I have noticed that the A380-341 & 342 series equipped with rolls royce powerplants have a second spool up during takeoff approx 10 seconds into the takeoff. The throttle is already placed at approx 75-80% for the first several seconds, followed by another increase in throttle to approx 90-100% (TOGA). One example of this is the last China southern A380 Takeoff at LAX

https://youtu.be/33XTBzj2OGY

at 6:01:39 you can hear the second spool up, while the throttle was noticeably high earlier.

This also happened on my A380 flight from DXB-JFK on an Emirates A380-342. I have only noticed this on the A380 series, as there aren't really such changes in throttle during the takeoff roll on other wide-body aircraft. Can anyone shed light on this procedure or if it is standard practice?

It seems to me as if the PF is just taking a bit longer than usual to go to FLX or TOGA from the first intermediate setting.

For takeoff, you set the thrust levers to an intermediate setting (e.g. 1.1EPR on the A330 and 25% on the A350), then wait a second or so in order for the thrust to stabilise. Only then do you set the desired takeoff setting (FLX or TOGA). You want the thrust to stabilise because if you go all the way from idle to FLX or TOGA and the engines spool up with a significant asymmetry (or an engine fails), the resultant yaw moment might can give, to quote the manual, "directional control difficulties", perhaps even so much that you go off the side of the runway.

This is not unique to the A380, but again, I think the PF was just pausing a bit longer than usual.

Notes:
- Civilian jets have thrust levers, not throttles.
- The initial setting is more like 25% than 75-80%. Yes, it makes that much noise.
- TOGA is rarely used. Most likely a flex (assumed temperature) takeoff.

I'll add that with a tailwind or crossind above 20 knots, the A350 thrust setting procedure is bit more involved.

- Initially move the thrust levers from idle to the position that gives 25% thrust*.
- Once thrust is stabilised, progressively move the thrust levers to reach the following:
--- At 20 knots ground speed, thrust levers at CL (Climb detent).
--- At 40 knots ground speed, thrust levers at FLX or TOGA (Flex or TOGA detents).

Thrust is set in "steps" to mitigate flow disturbances in case of tailwind. It seems plausible that the A380 procedure is similar. Was there a tailwind or significant crosswind on the day of the video?

* The A350 has a synthetic linear thrust indication (as well as N1).

The Trent 900s on the A380 have an area of the thrust curve that cannot be exceeded when aircraft speed is too low. Depending on the take-off thrust setting, this often results in two 'pauses' during spool up. The first is the pilots stabilising all 4 engines at ~30% thrust, the second pause is the FADEC protecting the engines by limiting thrust until sufficient speed is reached, before finally spooling up to the commanded thrust.

FiftyLitres wrote:

The Trent 900s on the A380 have an area of the thrust curve that cannot be exceeded when aircraft speed is too low. Depending on the take-off thrust setting, this often results in two 'pauses' during spool up. The first is the pilots stabilising all 4 engines at ~30% thrust, the second pause is the FADEC protecting the engines by limiting thrust until sufficient speed is reached, before finally spooling up to the commanded thrust.

Good info, thanks!

The A330 Trents hav e the same feature, known in that case as MEASTO, Modified Engine Acceleration Schedule for TakeOff.

Starlionblue wrote:

FiftyLitres wrote:

The Trent 900s on the A380 have an area of the thrust curve that cannot be exceeded when aircraft speed is too low. Depending on the take-off thrust setting, this often results in two 'pauses' during spool up. The first is the pilots stabilising all 4 engines at ~30% thrust, the second pause is the FADEC protecting the engines by limiting thrust until sufficient speed is reached, before finally spooling up to the commanded thrust.

Good info, thanks!

The A330 Trents hav e the same feature, known in that case as MEASTO, Modified Engine Acceleration Schedule for TakeOff.

Imagine having to do all of this back in the steam gauge days. No wonder they needed a FE.

77west wrote:

Starlionblue wrote:

FiftyLitres wrote:

The Trent 900s on the A380 have an area of the thrust curve that cannot be exceeded when aircraft speed is too low. Depending on the take-off thrust setting, this often results in two 'pauses' during spool up. The first is the pilots stabilising all 4 engines at ~30% thrust, the second pause is the FADEC protecting the engines by limiting thrust until sufficient speed is reached, before finally spooling up to the commanded thrust.

Good info, thanks!

The A330 Trents hav e the same feature, known in that case as MEASTO, Modified Engine Acceleration Schedule for TakeOff.

Imagine having to do all of this back in the steam gauge days. No wonder they needed a FE.

Indeed. No wonder FADEC was the first widespread "control by wire" piece of kit in airliners. It really is akin to magic. The tolerances are insanely small if you think about it, and yet the engines take all that atmospheric conditions and hamfisted pilots throw at them without so much as a hiccup.

FADEC pucker factor #1.....During OEM ground run of the installed power plant,,,,Place a TL against the Max Noise stop and watch the gouges wind up so fast an exceedence appears to be assured, but all the needles stop decimal points shy of redline, all at the same time, with no hunting......Wow....hard to watch and not pull it back a bit.

