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A320 takeoff thrust

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A320 takeoff thrust

Old 8th Feb 2023, 23:21
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A320 takeoff thrust

In headwind conditions, how fast would you say it is advisable to move the thrust levers to FLX detent after stabilization at 50percent?

Last edited by MD83FO; 8th Feb 2023 at 23:31.
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Old 9th Feb 2023, 05:25
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Originally Posted by MD83FO
In headwind conditions, how fast would you say it is advisable to move the thrust levers to FLX detent after stabilization at 50percent?
I don't think there's any guidance, just do it as fast as you like. Uneven acceleration is taken care of by the initial stabilisation then the FADEC will ensure the engines accelerate at an appropriate rate to take-off thrust. There is guidance for a strong crosswind, but that's not what you asked.
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Old 9th Feb 2023, 06:24
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Thrust levers just like everything else in Airbus are electrical switches. It just tells the FADEC to select appropriate acceleration schedule. So after the initial stabilization just move them in Flex detent. In a GA THR levers are just slammed to TOGA and FADEC gives the fastest acceleration schedule. It's similar.
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Old 9th Feb 2023, 06:29
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Originally Posted by vilas
Thrust levers just like everything else in Airbus are electrical switches. It just tells the FADEC to select appropriate acceleration schedule. So after the initial stabilization just move them in Flex detent. In a GA THR levers are just slammed to TOGA and FADEC gives the fastest acceleration schedule. It's similar.
I would argue that that is not exactly the complete picture, as the crosswind/tailwind procedure is markedly different for apparently a good reason. Especially when it comes to setting take off thrust.

That said, for a normal take off there is no guidance, so one could just slam them into the the FLX detent if one wishes, i would use a normal measured move though.
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Old 9th Feb 2023, 14:58
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Originally Posted by Denti
I would argue that that is not exactly the complete picture, as the crosswind/tailwind procedure is markedly different for apparently a good reason. Especially when it comes to setting take off thrust.

That said, for a normal take off there is no guidance, so one could just slam them into the the FLX detent if one wishes, i would use a normal measured move though.
The question asked is "In headwind conditions".
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Old 9th Feb 2023, 19:07
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Originally Posted by vilas
The question asked is "In headwind conditions".
Exactly - as far as the engine is concerned, a 'headwind' is goodness - it simply increases the airspeed that the inlet sees.
Crosswinds and tailwinds are a completely different story - the air having make that sharp turn around the inlet lip at lower airspeeds can result in inlet separation - which in turn will probably result in a fan stall/surge. Very unpleasant and potentially damaging and expensive. So caution must be exercised advancing the thrust levers for takeoff.
The center inlet on 727s was somewhat notorious for that - fortunately the JT8D was darn near bulletproof - surges rarely resulted in engine damage. Years ago I was flying out of Seattle on a 727. As we started the takeoff roll, the center engine surged - I was sitting near the front of the aircraft but it was still so loud I nearly jumped out of my seat. After getting over the initial shock from the big bang, my thought was "Oh - now I'll miss my connecting flight". But the pilot simply retarded the center engine thrust for a moment, then continued with the takeoff.
As I was getting off the aircraft in Salt Lake, I asked the pilot about it - he started into an explanation of what an engine surge was - I quickly stopped him, saying I was a propulsion engineer and understood all that - I was just surprised he continued the takeoff. He responded that if he'd aborted, they just would have gone back and tried again...
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Old 10th Feb 2023, 10:59
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Initially I couldn't believe that such a basic question was being asked and still not answered, but I always like to have documented references ready before I post, and to my surprise, I couldn't find one now. I'm surprised and humbled.

However, I very clearly remember in my days as a trainee, it was clearly explained (with FCTM references) that the levers must be moved slowly enough, so that actual N1 (green needle) closely follows the lever position (blue circle) on the EWD.

Safety First issue 27, has some useful info.

Anecdotally, I've had dodgy engines that from 50% (stabilised) to FLX had enough of differential thrust to require full rudder deflection. Surprisingly even after writing it up, the reply was that the acceleration on both engines was "within limits".
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Old 10th Feb 2023, 17:19
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On the Airbus a rapid advance of the thrust lever simply allows the engine to accelerate at it's FADEC schedule.

