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Pilots: De-rated Take-offs - How Low?  
User currently offlineSevenHeavy From United Kingdom, joined Mar 2004, 1169 posts, RR: 9
Posted (11 years 5 days 18 hours ago) and read 3846 times:


I guess this question is mainly directed at members with jet flying experience but I would obviusly appreciate comments from anyone who could offer input.

We all know that pilots/airlines use derated engine power settings when conditions permit. What is the minimum (n1/n2) setting that you would use or have used for takeoffs i.e. 92% n1 etc?. I know that the lighter the aircraft and the more runway available means more scope for derated takeoffs but are there any aircraft or company restrictions which dictate minimum settings?.

Once again thanks for all input.



So long 701, it was nice knowing you.
11 replies: All unread, jump to last
User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4291 posts, RR: 36
Reply 1, posted (11 years 5 days 18 hours ago) and read 3830 times:

The CRJ we typically will use a FLEX temp of around 48 C....minimum N1 for takeoff (which this usually gives) is 85% N1.

Chicks dig winglets.
User currently offlineWing From Turkey, joined Oct 2000, 1588 posts, RR: 23
Reply 2, posted (11 years 5 days 14 hours ago) and read 3761 times:

As we mostly fly medium range(around 3 1/2 hours flying )full house(mostly charter flights), my experience is mostly we use 24K derate or 26K + asumed temp thrust reduction.Which wil give you roughly around 95-98 % N1.

follow me on my facebook page" captain wing's journey log"
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 66
Reply 3, posted (11 years 5 days 9 hours ago) and read 3706 times:

Under US regulations thrust reductions exceeding 25% of takeoff thrust are not permitted. Most reductions are far less than this as the highest temperatures and the highest centrifugal loads are reached in the last two or three percent. It is just not necessary to make cutbacks that deep. Also should not see a reduced takeoff thrust that is going to be lower than normal climb thrust at accel height. In other words, the plane should not take off, climb to a thousand feet and then INCREASE power.

It is not always possible to discern how much actual thrust reduction was used by looking at the N1 used for takeoff power. I've seen an assumed temperature forty degees higher than actual yeild an N1 in the mid 90s.

Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineLuis777 From Mexico, joined Aug 2004, 89 posts, RR: 0
Reply 4, posted (11 years 5 days 8 hours ago) and read 3700 times:

Many operators use reduced thrust takeoff whenever performance limits and noise abatement procedures permit. Thrust reduction or derate lowers EGT and extends engine life.

The first method is Assumed Temperature Method (ATM), this method achieves a takeoff thrust less than the full rated takeoff thrust by using an assumed temperature that is higher than the actual temperature. The maximum thrust reduction authorized by most regulatory agencies is 25% below any certified rating, on the 767 PW4000 could be as low as 1.39 EPR and on 737NG as low as 89% N1. (GE and RR use N1 as reference and PW uses EPR)

The second method is fixed derate which uses a takeoff thrust less than full rated thrust for which complete and independent performance data are provided in the Airplane Flight Manual. Derated thrust is obtained by selection of fixed tkeoff derates from the Flight Management Computer (FMC). TO1/CLB1 provides a takeoff/climb limit reduced 3%N1 (approximately 10% thrust). TO2/CLB2 provides a takeoff/climb reduced by 6%N1 (approximately 20% thrust).

I hope this info could help you.



User currently offlineG4doc2004 From United States of America, joined Feb 2004, 123 posts, RR: 0
Reply 5, posted (11 years 5 days 8 hours ago) and read 3678 times:

Our G-IV with the RR Tay 611-8 engine uses EPR's calculated by the FMS. "Power for the Day" is the max EPR available for use, and is usually in the range of 1.72 to 1.74 depending on temp, etc. "Flex Power" is the de-rated EPR and is what we usually use more for the advantage of extending engine life and making mid-life and overhauls less costly. The de-rated EPR is around 1.53-1.54.

"Failure to prepare is preparing to fail"--Benjamin Franklin
User currently offlineSevenheavy From United Kingdom, joined Mar 2004, 1169 posts, RR: 9
Reply 6, posted (11 years 5 days 6 hours ago) and read 3650 times:

Thanks for all the responses- all great info and much appreciated.
I had no idea at GE and RR use N1 and PW use EPR for reference - I wonder why?

Thanks again.


So long 701, it was nice knowing you.
User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4291 posts, RR: 36
Reply 7, posted (11 years 5 days 6 hours ago) and read 3648 times:

SlamClick- an interesting tidbit about my little bird- whenever we flex, we actually DO increase power for climb thrust. You'll go from 85% to about 88-89% N1 when setting climb thrust. I always thought that was wierd- I guess that's the way the Canuck Jet works.

Chicks dig winglets.
User currently offlineLowrider From United States of America, joined Jun 2004, 3220 posts, RR: 9
Reply 8, posted (11 years 5 days 4 hours ago) and read 3620 times:

That must be a company specific thing. For flex thrust takeoffs, if the N1 setting is below the climb setting, we leave it there until 10,000, If it was good enough to get you to 1000, the next 8-9 should be easy.

Proud OOTSK member
User currently offlineAAR90 From United States of America, joined Jan 2000, 3531 posts, RR: 44
Reply 9, posted (11 years 5 days 3 hours ago) and read 3624 times:

The first method is Assumed Temperature Method (ATM)...
The second method is fixed derate...

AA B738 operations utilize BOTH. The lowest N1 I recall seeing was 78%...had to look over the numbers more than twice, but everything matched up and that's what we used. Most often we'll be operating in the low 80% N1 range though.

*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlinePhilsquares From , joined Dec 1969, posts, RR:
Reply 10, posted (11 years 5 days 1 hour ago) and read 3571 times:

On the 744 you can and do use both methods. For example, at SQ, we ust TO-1 and assumed up to 52C. I know of other carriers who start at TO-2 and 52C.

To make a correction in Luis777's post, RR use EPR not N1. Only GE uses N1, PW, RR, IAE all use EPR.

User currently offlineRendezvous From New Zealand, joined May 2001, 528 posts, RR: 0
Reply 11, posted (11 years 5 days 1 hour ago) and read 3571 times:

You should see the Emirates 777-300s leave Auckland. They go trans-Tasman so flights are 3-4 hours. They use as much runway as a fully loaded 747-400 going to Los Angeles.

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