Packs Off And/Or APU On For Takeoff

[AeroTech]

Hi,

-Is it common to use packs off and/or APU for takeoff and initial climb?

-It will be nice if someone can give a number for the paylaod gain when using packs off and/or APU for takeoff

-Wondering which thrust reverser (petals or cascades) provides less stopping distance?

-During normal or high speed RTO, if one engine fails or dispatched inoperative can the crew use the thrust reverser of other operating engine(s)?


Feedback appreciated
Regards

[TopBunk]

1. Becoming much more so

2. B747-400, + 2.0 tonnes with packs off, +1.9 tonnes packs APU to pack (lose 0.1 tonne due APU door drag)

3. pass

4. B747-400, yes but have to be prepared to cancel to control any swing then revert to symmetrical reverse thrust (ie if eng#1 failed, only use rev on #2 and #3)

[SNS3Guppy]

In the B742, we (the operator for whom I fly) performs all takeoffs with packs and APU off.

I have no idea about payload gain, but our practice is standard, even when empty.

[reivilo]

1. No, unless required for performance. It reduces passenger comfort (APU bleed air smells because it takes in engine exhaust air...)

2. In B738 gain is about 700-1300kg when taking off with engine bleeds off.

3. Don't know. Unless on wet runway, reverse thrust is not calculated in the accelerate stop distance.

4. Yes. Take care with crosswind and be prepared to reduce/cancel reverse thrust when directional control becomes difficult.

[Jinkster]

1) Working at a small airfield, with underpowered a/c - so happens quite alot (B733)

2) 800 to 1200kg gain

3) Not sure

4) Absolutely can use it. Also Single engine landing, reverser maybe used.

[Wizofoz]

I think petals are actually more effective, but are an engineering near-impossibility on a high-bypass turbo fan.

[cactusbusdrvr]

For all our types out of a short, noise sensitive airport like SNA (orange county, CA USA) we do a Bleeds off T/O. I forget the exact numbers but it is worth several thousand lbs of payload.

Also, we have A 320s with IAE 2500 A1 power (A5 is now the standard). Out of PHX and LAS in the summer with temps above 45 C we will do APU on (our airbus term now for engine bleeds off) T/O for payload and also EGT consideration. Engine bleeds off - lower EGT.

[ggofpac]

:Ofor a320, is the performance gained the same for packs off or packs on apu bleed take off?
thanks.

[mutt]

This is another one of your questions that depends on the aircraft/payload/airport........

1: Yes its done, although some aircraft have automated systems whereas if an engine fails the pack on the other engine/s will automatically shut off.

2: I've seen around 150 kgs on our small jets up to 6,000 KGS on a 772. (Many years ago, APU takeoffs weren't permitted in the 772 so it was PACKS ON or nothing, but that has since changed)

3: No idea.

4: Yes and if the takeoff was on a contaminated runway, you might find that the stopping distance is based on them using that other thrust reverser/s.

Mutt

[AeroTech]

Hi,

Thanks for your feedback.

2: I've seen around 150 kgs on our small jets up to 6,000 KGS on a 772. (Many years ago, APU takeoffs weren't permitted in the 772 so it was PACKS ON or nothing, but that has since changed)

Mutt, do you know why 772 APU takeoffs were not permitted at that time?

Regards.

[mutt]

We were told that it was due to disrupted airflow over the rudder due to the opened APU inlet.

Mutt

[con-pilot]

In the Falcon 50 and 900 the packs* are automatically turned off on takeoff and the APU is shut down after third engine start. So all takeoffs are packs and APU off.

* Actually, the bleed valves from the engines are shut automatically, then slowly reopened after takeoff.

[King on a Wing]

@SNS3Guppy....mate,u mean u did all take offs unpressurised? Wow,that must be unplesant for the pax no??
The petals or buckets positively provide lesser stopping distance by as much as 27% as against the cascades or sleeves,all other things remeining constant of course. Unfortunately I have not seen the buckets on any engines with a thrust rating greater than 20k....for obvious reasons. Noise emissions and enviormental emission standards(not even talking about economy) stipulate the use of higher and higher bypass ratios for bigger engines. Like someone rightly pointed out earlier,it would eventually be impossible to fit one of those larger diameter engines with the 'bucket type' reversers.So although they provide lesser stopping distance,they are unfortunately limited to smaller diameter engines with a low bypass ratio.
Hope that helped...the rest of your queries have been adequately adressed by the other forum members i presume.
Enjoy the gift of flight!

[DutchBird-757]

1. Standard practice for us when departing home base London City Airport on our E170/190's. APU shutdown before leaving stand and packs are automatically commanded off when t/o thrust is set. Imput by MCDU.

2. Couple hunderd kilo's.

3. Reversers are pretty useless for our operation. Just lot's of noise and vibration. SOP for us is to always use idle reverse and let the carbon brakes do the braking. Even at MLAW into LCY. They need to be replaced every x months so better wear them down as you're paying for it anyway. Obviously can/will be used whenever conditions require so. (RTO etc)

4. SOP is to use full reverse on BOTH engines during RTO, even with one on fire. Wether or not you would want to do it personally is another question but assurance by manufacturer that it's the better option.

[captjns]

For a "NO BLEEDS TAKEOFF" on the B737;

1. APU Bleed Valve open;
2. Engine Bleed Valves closed;
3. Isolation Valve Switch closed;
4. Pack Switches - Both On (The right pack receives no bleed air from engine number 2 as the bleed air valve is closed, nor air from the APU as the isolation valve is also closed.

Engine driven generators are powering their respective generator buses thus no issue there.

Company procedures vary as to reconfiguring the bleeds for normal operation after takeoff.

With the above said, every takeoff is a pressurized takeoff.

[AeroTech]

Hi,

Yes and if the takeoff was on a contaminated runway, you might find that the stopping distance is based on them using that other thrust reverser/s.

Mutt, if aircraft swings you have to reduce/cancel the thrust reverser (as mentioned above). I am wondering if this is considered for the stopping distance calculation, or it will not affect the stopping distance.


King on a Wing, if I am not mistaken petals reverser and buckets reverser are different. Petals reverser reverse the bypass airflow but the buckets reverser reverse the bypass airflow and the core engine exhaust gas (I am talking here in general may be there are some engines fitted…???)

You can see the pic (EasyJet aircraft, you can zoom it out) of the petals reverser in the following link:
Thrust reversal - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Thrust_reversal)

It seems to me that they may provide less stopping distance because the petals provide also drag; if so why they are not used a lot as the cascades thrust reverser?

Con-pilot, you mentioned takeoff bleed off with APU off. I am wondering if Falcon 50 & 900 are not fitted with hydraulic tank(s) pressurization (I am not familiar with these aircraft).

Finally it seems that there is packs off takeoff and bleed off takeoff.

Feedback appreciated.