View Full Version : Assumed/flex Temp Effect On TORA And ASDA

7th Oct 2008, 00:39

The following is an excrept from HANDLING BIG JETS page 204,(a)
[ The assumed temperature method of reducing thrust to suit T/O weight does so at constant thrust/weight ratio and the actual T/O distance TORA and ASDA at reduced thrust are less than at full thrust and full weight by approximately 1% for every 3 degrees centigrade that the actual temperature is below the assumed temperature]

can this statement be validated,and if so,should this reduction/correction be applied or is it already accounted for in the runway analysis chart?


7th Oct 2008, 02:04
Generally, already applied in the runway analysis chart....at least the ones I have used, anyway.
A very deep derate (L1011-200, +50C) at nearly max weight, will use every bit of the 13,000 feet at JED (34L), for example, while still meeting the second segment climb requirement.
Up close and personal with the far end of the runway....:ooh:

7th Oct 2008, 05:06
Thanks 411A.....we too operate to and from JED, will try a high flex T/O from JED at the upcoming hadj season when we're fully loaded and then some
see if i can take all the adrenalin...:uhoh:

7th Oct 2008, 06:03
1% for every 3 degrees.... This will be airplane specific, but i remember that the Classic B747 is approx 1,500 kgs per degree, which certainly isnt 1%. Reduced thrust from Jeddah isnt a problem, especially in twins, but try it from Surabaya! Enjoy the Hajj.

On 411A L1011, a deep derate was limited to -25%, on modern Airbus this can be upto -40% depending on type/engine combination.


7th Oct 2008, 06:20
Remember that the quote comes from some time ago. Modern performance calcs/capabilities can muddy the picture.
Derate is available on the 777 300 er to 40% and assumed temps of 72 degrees C are not uncommon.
Also, the optimisation of V2 can change the picture, V1 being increased to "almost" balance the field and Vr increaseing to take advantage of any spare runway length, so increasing V2 and climb performance/wt available.
So a small change in the assumed can give a relatively large change in speeds or a change in optimum flap for the same wt/runway.

7th Oct 2008, 18:46
Hi guys........thanks a lot, the picture is clearer now
any idea on where to get the data for the A320-232 with IAE V2500 A-5 ?

7th Oct 2008, 21:36
Check the electronic AFM in PEP with the appropriate databases for your aircraft.


Old Smokey
10th Oct 2008, 12:24

A bit off topic, but having seen a few of "yours" using Surabaya, was wondering if you stuck to your normal procedure and used Balanced Field, or used SWY and CWY?

We don't from there, but we're not travelling anywhere near as far as you do.

Just wondering........


Old Smokey

10th Oct 2008, 15:26
OS, last time that i visited Surabaya, they had removed the clearway from their documentation, we therefore stopped using it, this resulted in a 4000 kgs reduction. We dont use the stopway. Luckily, the resulting takeoff weight is just enough to make it non-stop most of the time.