PPRuNe Forums

Go Back   PPRuNe Forums > Flight Deck Forums > Tech Log
Forgotten your Username/Password?

Tech Log The very best in practical technical discussion on the web


Closed Thread
 
Thread Tools
Old 12th Jun 2001, 12:07   #1 (permalink)
light chop
Guest
 
Posts: n/a
Question FLEX Temperature..

I would be grateful if someone could give me a definition of FLEX temperature a pilot has to enter the MCDU for takeoff parameters.
 
Old 12th Jun 2001, 14:05   #2 (permalink)
Zeke
Guest
 
Posts: n/a
Thumbs up

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

Quote:
<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.
 
Old 12th Jun 2001, 17:57   #3 (permalink)
The Flying Lad
Guest
 
Posts: n/a
Post

For which CFM56-5 variant is the A320 flat rated at 45C.

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

Cheers,

Justin
 
Old 12th Jun 2001, 19:50   #4 (permalink)
Zeke
Guest
 
Posts: n/a
Unhappy

Justin,

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).]
 
Old 13th Jun 2001, 00:03   #5 (permalink)
NorthernSky
Guest
 
Posts: n/a
Red face

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.
 
Old 13th Jun 2001, 02:52   #6 (permalink)
Cough
Guest
 
Posts: n/a
Wink

But boeing pilots call it a reduction.....

CCcccccccc.....ough
 
Old 13th Jun 2001, 06:11   #7 (permalink)
The Flying Lad
Guest
 
Posts: n/a
Post

I thought Boeing pilots called it D-TO, or RN1.

Cheers,

Justin
 
Old 13th Jun 2001, 10:49   #8 (permalink)
NorthernSky
Guest
 
Posts: n/a
Smile

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.
 
Old 13th Jun 2001, 16:31   #9 (permalink)
maxmobil
Guest
 
Posts: n/a
Post

&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).]
 
Old 13th Jun 2001, 22:55   #10 (permalink)
AIRLIFT
Guest
 
Posts: n/a
Wink

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
 
Old 14th Jun 2001, 09:19   #11 (permalink)
seupp
Guest
 
Posts: n/a
Post

Flying B727, and has done that for a couple of companies, never heard of anything but reduced or FLEX.

seupp
 
Old 15th Jun 2001, 23:46   #12 (permalink)
Cough
Guest
 
Posts: n/a
Post

Im sorry airlift, did I speak?

CCCcccough, splutter and confused!
 
Old 18th Jun 2001, 17:26   #13 (permalink)
4PON4PIN
Guest
 
Posts: n/a
Post

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.
 
Old 18th Jun 2001, 20:09   #14 (permalink)
AIRLIFT
Guest
 
Posts: n/a
Talking

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....
 
Old 18th Jun 2001, 21:07   #15 (permalink)
 
Join Date: Oct 1999
Location: luxembourg
Posts: 46
Post

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.

fernando is offline  
Old 18th Jun 2001, 22:31   #16 (permalink)
mutt
Guest
 
Posts: n/a
Post

4PON4PIN,

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.

Fernando,

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

Mutt


[This message has been edited by mutt (edited 18 June 2001).]
 
Old 19th Jun 2001, 05:43   #17 (permalink)
rodelu
Guest
 
Posts: n/a
Cool

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.]


 
Old 19th Jun 2001, 10:09   #18 (permalink)
Zeke
Guest
 
Posts: n/a
Unhappy

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)

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

Quote:
<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>
fernando

Quote:
<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)

Quote:
<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>
4PON4PIN

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.

Quote:
<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>
rodelu

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).]
 
Closed Thread
 
 
 


Thread Tools


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT. The time now is 01:34.


vBulletin® v3.8.7, Copyright ©2000-2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
1996-2012 The Professional Pilots Rumour Network