77west wrote:

Starlionblue wrote:

FiftyLitres wrote:

The Trent 900s on the A380 have an area of the thrust curve that cannot be exceeded when aircraft speed is too low. Depending on the take-off thrust setting, this often results in two 'pauses' during spool up. The first is the pilots stabilising all 4 engines at ~30% thrust, the second pause is the FADEC protecting the engines by limiting thrust until sufficient speed is reached, before finally spooling up to the commanded thrust.

Good info, thanks!

The A330 Trents hav e the same feature, known in that case as MEASTO, Modified Engine Acceleration Schedule for TakeOff.

Imagine having to do all of this back in the steam gauge days. No wonder they needed a FE.

Wasn’t that difficult, the pilots moved the throttles up to stabilize at 1.4 EPR on the JT8D, when stable, set takeoff thrust. It wasn’t as accurate or precise, but it worked on millions of takeoffs. As a B727 “wrench”, I just watched.

Starlionblue wrote:

I'll add that with a tailwind or crossind above 20 knots, the A350 thrust setting procedure is bit more involved.

- Initially move the thrust levers from idle to the position that gives 25% thrust*.
- Once thrust is stabilised, progressively move the thrust levers to reach the following:
--- At 20 knots ground speed, thrust levers at CL (Climb detent).
--- At 40 knots ground speed, thrust levers at FLX or TOGA (Flex or TOGA detents).

Thrust is set in "steps" to mitigate flow disturbances in case of tailwind. It seems plausible that the A380 procedure is similar. Was there a tailwind or significant crosswind on the day of the video?

* The A350 has a synthetic linear thrust indication (as well as N1).

May I ask, what exactly is a synthetic linear thrust indication system?

SaieshPai wrote:

Starlionblue wrote:

I'll add that with a tailwind or crossind above 20 knots, the A350 thrust setting procedure is bit more involved.

- Initially move the thrust levers from idle to the position that gives 25% thrust*.
- Once thrust is stabilised, progressively move the thrust levers to reach the following:
--- At 20 knots ground speed, thrust levers at CL (Climb detent).
--- At 40 knots ground speed, thrust levers at FLX or TOGA (Flex or TOGA detents).

Thrust is set in "steps" to mitigate flow disturbances in case of tailwind. It seems plausible that the A380 procedure is similar. Was there a tailwind or significant crosswind on the day of the video?

* The A350 has a synthetic linear thrust indication (as well as N1).

May I ask, what exactly is a synthetic linear thrust indication system?

Traditionally, the engine command instrument would be N1 (fan rotation speed), or in some cases EPR (Engine Pressure Ratio). However, these are non-linear in relation to thrust. For example with N1, 15-25% gives pretty much nothing. 25-40% gives a little bit of oomph but is barely above idle. All of a sudden above 40% things start happening and every % makes a big difference.

On the A350, there is a linear thrust indication which is not directly related to any rotation speed or pressure. It simply tells you how many % of max thrust you are getting. Synthetic because it is calculated, not derived from an indication.

Starlionblue wrote:

SaieshPai wrote:

Starlionblue wrote:

I'll add that with a tailwind or crossind above 20 knots, the A350 thrust setting procedure is bit more involved.

- Initially move the thrust levers from idle to the position that gives 25% thrust*.
- Once thrust is stabilised, progressively move the thrust levers to reach the following:
--- At 20 knots ground speed, thrust levers at CL (Climb detent).
--- At 40 knots ground speed, thrust levers at FLX or TOGA (Flex or TOGA detents).

Thrust is set in "steps" to mitigate flow disturbances in case of tailwind. It seems plausible that the A380 procedure is similar. Was there a tailwind or significant crosswind on the day of the video?

* The A350 has a synthetic linear thrust indication (as well as N1).

May I ask, what exactly is a synthetic linear thrust indication system?

Traditionally, the engine command instrument would be N1 (fan rotation speed), or in some cases EPR (Engine Pressure Ratio). However, these are non-linear in relation to thrust. For example with N1, 15-25% gives pretty much nothing. 25-40% gives a little bit of oomph but is barely above idle. All of a sudden above 40% things start happening and every % makes a big difference.

On the A350, there is a linear thrust indication which is not directly related to any rotation speed or pressure. It simply tells you how many % of max thrust you are getting. Synthetic because it is calculated, not derived from an indication.

As a first-order approximation, thrust scales as the square of N1. If you spin a fan blade at twice the speed, it'll travel through twice the molecules (2m) and accelerate them to twice the speed (2a), so you end up with 4F=2m*2a. This obviously ignores the core flow, blade flex, thrust lapse, etc. When you're at high N1, you're all the way up the right side of the parabola.

LH707330 wrote:

Starlionblue wrote:

SaieshPai wrote:

May I ask, what exactly is a synthetic linear thrust indication system?

