs you will see the duct pressure recover as the overtemp switches close the valves.

[Filip Bigün]

1:The APU isn´t sufficient enough to use it´s bleed air for WAI. Normally it supplies bleed air for one air conditioning pack either on the ground or in flight.

2: Dont know what you mean by overboost, but if it´s maximum takeoff thrust you mean, then you have a limitation of 5 minutes.

[Denti]

Or 10 minutes, depending on your ordered options. With the exception of two aircraft our whole fleet is certified for 10 minutes take off thrust. Should be in the limitations part of your FCOM, just check it.

[Filip Bigün]

Or 10 minutes, depending on your ordered options. With the exception of two aircraft our whole fleet is certified for 10 minutes take off thrust. Should be in the limitations part of your FCOM, just check it.

Which FCOM do you have? I have rev number 19 dated june 9 2006 and the limitation page number L.10.12 D6-27370-3Q8GJ-ILF June 4,2004. My company gave me new FCOM a month ago but maybe it wasnt the newest update? I certainly dont find any 10min max takeoff thrust, all i can find is 5 minutes.

[vapilot2004]

We have also used a 10 minute limitation on TOGA with some airplanes.

The 5 minute limit is reference maximum EGT.

[kotakota]

Thank God somebody can back me up after all these years . Back in 95 I was desperate ( but not too desperate ) for a long-term contract and applied to a certain Kingdoms airline for a place. The 'interview' was a farce , the 'Senior captain' who was to conduct the interview was 4 hours late , had hardly slept in 3 days , only his worry beads keeping him awake , and he asked the question about APU use in icing conditions. We embarked on an argument but you can never win against an interviewer who holds the pot.
Pathetic , why did he not ask me about flying in sandstorms ? I walked out and have blessed my Lucky Star ever since.

[relax.jet]

It depends on money. If you would pay for it Boeing can make magic and you are 10 minutes, if not you are 5 minutes. (the same is tailwind 10 vs 15 kts)

[Flight Detent]

Guys,

The 5 minute maximum thrust is designed for normal operations.

The 10 minute time limit is designed for engine out operations.

Cheers, FD :}

[atuk]

Q1..To avoid backpressure to apu bleed from eng bleed. Its boeing Non-AFM operational limitation that Apu bleed valve must be closed if eng bleed valve open. Wing anti ice bleed supply line is downstream of eng bleed air valve (same line as apu bleed line)

[Denti]

Guys,

The 5 minute maximum thrust is designed for normal operations.

The 10 minute time limit is designed for engine out operations.

Cheers, FD

Well, you can pay Boeing some extra and get 10 minutes take off thrust for both engines approved and certified. As usual it depends on what you are willing to dish out. Oh, and then there are those unfortunate planes that have only 5 minutes single engine take off thrust limit :(

[cfmoverboost]

If you refer to overboost as firewall thrust, then there is no time limit since you're exceeding the limits of the engine. 5 secs or 5 mins of firewall thrust will ground the airplane.

[Flight Detent]

Hi atuk -

your quote:

Q1..To avoid backpressure to apu bleed from eng bleed. Its boeing Non-AFM operational limitation that Apu bleed valve must be closed if eng bleed valve open.

is not quite correct:

If what you say is true, you wouldn't be able to start your engines with the APU bleed supply. I'm sure you meant to say that with both the engine and APU bleed valve open (DUAL BLEED light on), the respective engine must remain at idle.

Cheers, FD :rolleyes:

[atuk]

Yep...that's what i meant. Tks FD

[onehundred]

5 or 10 minutes T/O or G/A thrust?

It depends only on your national CAA.

FAA accepts only 5 minutes for engines used on planes registered N-abcdefg.
But FAA says also that if the company that builded the engine (PW, GE, ecc) certifies an engine in agreement with other nationals guidelines and CAA regulations, no problem. You can extend in emergency situations the use of T/O or G/A thrust up to 10 minutes, but you have to make a write up.

The reason for this is that you have T/O or G/A thrust 5 more minutes available in order to clear not close in obstacles and being this way not required to reduce your T/O weight (fuel or payload).

My airline has a mix of 737. Some certified for 5 minutes, other for 10 minutes.
But to set a standard we consider them all limited for 5 minutes.

Best regards

100

[Denti]

Aye, that seems to be the case. We had our fleet certified to 10 minutes to be able to fly into places like Innsbruck which is virtually impossible with 5 minutes limit (not that we've flown there in the past 8 years). However we took over two ex UAL and those are not only limited to only 20k lbs thrust rating but also to 5 minutes (and both were in a very poor state, we had to extend the take-over D check by 6 months to fix everything required).