Assumed Temp & D-ATIS

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pilotito84
Posts: 59
Joined: Mon Sep 11, 2017 3:47 pm
Location: Tucson, AZ

Assumed Temp & D-ATIS

Post by pilotito84 »

Hello everyone,

I don't know if this has been posted/discussed before but I couldn't find any old posts regarding these two questions, so I'm just going to ask and if it has already been discussed please point me in the right direction.

How are you guys adjusting for assumed temperature on Sim-avionics? The reason I ask is because it seems I can never get more than 66 deg C. I have been using TOPCAT and TOPER 777 for my take-off calc. and they give me an assumed temp of +70 deg. with an N1 of 87.8%, and the best I can get is 65 deg with like 92% N1 on my CDU Perf page, which rockets the aircraft at 4000-6000 fpm rate of climb. In case anyone wants to try it, these are the parameters for the flight I did. B777-200ER from LFPG Rwy 27L Wind 250/5 OAT 23 QNH 1017 Flaps 5 TO Wgt: 459,829 lbs.

Second question: Is there a way to tune and get D-ATIS thru Sim-Avionics?

Francisco

thomas747400
Posts: 101
Joined: Sun Feb 14, 2016 12:37 am
Location: Perth, Western Australia

Re: Assumed Temp & D-ATIS

Post by thomas747400 »

Hi Francisco,

I have adjusted my default engine derate via the CDU > INIT REF > INDEX > AIRLINE POLICY

My settings are as follows:
TO & CLM DERATE 1 >15%
TO & CLM DERATE 2 > 30%

Most of my flights are quite short (GTOW 200-210t) and I almost always derate to TO2 - 65C (N1 > 80-84%). This allows me to have a long takeoff roll (around 2000m) and a manageable climb rate (usually around 3000 ft/min).

I am keen to know how Sim-A calculates N1 for a specific derate as results for a given setting is not always the same. I assume TGOW and/ or ambient conditions (temp/ density altitude) have an effect on the computation.

Thomas

pilotito84
Posts: 59
Joined: Mon Sep 11, 2017 3:47 pm
Location: Tucson, AZ

Re: Assumed Temp & D-ATIS

Post by pilotito84 »

Hello Thomas,

I might have to do the same thing you did. The numbers you mentioned sounds a lot better than my Boeing 777 taking off in around 3000 ft or 1000m of runway, and climbing at over 4000 fpm. The other option could be to modify the perf data file but I have no reference to what numbers I should use.

Francisco

pilotito84
Posts: 59
Joined: Mon Sep 11, 2017 3:47 pm
Location: Tucson, AZ

Re: Assumed Temp & D-ATIS

Post by pilotito84 »

Hello Thomas,

I de-rated the engines as you suggested, but it didn’t make much of a difference. Even when TO2 was selected with an assumed temp. Of 65 deg it only limits my N1 to 95.1%. For some reason i it seems that cant get it to derate below 92%. I tried the same settings: weight, fuel, weather, airport, etc on the CS777 and the fms did allowed me to type 70 deg as suggested by topcat and topper777 and de rated to 84% which i had to decrease my temperature to 61 deg to get it at 85.6% N1 for my takeoff. And this gave me a very manageable climb of around 2-3k fpm. So no i wonder what im doing wrong.

Francisco

pilotito84
Posts: 59
Joined: Mon Sep 11, 2017 3:47 pm
Location: Tucson, AZ

Re: Assumed Temp

Post by pilotito84 »

So I just did another flight from KATL to EIDW with the following parameters. ZFW 386400 lbs TGW 498397 lbs. The wx conditions were winds 350/10 temp 30 alt 30.15 rwy 09L and according to TOPCAT calculations it suggested D-TO1 with assumed temp of 62 and N1 92.8 Speeds of V1 146 Vr 147 and V2 150. I took all of this to the FMC and even with typing the max allowed temp of 66 deg I still couldn't get the N1 to get lower than 101.2%. It didn't matter if it was D-TO1 or 2 it just locked on 101%. so again a rocketed down the runway and climb at 5-6000 fpm.

Does anybody have any suggestions or ideas why I cannot get lower N1 settings??

Francisco

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