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Full Power Take-Off Icy/Snowy Conditions  
User currently offline1400mph From United Kingdom, joined Jan 2013, 831 posts, RR: 0
Posted (1 year 7 months 12 hours ago) and read 2634 times:
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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.

 

7 replies: All unread, jump to last
 
User currently offlinetb727 From United States of America, joined Jun 2005, 1586 posts, RR: 9
Reply 1, posted (1 year 7 months 11 hours ago) and read 2550 times:

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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User currently offlineMir From United States of America, joined Jan 2004, 21552 posts, RR: 55
Reply 2, posted (1 year 7 months 11 hours ago) and read 2538 times:

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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User currently offlinemusang From United Kingdom, joined Apr 2001, 864 posts, RR: 7
Reply 3, posted (1 year 7 months 11 hours ago) and read 2524 times:

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


User currently offline113312 From United States of America, joined Apr 2005, 571 posts, RR: 1
Reply 4, posted (1 year 7 months 11 hours ago) and read 2516 times:

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.

User currently onlinevikkyvik From United States of America, joined Jul 2003, 9897 posts, RR: 26
Reply 5, posted (1 year 7 months 11 hours ago) and read 2496 times:
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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?



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlinemusang From United Kingdom, joined Apr 2001, 864 posts, RR: 7
Reply 6, posted (1 year 7 months 10 hours ago) and read 2478 times:

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


User currently offlineMir From United States of America, joined Jan 2004, 21552 posts, RR: 55
Reply 7, posted (1 year 7 months 9 hours ago) and read 2421 times:

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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