What is FLEX TEMPERATURE? Explained by “Captain” Joe

, , 100 Comments


Dear friends and followers today I’ll be answering another great question which was sent in by one of my YouTube subscribers Joe I’ve heard pilots talking about Flex temperature what’s that? That’s a great question so let’s get started Okay first off the Flex temperature is always referred to the takeoff performance setup for many jet powered airplanes except for Boeing They called it the assumed or derated temperature Okay in my example we will refer to an Airbus A320 with CFM turbofan jet engines Now many passengers have the impression that pilots always apply full power when performing a takeoff But do you remember the last time you sat in an Airbus that shortly after takeoff the engine sound decreased a little bit as if the power would drop Well that’s due to the Flex temperature and the climb power setting So prior to every takeoff you have to perform the takeoff calculations taking many factors into account First and foremost the aircraft takeoff weight The ramp agent will hand you a load sheet showing all the important figures you need for the calculations including the stabilizer trim setting and then you check the local ATIS and start filling up the module So let’s go with this example We have the takeoff weight of 68 tons and these environmental factors Once the calculation is finished you’ll get this data So what’s all this? You have the V1, the Vr and the V2 Those are the speeds in the next topic for the next video and the Flex temperature Now let’s use the suggested flex temperature of 58 degrees So you type in 58 degrees on your performance page and now the FADEC, the Full Authority Digital Engine Control unit assumes that the outside air temperature is 58 degrees and therefore the FADEC reduces the power purposely to reduce the engine wear in such “expected” hot temperatures So when applying the thrust levers to the Flex detent the FADEC will give you a 85.3% takeoff power setting Although you know there’s some extra power left which you can always access by applying TOGA at one further detent on the thrust lever column giving you maximum thrust available The result of using a high Flex temperature is that the speeds are higher for liftoff because the plane won’t accelerate as quickly as it could and therefore using up more runway resulting in a shorter stop distance in case of rejected takeoff So the conclusion of that is the lower the Flex temperature so the fake outside air temperature for the FADEC the more power will be set when applying thrust So the closer it is to TOGA The higher the Flex temperature the more the engines are derated resulting in a longer takeoff roll with higher speeds and at the same time reducing the engine wear So how can you as a passenger hear or feel the difference which Flex temperature was chosen? The best example is Lanzarote airport the airplane is close to the maximum takeoff weight on a very short runway therefore the plane needs a lot of power to accelerate as quickly as possible to reach the rotation speed The engine will literally roar much louder and after liftoff and reaching the thrust reduction altitude There’s a reason why they’ve named it the thrust reduction altitude where you set the takeoff thrust to climb thrust and you’ll hear and feel the power change a reduction in noise and deceleration in the climb rate But why do that in the first place? Why not just set TOGA thrust for every takeoff and go through all that hassle First and most importantly is to increase the engine life therefore reducing the chance of an engine problem due to technical failure more controllability of the aircraft with lower thrust output in case of an engine failure on the runway and just after liftoff and obviously the fuel flow is lower using a Flex temperature To sum up you would say the Flex temperature is the sweet balance between the stop margin available on the runway and a longer engine life and fuel economy But there are cases where the use of Flex temperature is prohibited in case the runway is contaminated with standing water or slush, snow or ice or whatever if the runway is very short at high altitudes and hot outside air temperature or performance reasons due to obstacle clearance in the departure sector the takeoff module will then calculate a TOGA thrust setting for you Now maybe you’ve experienced this you’re sitting at Boeing and as you gently lift up into the air and once you’ve reached your thrust reduction altitude suddenly more power is applied what’s going on? Some takeoffs on the Boeing, the thrust for the takeoff is reduced even below the climb thrust so let’s say, derated power is 75% and the climb power is at 85% You can feel and hear the increase of those 10% in power at the first reduction altitude and therefore thank you very much for your time please subscribe to my channel and check out my instagram account by the name @flywithcaptainjoe and spread the word. See you next week All the best
your Captain Joe

 

100 Responses

  1. Luke Mills

    August 8, 2018 9:53 am

    I was in an a330 and I felt it falling slightly during climb. do you know why the pilots did this?

    Reply
  2. ASHUTOSH NARAYAN SHARMA

    August 8, 2018 10:28 am

    Hallo Joe, Ich komme aus Indien. Ich lerne Deutsch, weil es ein interessante sprache ist. Die Video ist sehr interessant. Ich will nach Deutschland fliegen zu studieren.