A slower advance of the thrust levers can allow a slower spoolup of the engines (if that is required) until the detent is reached.
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Old 10th Feb 2023, 18:25
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Originally Posted by J.L.Seagull
Initially I couldn't believe that such a basic question was being asked and still not answered, but I always like to have documented references ready before I post, and to my surprise, I couldn't find one now. I'm surprised and humbled.

However, I very clearly remember in my days as a trainee, it was clearly explained (with FCTM references) that the levers must be moved slowly enough, so that actual N1 (green needle) closely follows the lever position (blue circle) on the EWD.

Safety First issue 27, has some useful info.

Anecdotally, I've had dodgy engines that from 50% (stabilised) to FLX had enough of differential thrust to require full rudder deflection. Surprisingly even after writing it up, the reply was that the acceleration on both engines was "within limits".
Where those 'FADEC' engines? Because after a rapid thrust lever movement, FADEC accelerates (or decelerates) at a "N2 Dot" (or occasionally N1 Dot) schedule - i.e. the FADEC supplies the amount of fuel needed for the N2 (or N1) rotor to accelerate at the target speed. Coming off idle, there can be some other issues that come into play that can affect the engine accel rates (hence the 50% stabilized bit), but above that it would take an extremely unhealthy engine to not accel at the N2/N1 Dot schedule above 50% N1.
Pre-FADEC were governed differently - and various tolerances in the fuel control and engine to engine differences could dramatically affect the accel rates. FADEC pretty much did away with that - and unlike the 737 - the A320 never had non-FADEC engines.
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Old 11th Feb 2023, 03:32
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With no tail wind or crosswind less than 20kts it's a two step procedure, 50%N1 is the first step and for second step all it says set takeoff thrust. The procedure for tailwind or crosswind more than 20kt is different. It has three steps. First is same 50% N1, second step asks you to rapidly move thrust levers to 70% and third step ask for moving thrust levers progressively to takeoff thrust. So how the thrust levers are to be moved in the two scenarios is quite clear.
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Old 11th Feb 2023, 04:19
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Originally Posted by tdracer
Where those 'FADEC' engines? Because after a rapid thrust lever movement, FADEC accelerates (or decelerates) at a "N2 Dot" (or occasionally N1 Dot) schedule - i.e. the FADEC supplies the amount of fuel needed for the N2 (or N1) rotor to accelerate at the target speed. Coming off idle, there can be some other issues that come into play that can affect the engine accel rates (hence the 50% stabilized bit), but above that it would take an extremely unhealthy engine to not accel at the N2/N1 Dot schedule above 50% N1.
Pre-FADEC were governed differently - and various tolerances in the fuel control and engine to engine differences could dramatically affect the accel rates. FADEC pretty much did away with that - and unlike the 737 - the A320 never had non-FADEC engines.

​​​​​​Yes, regular CFM engines on the A320. The FADEC does what it needs to on its own engine. There's no differential thrust protection function that compares thrust between engines, so from time to time you do see one engine taking 2 or 3 seconds longer to spool up. Can be unnerving if caught off guard, esp for the inexperienced guys
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Old 11th Feb 2023, 08:38
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I've heard it said that some people set the stabilisation thrust (initially) by reference to markings next to the THR LVR quadrant.... any truth to that?

Originally Posted by vilas
With no tail wind or crosswind less than 20kts it's a two step procedure, 50%N1 is the first step and for second step all it says set takeoff thrust. The procedure for tailwind or crosswind more than 20kt is different. It has three steps. First is same 50% N1, second step asks you to rapidly move thrust levers to 70% and third step ask for moving thrust levers progressively to takeoff thrust. So how the thrust levers are to be moved in the two scenarios is quite clear.
That lookalike the CFM procedure. IAE is a bit different.
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Old 11th Feb 2023, 09:02
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Originally Posted by compressor stall
I've heard it said that some people set the stabilisation thrust (initially) by reference to markings next to the THR LVR quadrant.... any truth to that?
Bringing the thrust levers up to abeam the cross on the “T” in “A/THR” is pretty close to 50% N1 / 1.05 EPR and was mentioned in my endorsement but I just use the donuts on the N1 / EPR display.
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Old 11th Feb 2023, 10:10
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Originally Posted by compressor stall
I've heard it said that some people set the stabilisation thrust (initially) by reference to markings next to the THR LVR quadrant.... any truth to that?
I was taught that “trick”. Still do it on the IAE, as there’s no mark at 1.05. Not necessary on the CFM.
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Old 11th Feb 2023, 12:50
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Originally Posted by Check Airman
I was taught that “trick”. Still do it on the IAE, as there’s no mark at 1.05. Not necessary on the CFM.
Not to be rude guys, but forget all those “tricks” that some people including myself would call with another not-so-gentle word and just stick to the manufacturer’s/airline guidelines. :-)
Never flown the IAE, but as far as I remember from a sim session once, if you put the TLA halfway between 1 and 1.1 that’s your 1.05.
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Old 11th Feb 2023, 18:21
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Originally Posted by AerocatS2A
Bringing the thrust levers up to abeam the cross on the “T” in “A/THR” is pretty close to 50% N1 / 1.05 EPR and was mentioned in my endorsement but I just use the donuts on the N1 / EPR display.
Same, showed to do "H" from the instructor. WTF are the doughnuts for? Never used it since, happy years ensued.

