View Full Version : FLEX Temperature..

light chop
12th Jun 2001, 13:07
I would be grateful if someone could give me a definition of FLEX temperature a pilot has to enter the MCDU for takeoff parameters.

12th Jun 2001, 15:05
FLEX is an Airbus term for reduced thrust takeoff (flexible temperature).

During the takeoff phase FADEC calculates and commands a fixed takeoff thrust setting based upon an assumed temperature.

Quoting the Jeppesen A320 Airport Analysis manual

<font face="Verdana, Arial, Helvetica" size="2">Reduced Thrust Takeoff (Flexible Temperature)

Use of reduced thrust levels is optional but will ensure operating efficiency, reliability and engine service life. This "Flex" takeoff thrust is based upon an "Assumed temperature" (the maximum ambient temperature that will provide certificated takeoff performance for the given airport/runway and aircraft gross weight).

Flex Takeoff is not permitted when the runway is contaminated by standing water, slush, ice, or snow. Additionally, Flex takeoff is not recommended with tailwinds.

[list=1] Enter runway analysis with actual weight and wind. If actual weight is not shown, and interpolation is not desired, use the next highest weight shown in the analysis.
Read the maximum temperature shown in the box, or else interpolate
Apply temperature corrections shown in section iii as appropriate to determine the Corrected Temperature (CT). CT = maximum temperature + correction.
If CT is higher than OAT and TREF, use CT as flexible temperature, limit CT to ISA+45C.
If CT is below either OAT or TREF, the flexible takeoff is not allowed, and full takeoff thrust must be performed.
Takeoff speeds should be based on the flexible temperature (CT), and must exceed the minimum speeds computed for the actual OAT. If the minimum speeds exceed those shown at the flexible temperature, then a full thrust takeoff should be performed.[/list=a]</font>

The approach of how tailwind is used varies between operators, some allow FLEX takeoff with, some don’t, MEL items should be taken into account, the local weather (no wind shear), and crew judgment.

TREF is the engine flat rated temperature, A320 ISA+45C, A330 ISA+43C

Let me know if you would like to know what the corrections are for QNH, Anti-ice, and Bleeds are.

The Flying Lad
12th Jun 2001, 18:57
For which CFM56-5 variant is the A320 flat rated at 45C.

Secondly, what are the A340's CFM56-5-C4s flat rated at?



12th Jun 2001, 20:50

The Jepp airport analysis manual I was quoting from was for a A320-212 (CFM56-5A3, 26,500 lb takeoff thrust).


[This message has been edited by Zeke (edited 12 June 2001).]

13th Jun 2001, 01:03
For interests sake, Boeing calls 'flex', 'R-TO'. You might very well think that could cause confusion, but I couldn't possibly comment!

'Brighten my Northern Sky' Nick Drake R.I.P.

13th Jun 2001, 03:52
But boeing pilots call it a reduction.....


The Flying Lad
13th Jun 2001, 07:11
I thought Boeing pilots called it D-TO, or RN1.



13th Jun 2001, 11:49
We don't call it anything, as such, though we do speak of 'reducing'. The annunciation at the Thrust Mode Panel is R-TO, and this is what could be confusing.

My general point is that European manufacturers are better than Boeing at designing to avoid confusion at the human interface. I'm sure it's because they have put more thought into it.

Just pondering the consequences of a mis-understanding between crew members involving the spoken phrase 'rto' about the time of take-off..... Does it mean 'we need to stop', or 'the autobrake isn't set to RTO' or 'there's a problem with the thrust setting'? I'm getting into human frailty here, too, but it's a fact of life.

'Brighten my Northern Sky' Nick Drake R.I.P.

13th Jun 2001, 17:31
&gt;&gt;&gt;&gt;My general point is that European manufacturers are better than Boeing at designing to avoid confusion at the human interface. &lt;&lt;&lt;&lt;

Although I like to fly the A320, I still wonder at how many occasions the above stated is NOT true for Airbus. Why do You have to press the "wheels" button for the landing gear page on the systems display? Why is the pneumatic system sometimes called AIR, then BLEED?
And if You are looking for the Inertial Reference System, DON'T look in chapter "IRS" of the handbook, it's somewhere else.
I's a pleasure to fly, but some odd designs like the sunshade that comes lose if turned counterclockwise....

After all, it's a French car :-)

P.S.: but You also press the "START" button to shut off the Windows-PC, so aviation is not the only branch prone for possible confusion

[This message has been edited by maxmobil (edited 13 June 2001).]

13th Jun 2001, 23:55
It's funny, my boeing's thrust pannel says temp sel over the nob we use to select a reduced thrust setting and the EICAS screen says D-TO with a selected temperature. We simply call it a reduced thrust setting. :)

CCCCcc ough

14th Jun 2001, 10:19
Flying B727, and has done that for a couple of companies, never heard of anything but reduced or FLEX.


