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Attn BMI Pilots

Old 12th Aug 2005, 19:59
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Attn BMI Pilots

Hi,

Can you settle a long running discussion point for me please?

I work for a GA operator and regularly end up flying BMI. None of our pilots (albeit 737 skippers and other assorted Bizjets amongst them) seem to be able to explain (at least not in any definate way!) why all BMI flights seem to enjoy a negative push over at around 1000' after take off (it may simply be a slight reduction in climb rate, but it always feels a little 'sporty' down the back (well, not too far down the back...)

I'm only a PPL so my knowledge of SOPs is fairly limited but is it simply that? Or is there some other reason that I(we)'ve not considered?

Many thanks!

Dai
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Old 12th Aug 2005, 20:16
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Hi Daifly,

On the Airbus 320 we reduce thrust and accelerate at 1500 aal. This usually means a reduction in thrust and pitch. If the nose is not pitched down smoothly it can feel a little 'negative' down the back. If the auto pilot is engaged by this point you should not be able to feel anything as the Airbus is a 1g aeroplane - very passenger friendly. This should apply to all Airbus operators, not just bmi.

bmimainline
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Old 12th Aug 2005, 22:47
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Excellent - thanks for the quick response.

Perhaps everyone's been handflying recently!

(Come to think of it, yes, I've had it on BA A320's too... - which probably explains why the BBJ pilots I know aren't sure!)

Cheers!
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Old 13th Aug 2005, 09:07
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It's the same on the 73, mate. It's more a matter of PANS-OPS and JARs, rather than an aircraft-related issue. I'm pretty sure they do the same on the BBJ; I just wonder why "they're not sure"
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Old 13th Aug 2005, 12:30
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I think what are feeling is the autopilot lowering the nose, some people have already engaged it by then and it is far more aggressive than you would be if hand flying. Don't know why it does it that way, it normally flies very smoothly.
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Old 13th Aug 2005, 13:46
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True.

I actually believe that the Autopilot is a little rough from time to time when "nosing over" before thrust reduction.

TCX also reduce at 1500' AAL.

Of course I never handle the aircraft roughly... I leave that treatment for my wife when I get home !
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Old 20th Aug 2005, 08:53
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A bit off the question but,

We are now "de-rating" our take-offs to the extent that T/O thrust may actually be LOWER than CLB thrust.... In this case you will feel a small "push" if anything...

/CP
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Old 20th Aug 2005, 09:11
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Am I not right in thinking that derated t/o thrust can never be less than climb thrust? It would seem a bit odd to add power at aa.
BA Airbus's use a standard aa of 1000'aal unless noise/perf restrictions dictate otherwise.
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Old 20th Aug 2005, 12:31
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CaptainProp

We are now "de-rating" our take-offs to the extent that T/O thrust may actually be LOWER than CLB thrust
Interesting comment , the Airbus 320 FCOM statement on this is below:

Thrust must not be reduced by more than 25 % of the full rated takeoff thrust.


The flexible takeoff EPR cannot be lower than the Max Climb EPR at the same flight conditions.

The FADEC takes the above two constraints into account to determine flexible EPR.

The above two constraints also limit the
maximum flexible temperature at ISA + 55
(70C at Sea Level).


The flexible takeoff thrust cannot be lower than the Max Continuous thrust used for the final takeoff flight path computation (at ISA + 40).


The flexible temperature cannot be lower than the flat rating temperature, TREF*, or the actual temperature (OAT).
I have been using "flex thrust" or "standard derate" for about 30 years now. All of the types I have flown have had a similar policy statement to the one above and have employed some method of ensuring that the takeoff was carried out with not less than climb thrust. If you think it through, there really is no advantage to taking off with a lower thrust setting than that with which you intend to climb.

What type do you operate and what does the equivalent paragraph in your manual say?

YS

Last edited by Yellow Sun; 20th Aug 2005 at 13:38.
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Old 29th Aug 2005, 14:51
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Yellow sun - You are 100% correct! Guess I was talking out of my a** there!
To be honest I was actually more or less quoting one of our trainers (!!) on this one... Have (and I guess knowing better now, never will!!) experienced this, just heard a trainer making a comment on the subject.
Manual states:
" Thrust must not be reduced by more than 25 % of the full rated takeoff thrust.
The flexible takeoff N1 cannot be lower than the Max climb N1 at the same flight conditions.

The FADEC takes the above two constraints into account to determine flexible N1."

Learn something new every day!

/CP
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Old 31st Aug 2005, 15:18
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All of the above may well be true but there is no doubt that with a max. flex of 78 on our 319's that the take-off power is LESS than the power the engines settle at once the flaps are retracted and you are climbing away. N1, EPR and Fuel flow all increase, seems pointless to me as you said but that's what happens.
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Old 31st Aug 2005, 15:52
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Yellow Sun & Max Angle are both correct !!

Airbus Fadec sets the calculated EPR @ 60 kt, and at that time the conditions are satisfied - the flexible takeoff N1 calculated will not be lower than the Max climb N1 at the same flight conditions (i.e. only at that point in time).

At THR reduction the inflight conditions are all totally different.....
i.e. temp, pressure, and aircraft speed.

The result is exactly as Max says, parameters including N1 often will increase, the sound you hear will be a rising engine note as thrust levers are moved to the CLB gate.


Moley.
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