Help with the Derrated Take-Offs

[Guest]

Hey!I have a problem while calculating the D-TO power setting I will be using for a specific T/O (Action performed by the CDU).I've checked the manual, and in the FMC Operations, I read that the temperature inputed into the CDU for a D-TO is between the actual OAT and 64

[Guest jase439]

I'm pretty certain the derates are accurate. Ian probably has a huge stash of tables on this. Keep in mind the '67 cruises at M0.82 at around 91-93% N1. Anyway, at ISA temps I was able to derate to 100.1% at 64C. The FMC in PIC will also let you derate up to 99C which will take you down all the way to 94.5% N1. Not sure if the real aircraft allows such high derates though.

[Guest Stratus_Fractus]

Are you inputting the temp under assumed temp or D-TO temp? I can get well over 80*C D-TO, thrust does depend slightly on assumed temp.HTH

[Guest Muppet22]

Hi guysBA has a maximum D-TO of 72 degrees C, I can't speak for other carriers.

[Guest jase439]

I wonder if these numbers are carrier specific or if they are based on hard performance specs given by the engine's manufacturer? While PIC will allow a derate of 99C, I would think that would be a rather dangerous proposition in most cases (obviously BA thinks so too ;-).Any of our resident 57/67 pilots know more on this?

[Guest]

Thanks for your answers, I guess the limit for American Airlines is 64

[Guest Matthias1975]

Okay, I have also read this in the manual but I still do not understand what the D-To temperature is. I thought I should use the outside temp??Can someone explain this to me please??Thank you!Matthias

[Guest]

Folks,When my "767 Dispatcher" Excel sheet http://ftp.avsim.com/dcforum/DCForumID33/1968.htmlis released no one will have to worry anymore about this. Just inform the conditions and the ASMD TMP will be printed on the TKOF card with expected reduced N1 for prompt use.And it works!Wagner

[Guest]

Hi Matthias,I'll give it a try. The purpose of de-rating is to reduce the performance of the engines to what is necessary. The more power an engine is asked to produce, the more wear and tear. To give you an example, Emirates are currently having problems with their RR Trent engines on the 777s, as they are nearly always asked to perform maximum thrust take-off's. Emirates claims that is part of the reason they are experiencing reduced reliability, and has had their ETOPS approval reduced from 180 to 120 minutes.By examining the route data, a de-rate can be calculated. The factors taken into account is take-off weight, runway lenght, runway contamination and the temperature. By consulting a range of charts the crew can calculate if a de-rate is possible, and by how much. The higher the de-rate temperature, the less power will be produced by the engines.Now all this rocket science can be a little deep without the proper manuals. I belive Wagner's tool will assist in the calculation, but if you really can't be bothered a de-rate of around 50C may be used. At MTOW from a hot and high airfield you may not want to de-rate at all, whereas on a cold day at sea level and at low weights, the de-rate will increase substantially. I normally de-rate anywhere between 45 and 55C, and usually get reasonable performance. 50C therefore is a good ball-park figure.But if you want to get it absolutely right, go with Wagner's tool.