16th Jun 2001, 00:46
Im sorry airlift, did I speak?

CCCcccough, splutter and confused!

18th Jun 2001, 18:26
Hi Zeke. Wot a place to live, spent many happy months there. But I digress..

I note you quote the Jeppesen manual on A320 Airport Analysis, Flex Take-off procedures and am quite bothered by item 6. You quote that V speeds are based on the Flex Temp (Corrected Temperature). Are you sure this is correct?

I have always taught that the V speeds are based on Actual Take-Off Weight and make an association of Temperature & Power / Weight & Speed.

I work from the Airbus FCOM's and these indicate speeds are always based on ATOW, be it A320 or A340.

18th Jun 2001, 21:09
Sorry Cough for the confusion. My intent was to show that I was clearing my throat. I thought that's what you did to. Next time I'll read the names on the posts first.

P.S. you should do something about that cold if you cough so much.... :)

18th Jun 2001, 22:07
Hi all,

I am still confused about this flexing, assuming, reducing, derrating, ...

Zeke, you mentioned a correction factor on item 3 that you get from a table, what are they based on?

4pon4pin, I had the same view as you have about that the speeds calculations are based on the present conditions. But I had a look at the 737 Manuals and found that it is used ATOW and assumed temperature.

18th Jun 2001, 23:31

The logic is that if you can take off at the flex temperature and weight, you can takeoff at a weight less than that using the same V-speeds.


Dont compare Boeing takeoff policies with Airbus, they are totally different.


[This message has been edited by mutt (edited 18 June 2001).]

19th Jun 2001, 06:43
Flying lad: A-340s CFM 56-5-C4 are flat rated at ISA+15.

Zeke: I think that those numbers,A-320 ISA+45 and A-330 ISA+43, are T MAX and not T REF.
[For non Airbus Pilots,
T MAX:Maximum assumed (flex) Temperature.(ISA+40 in the 340.)
T REF:Flat Rating.]

19th Jun 2001, 11:09
Mutt is 100% correct with regard to the use of Boeing logic to Airbus performance, Boeing performance is based around the balanced field model, Airbus optimizes EVERYTHING. You cannot compare one to another.

Many people do not realize that the definition of V1, and takeoff performance has changed, the old school of thought does not apply. The Flight Safety Foundation published a comprehensive article on this subject, it is online here at FSF web site (PDF document) (http://www.flightsafety.org/fsd/fsd_oct98.pdf)

A summary of the article is as follows ....

<font face="Verdana, Arial, Helvetica" size="2">Recent revisions of the U.S. Federal Aviation Regulations and the European Joint Aviation Requirements redefine V1 as the maximum airspeed at which a flight crew must take the first action to safely reject a takeoff. Other revisions change the method of compensating for the time required by pilots to take action to reject a takeoff; require accelerate-stop data based on airplanes with fully worn brakes; and require wet-runway takeoff-performance data in airplane flight manuals.</font>


<font face="Verdana, Arial, Helvetica" size="2">Zeke, you mentioned a correction factor on item 3 that you get from a table, what are they based on?</font>

Quoting the same manual again (A320)

<font face="Verdana, Arial, Helvetica" size="2">Temperature Corrections for FLEX takeoff

When using Flex temperature takeoff (assumed temperature reduced thrust) the following temperature corrections are made to account for QNH and Bleeds

High QNH Add 1C per 0.30 Inch above 29.92 Inches (no correction when airport pressure altitude is 0 ft or below). Low QNH Subtract 1C per 0.10 Inch below 29.92 Inches. Engine Anti-ice on Subtract 1C. Total Anti-ice on Subtract 1C. Engine Bleeds on Subtract 3C.

Compare the corrected Flex Temperature (CT), the engine flat rated temperature (TREF), and the Outside Air Temperature (OAT. If CT is higher than both TREF and OAT, then take CT as the Flex Temperature, otherwise no flex temperature takoff is allowed. Note, the maximum flex temperature allowed is ISA+45C </font>


What you may be thinking of the corrections to the full thrust takeoff....I don't like the way this is worded, should replace every instance of weight with mass.

<font face="Verdana, Arial, Helvetica" size="2">Weight Corrections for Full Thrust Takeoff

When using full thrust performance the following temperature corrections are made to account for QNH and Bleeds

High QNH Add 100 kg per 0.10 Inch above 29.92 Inches (no correction when airport pressure altitude is 0 ft or below).. Low QNH Subtract 240 kg per 0.10 Inch below 29.92 Inches. Engine Anti-ice on Subtract 300 kg. Total Anti-ice on Subtract 800 kg. Engine Bleeds on Subtract 2000 kg.</font>


Did some digging...my little book here shows Tref of 30 and Tmax of 50

[This message has been edited by Zeke (edited 25 June 2001).]