1400mph From United Kingdom, joined Jan 2013, 223 posts, RR: 0 Posted (3 months 4 weeks 1 day 2 hours ago) and read 1729 times:
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 ?
tb727 From United States of America, joined Jun 2005, 1374 posts, RR: 4 Reply 1, posted (3 months 4 weeks 1 day 2 hours ago) and read 1645 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.
musang From United Kingdom, joined Apr 2001, 754 posts, RR: 7 Reply 3, posted (3 months 4 weeks 1 day 1 hour ago) and read 1619 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.
113312 From United States of America, joined Apr 2005, 536 posts, RR: 1 Reply 4, posted (3 months 4 weeks 1 day 1 hour ago) and read 1611 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.
musang From United Kingdom, joined Apr 2001, 754 posts, RR: 7 Reply 6, posted (3 months 4 weeks 1 day ago) and read 1573 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.
Mir From United States of America, joined Jan 2004, 19695 posts, RR: 56 Reply 7, posted (3 months 4 weeks 23 hours ago) and read 1516 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
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