Traditionally, the engine command instrument would be N1 (fan rotation speed), or in some cases EPR (Engine Pressure Ratio). However, these are non-linear in relation to thrust. For example with N1, 15-25% gives pretty much nothing. 25-40% gives a little bit of oomph but is barely above idle. All of a sudden above 40% things start happening and every % makes a big difference.

On the A350, there is a linear thrust indication which is not directly related to any rotation speed or pressure. It simply tells you how many % of max thrust you are getting. Synthetic because it is calculated, not derived from an indication.

As a first-order approximation, thrust scales as the square of N1. If you spin a fan blade at twice the speed, it'll travel through twice the molecules (2m) and accelerate them to twice the speed (2a), so you end up with 4F=2m*2a. This obviously ignores the core flow, blade flex, thrust lapse, etc. When you're at high N1, you're all the way up the right side of the parabola.

I guess this also explains some airplanes spooling the engines up to "flight idle" when flaps/gear etc are past a certain point, so in the event of a go-around you are already a bit up the power curve.

77west wrote:

LH707330 wrote:

Starlionblue wrote:

Traditionally, the engine command instrument would be N1 (fan rotation speed), or in some cases EPR (Engine Pressure Ratio). However, these are non-linear in relation to thrust. For example with N1, 15-25% gives pretty much nothing. 25-40% gives a little bit of oomph but is barely above idle. All of a sudden above 40% things start happening and every % makes a big difference.

On the A350, there is a linear thrust indication which is not directly related to any rotation speed or pressure. It simply tells you how many % of max thrust you are getting. Synthetic because it is calculated, not derived from an indication.

As a first-order approximation, thrust scales as the square of N1. If you spin a fan blade at twice the speed, it'll travel through twice the molecules (2m) and accelerate them to twice the speed (2a), so you end up with 4F=2m*2a. This obviously ignores the core flow, blade flex, thrust lapse, etc. When you're at high N1, you're all the way up the right side of the parabola.

I guess this also explains some airplanes spooling the engines up to "flight idle" when flaps/gear etc are past a certain point, so in the event of a go-around you are already a bit up the power curve.

Yes definitely. If nothing else, there are minimum spool-up time requirements that need to be met (max 6 seconds to TOGA thrust on a go-around if memory serves), and the engines might have to be at a higher idle to satisfy them.

Starlionblue wrote:

77west wrote:

LH707330 wrote:

As a first-order approximation, thrust scales as the square of N1. If you spin a fan blade at twice the speed, it'll travel through twice the molecules (2m) and accelerate them to twice the speed (2a), so you end up with 4F=2m*2a. This obviously ignores the core flow, blade flex, thrust lapse, etc. When you're at high N1, you're all the way up the right side of the parabola.

I guess this also explains some airplanes spooling the engines up to "flight idle" when flaps/gear etc are past a certain point, so in the event of a go-around you are already a bit up the power curve.

Yes definitely. If nothing else, there are minimum spool-up time requirements that need to be met (max 6 seconds to TOGA thrust on a go-around if memory serves), and the engines might have to be at a higher idle to satisfy them.

This is why many jets are forced to use flaps on approach, because the engines need to be spooled up enough to meet the requirement, and that thrust setting would preclude a stable approach without the added drag.

I just went down the rabbit hole on the cert standards. In the US, 25.119 says it needs to be 8 seconds in a go-around:
https://www.ecfr.gov/current/title-14/c ... ion-25.119

33.73(b) on engines says this:
"From the fixed minimum flight idle power lever position when provided, or if not provided, from not more than 15 percent of the rated takeoff power or thrust available to 95 percent rated takeoff power or thrust in not over 5 seconds. The 5-second power or thrust response must occur from a stabilized static condition using only the bleed air and accessories loads necessary to run the engine. This takeoff rating is specified by the applicant and need not include thrust augmentation. "

https://www.ecfr.gov/current/title-14/c ... tion-33.73

Edit to add: looks like we had this topic way back when: viewtopic.php?t=741469

Wow! That old thread already had a contribution from Starlionblue! We have a veteran on the page!

Edit: probably one of his first posts!

Aircellist wrote:

Wow! That old thread already had a contribution from Starlionblue! We have a veteran on the page!

Edit: probably one of his first posts!

Ha yes. I saw that. Long I even had a PPL.

GalaxyFlyer wrote:

77west wrote:

Starlionblue wrote:

Good info, thanks!

The A330 Trents hav e the same feature, known in that case as MEASTO, Modified Engine Acceleration Schedule for TakeOff.

Imagine having to do all of this back in the steam gauge days. No wonder they needed a FE.

Wasn’t that difficult, the pilots moved the throttles up to stabilize at 1.4 EPR on the JT8D, when stable, set takeoff thrust. It wasn’t as accurate or precise, but it worked on millions of takeoffs. As a B727 “wrench”, I just watched.

Yep, move the thrust levers to roughly straight up, listen for "1.4 Checks!" push them up close to the takeoff setting bugs while peeking back and forth between the centerline and EPR needle movement, use the wonderful 727 feature of voice command and call "Set reduced/max thrust" and a hand would come up from the back and do all the fine adjustment work for you.

So boring now on the A320 series.