    Reply
  3. Gabriel Santos

    August 13, 2018 11:54 pm

    What is your ICAO level, if I may ask, Captain? Because your English is almost perfect, congratulations. I know your mother is British by the way.

    Reply
  4. Joseph Quattrocchi

    August 19, 2018 3:43 am

    Captain Joe have you explained how air conditioning is achieved in an aircraft ? I am a HVAC technician and am sure planes have a creative way to cool the passengers.

    Reply
  5. academy.jccbi.gov.catalogue

    August 20, 2018 8:21 pm

    FAGO OR FLEX TEMPATURE COMPARED TO ALTITUDE AND IS ONLY FOUND IN THE CAPTIN'S AIRCRAFT. THE MODULE ONLY GIVES THE AIRMEN THE THROTTLE. AVS-I: THE ATN TELLS YOU.

    Reply
  6. academy.jccbi.gov.catalogue

    August 20, 2018 8:43 pm

    YOU MUST HAVE M OR THRUST POWER THAN FAGO NO MATTER WHAT KIND OF AIRCRAFT IT IS?

    Reply
  7. academy.jccbi.gov.catalogue

    August 20, 2018 9:22 pm

    DID YOU KNOW WHAT THEY DID IN THESE CITIES TODAY-PIXIE STICK, RIGHT TO LIFE. PREVIOUSLY, PARKED CARS?

    Reply
  8. academy.jccbi.gov.catalogue

    August 20, 2018 9:33 pm

    WELL THEN SMARTO LISTENER – IT IS A SPEED OF MPH or knots NOW LET'S SEE AN COMMERCIAL AIRCRAFT HAS A 15,000 FOOT RUNWAY? NOW THERE IS AN ADVISORY IN A FSMIS CHANGES VOLUMES?

    Reply
  9. academy.jccbi.gov.catalogue

    August 23, 2018 1:43 pm

    I WORK THE AIRLINE AIRPORT CERTIFICATION-FOR NOW? EVER HEARD OF AN ADVISORY OF A DERIDED TAKEOFF, MAYBE AC 25-13

    Reply
  10. academy.jccbi.gov.catalogue

    August 23, 2018 1:52 pm

    MAYBE THE WINGS HAVE FUEL IN TEN THE V-WING DESIGN AND THE AIRBUS DOES THAT AT TAKEOFF. THE WINGS HAVE TO BE STRAIGHT? GOTTA ATTORNEY?

    Reply
  11. Joe pragash

    August 28, 2018 2:31 pm

    Hello Captain Joe,This is Joe..I never Miss to Watch your Lessons, Your Explanations About the Questions Are Really Awesome and You are a Kinda Cool Captain…And I have a Question that I don't whether you have Answered Already or Not…!!Can you please Explain that "How Does Airplane Fly?"

    Reply
  12. Charles Magrin

    August 31, 2018 8:22 am

    nice video great explanations! "Captain"? you only have three stripes on your shoulders XD! just kidding hey 🙂

    Reply
  13. Julio Manoel

    September 7, 2018 3:18 am

    Hello captain! I am Julio from Brazil. Please, give us a new video explaining noise abatement procedures. Thank you!

    Reply
  14. javier al

    September 14, 2018 8:33 pm

    Hi Captain Joe. I have a question: Landing lights should be turned off above 10.000 ASL or AGL? Thanks in advance for your answer! Btw, your advice and explanations are great! Thanks for sharing your knowledge with us, simmers!

    Reply
  15. Hieronymuss Official - jeroen de Moor

    September 25, 2018 9:15 am

    Nice explain. I was always setting random crap in my CDU of my airbus and taking off on Man TOGA. meh.. thats why im not a reallife pilot i guess

    Reply
  16. turboV

    October 3, 2018 3:11 am

    How did you know Boeings reduce their De-rated T/O power below their climbpower, since you fly/flew Airbus? (assuming I understood correctly) kind regards 🙂

    Reply
  17. Andy Richards

    October 8, 2018 10:00 am

    Thank you for that, showing my age here, but I had always assumed the throttling back was due to noise abatement regulations.

    Reply
  18. Mark Goulet

    October 29, 2018 2:34 pm

    Why would Boeing pilots ever derate thrust below the climb thrust? And why then would climb thrust be higher in the first place? How does having a lower takeoff thrust than a climb thrust be beneficial to engine life? Is it noise related?

