1400mph
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Full Power Take-Off Icy/Snowy Conditions

Mon Jan 21, 2013 4:39 pm

Any pilots or aviation buffs outh there explain to me why I once was on an empty 747-400 (JFK - LHR) that did a full power take-off in snowy and icy conditions ?

Would just like to know why full power is standard procedure ?

Is it because the bird was very light.....

It was snowy and icy........

Combination of both ?

And what does this avoid / achieve ?

Thanks in advance.

 
 
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tb727
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RE: Full Power Take-Off Icy/Snowy Conditions

Mon Jan 21, 2013 5:19 pm

Given the conditions, you have to do a max thrust takeoff, at least at my company.

We may not do a reduced thrust takeoff if the a/c has been de-iced, with a contaminated runway or with the engine anti-ice on for takeoff. Maximum thrust power must be used.
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Mir
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RE: Full Power Take-Off Icy/Snowy Conditions

Mon Jan 21, 2013 5:24 pm

A contaminated runway means a full power takeoff at most companies (including mine).

Quoting 1400mph (Thread starter):
And what does this avoid / achieve ?

It gets the airplane off the runway faster, and thus makes the time where the plane can be affected by the slippery conditions shorter.

-Mir
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musang
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RE: Full Power Take-Off Icy/Snowy Conditions

Mon Jan 21, 2013 5:40 pm

Quoting Mir (Reply 2):
It gets the airplane off the runway faster

What Mir means is that it gets off the runway sooner, and in a shorter distance, and thus "...makes the time where etc etc..."

Another benefit is less exposure to contamination sticking to the aircraft (e.g. landing gear, brakes etc.)

In terms of airspeed it might well be slower than if a reduced thrust take-off was done. An increased take-off flap setting would reduce the rotate speed even more.

Regards - musang
 
113312
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RE: Full Power Take-Off Icy/Snowy Conditions

Mon Jan 21, 2013 6:00 pm

By accellerating faster, should the need arise to reject the takeoff, more distance will remain to stop. This is a big concern on a contaminated runway.
 
vikkyvik
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RE: Full Power Take-Off Icy/Snowy Conditions

Mon Jan 21, 2013 6:18 pm

Quoting musang (Reply 3):
In terms of airspeed it might well be slower than if a reduced thrust take-off was done.

All else equal, I would have thought that rotation would occur at the same IAS, no matter the thrust selected. Am I wrong?
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musang
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RE: Full Power Take-Off Icy/Snowy Conditions

Mon Jan 21, 2013 6:32 pm

I see where you're coming from, lower thrust = longer time to reach the same rotate/climb speeds, which would be true all things being equal. However.....

Reduced thrust take-offs are typically done (assuming a long enough runway) combined with higher speeds, in "Improved Climb" take-offs. The benefits include reduced engine wear, reduced noise, better climb rate, better climb gradient, reduced fuel burn. I guess the increased tyre wear is insignificant or outweighed by the benefits.

Given a long runway, for a typical load in a 737, a full power launch may use, say, 92% thrust (N1) with a Vr (rotate speed) of about 135 knots. Improved climb take-off in the same situation might use only 86% thrust with Vr and V2 (rotate and initial climb) speeds typically 15 knots higher.

Regards - musang
 
Mir
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RE: Full Power Take-Off Icy/Snowy Conditions

Mon Jan 21, 2013 7:44 pm

Quoting musang (Reply 3):
What Mir means is that it gets off the runway sooner

Correct.

Quoting musang (Reply 3):
An increased take-off flap setting would reduce the rotate speed even more.

Unfortunately, we're not allowed to take off with flaps extended if anti-ice fluid has been applied to the aircraft (which is a possibility if the runway is contaminated), so we can't take advantage of that.

-Mir
7 billion, one nation, imagination...it's a beautiful day

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