Sign in to follow this  
CPA156

Which Take Off Thrust Setting to Use and When?

Recommended Posts

Hey EveryoneI am struggling to choose what thrust setting to use on specific Take-Offs (on the 744). I want to De-Rate the thrust as much as I can, but when can I do this? How do I know if I don't use max thrust I won't get off the runway? Are there any tables out there referring to what distance is used during specific situations using different settings eg TO, T01 and TO2? thanksP.S. The only things I know are that in wet weather or if you have a tailwind you shouldn't de-rate.

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Hi there PatrickThe most common type of derate is an ASSUMED TEMPERATURE. As we all know, engine performance degrades on warmer days. Say the day is really 12 degrees ©, and we are okay to derate (ie no windshear, tailwind, MEL items, wet runway, no obstacles etc...). By looking up in tables by airport and runway, and finding your assumed weight (another whole process!), as most carriers do, one is able to find the maximum derate possilbe to use - which then usually used. This may be 48 degrees, just for example. They they then enter this number into the FMC (under ASSUMED TEMP), and upon takeoff, the computer will bring the engines to simulate the power you would get from them at full thrust on a 48 degree day, if you catch the meaning!TO1 and TO2 are "fixed derates" - which have their own set of limits and the such - probably best to check in the manual for a better explanation of these derates.I am pretty sure most carriers stick to simply assumed derates (I am free to be corrected here), and I know for certain that BA and QF only use assumed temps. Some, like SIA, I think, mix the derates up and use TO1 as well as an assumed temperature...Some companies (such as Lufthansa I think) have a laptop computer on the flight deck which calculates this and does all of the above (including calculating the assumed weight) and spits out the information you need to know - such as limit weights (climb, field etc), stopping distances, N1 values, and of course, the temperature. There are two such programs you can use to do this for the PMDG 747. One is an old one built for the PS1 744, which seems to work reasonably well with the PMDG 747, and will be able to tell you if a derate is available for the runway/airport/conditions/weight you are using, and calculates everything for you. I think it basically does pretty much everything the real one does. If you like, drop me an email at rudyfidao(at)iprimus.com.au (replace the (at) with @), and I can send it to you. You will, however, need MS Excel. The other is an absoultely fantastic one being developed by Mr Christian Grill - that is still in testing, but looks to absoultely fantastic!Also I think somewhere around, someone posted some real-world runway weight and assumed temp charts - could have been JonB I think. In the real world, every runway has a different table - there are no generic tables as such. Some of the airports I remember posted were VHHH, EGLL, KJKF, KLAX, KSFO, EWR...I hope you understand most of this, it may be a bit difficult sorry I am about to go to bed!Hope this helps, if you need any more help feel free to email/post or whatever!Rudy

Share this post


Link to post
Share on other sites

Thanks very much Rudy. So apart from those few De-Rate charts that Jon B gave out we have no other way of working out take-off thrust? I've seen Tomaflex except it doesn't wark with the 744. I have also seen a Excel sheet that works it out but I can't seem to open it. It wouldn't work properly because of a security issue with the macros or something. Anyone know anything about this? thanks

Share this post


Link to post
Share on other sites

Yep - easily fixed.Open Excel. Go to TOOLS > MACRO > SECURITY. Set the security to MEDIUM. Now Excel will ask you before it blocks the macros in the sheet, causing it not to work. When it asks (it will each time the sheet is opened), click ENABLE MACROS. Of course, be wary of sheets that you don't know about!Hope this helpsRudy

Share this post


Link to post
Share on other sites

RudyCan you link me to the file? I think i've deleted it and forgotten where to get it :(

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this