    Reply
  19. Nasser Faouri

    November 22, 2018 9:54 am

    Higher flex temp actually burns more fuel as it prolongs the takeoff segment. It’s in the FCTM green operating procedures… don’t mean to nit pick awesome videos

    Reply
  20. NeverTurnOffTheAmp

    December 9, 2018 1:22 pm

    I find it very surprising that obviously Vr has such a great margin that is not due aerodynamics but to available runway length for a rejected T/O. I always thought Vr would the earliest speed where it's safe to lift off, without too much of an speed-addition to reduce tire wear.

    Reply
  21. rambo romboni

    December 12, 2018 10:30 pm

    Hi Joe, i'm a bit confused as to why a slower acceleration would result in higher V speeds. Is it to do with balanced field length or am i way off? 🙂

    Reply
  22. Fobios TG

    December 13, 2018 11:49 am

    Your video did not made it instantly clear to me, what a flex temperature is. I assume following, high flex temperature means we have favorable take-off conditions like: head wind, high air pressure, cold air temperature – etc everything that increases jet engine thrust at a given RPM, coupled with the longer runway and light load resulting a lower thrust setting required for safe take off.
    Higher v1 in higher flex temperature, means that the plane moves slower on runway, thus pilots have more time to react. And flex Vr is higher from Vr (TOGA), because as the plane gathers momentum slower thus too early rotation (rotating at 140 kts for F58 setting) would result in instant stall condition on increasing the angle of attack?

    Reply
  23. James Strange

    January 8, 2019 11:19 pm

    Hi Capt. Joe…Thanks for the consistently clear, engaging and often humorous presentations of aviation topics. I wonder if you would be willing to do a series on emergency procedures for pilots. These could be by cause (e.g. engine out, etc) or by circumstance (e.g. reject takeoff, etc.). Thanks again for the great vids!!!

    Reply
  24. Rune Raad

    January 16, 2019 8:44 am

    IF you have a FADEC system….. Do you realy do those pre-take of calculations then? Thougt that was a procedure for older systems????? Cpt. Joe???

    Reply
  25. pic18f452

    February 5, 2019 3:41 am

    Hi captain Joe, wonderful stuff, it reminded me about the Saudi 747 in India that landed in a military airport and had to do a very short take off. Can you talk about that case please?

    Reply
  26. D A

    February 5, 2019 9:14 pm

    The missing point is that the FADEC will match the air density. When T is high the air density is low so for the FADEC no needs to waste fuel. That's the basic concept of flex Temp.

    Reply
  27. haider iqbal

    March 6, 2019 4:39 pm

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    Reply
  28. IFTIKHAR AHMED

    April 22, 2019 6:35 pm

    Hi Captain Joe , What is EGT , Thrust and N2 margin .How temperature variation effect on these . Plz explain briefly.

    Reply
  29. GAMINGdayzz

    June 8, 2019 10:35 pm

    Congrats on 1 mill,, 👍✈️✈️✈️✈️✈️🛩️🛩️🛩️🛩️🛫🛫🛫🛫🛬💺🛸🛬🛬🛬

    Reply
  30. Dr. Darren Martin PhD

    June 19, 2019 3:06 pm

    @1:10…When I work for the Airlines many years ago the weight of the cargo/luggage/passengers was always a guesstimate.

    Reply
  31. C-130 Hercules

    June 29, 2019 3:28 am

    What kind of person flex a temperature???

    John:Hey its hot here in the philippines

    Harold:Haha! here in Canada its really cold!

    Reply
  32. souhayb chaabi

    July 9, 2019 11:41 am

    Thank you, for this explanation, every time I am getting this warning "OUTER TK HI TEMP" is some flights, with accompanying suggestions on how to deal with it . I observe that both outer tanks are at high temperature. can you explain how do with it

    Reply
  33. احمد يعقوب

    September 3, 2019 11:04 am

    جو…رجاءا ترجم الفديوهات الى اللغة العربية بالسرعة الممكنه ليتسنى لنا متابعتها والاستفادة منها

    Reply
  34. Vasco da Gama

    October 15, 2019 6:58 pm

    but as the OAT increases you need more power for take off, so how come this fake increased flex temp leaves us with degraded power settings?

    Reply
  35. Riyas bin yousuf

    February 22, 2020 6:14 am

    Joe ..Pls explain how to determine N1 Limit for take off In Boeing 737-800. 22k/24k/26k. I think it depends on the weight and runway length. However I am looking forward ur help

    Reply

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