There is a drill I ended up demonstrating recently, over and over again. The difference between a control / selector / input field and the resulting indicator.

Clearly, we move the selector and verify on the indicator, easily explained with the parking brake. Don't need to be completely picky (seat-belts SW) and for many items there is no indicator at all, but when available not using the indicators is just wrong. Flight control check with the double cross on PFD, NAVAID on MCDU, headings on FCU, ... geez.

This should be standard required skill, but it isn't.

Last edited by FlightDetent; 11th Feb 2023 at 18:33.
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Old 11th Feb 2023, 18:47
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For airplanes that don't have a lever command indicator on the gauges, a convenient marking on the quadrant is a great technique. For airplanes that do have one... why, just why?
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Old 11th Feb 2023, 19:05
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Originally Posted by sonicbum
Not to be rude guys, but forget all those “tricks” that some people including myself would call with another not-so-gentle word and just stick to the manufacturer’s/airline guidelines. :-)
Never flown the IAE, but as far as I remember from a sim session once, if you put the TLA halfway between 1 and 1.1 that’s your 1.05.
Yes, 1.05 is halfway between 1.0 and 1.1 (as you would expect).
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Old 11th Feb 2023, 19:15
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Originally Posted by sonicbum
Not to be rude guys, but forget all those “tricks” that some people including myself would call with another not-so-gentle word and just stick to the manufacturer’s/airline guidelines. :-)
Never flown the IAE, but as far as I remember from a sim session once, if you put the TLA halfway between 1 and 1.1 that’s your 1.05.
Get back in the sim, it goes 1 straight to 1.2, and that’s only a small part of the scale. Lot easier until you’ve got the muscle memory to set a visual picture than try and gauge 25% of the way of just a small scale graduation.

At least after a couple of hundred goes your hand just does it, surprisingly accurately as well.
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Old 11th Feb 2023, 19:29
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Originally Posted by J.L.Seagull
​​​​​​Yes, regular CFM engines on the A320. The FADEC does what it needs to on its own engine. There's no differential thrust protection function that compares thrust between engines, so from time to time you do see one engine taking 2 or 3 seconds longer to spool up. Can be unnerving if caught off guard, esp for the inexperienced guys
Seriously? You had CFM56-5 engines that took "2 or 3 seconds longer to spool up" from a stabilized 50% N1 to takeoff N1? IF that really happened, one of those engines was seriously sick. Plus, it would never pass the 8 second go-around accel requirement. Heck, it shouldn't take the engine much longer than "2 or 3 seconds" to spool up from 50% to Takeoff N1 - forget having that much engine-to-engine variation.
From ground idle? Sure - as noted small engine variations can cause them to run on different idle schedules - with varying off-idle acceleration characteristics. That's why the procedures tell you to advance the levers and stabilize prior to advancing to takeoff - if you don't do that (or don't do it properly) there can be big acceleration differences. RTOs are not uncommon due to asymmetric thrust and the resultant yaw overwhelming the ability to counteract with rudder/steering if the stabilization procedure isn't followed properly.
Used to occasionally get FDR data from asymmetric thrust caused RTOs - pilots always said they'd followed procedure and stabilized (IIRC, Boeing procedures call for 40% N1), but a simple look at the data would reveal that wasn't the case. Typically, they'd advance the levers to a midpoint on the quadrant - then go to takeoff when the first engine hit the target while the second engine lagged significantly.
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