Just curious: twice recently I’ve seen a BA 787-900 takeoff near my house (6 miles off Rwy 30 at KIAD) - at 2,500-3,000 feet they still have the gear down. No other plane has the gear down this long. In fact, a Lufthansa 747-800 just took off - a bit lower than the BA was - and it was in a clean config.

Just wondering if this is BA SOP or why they keep the gear down so long. Thx!

indcd wrote:

Just curious: twice recently I’ve seen a BA 787-900 takeoff near my house (6 miles off Rwy 30 at KIAD) - at 2,500-3,000 feet they still have the gear down. No other plane has the gear down this long. In fact, a Lufthansa 747-800 just took off - a bit lower than the BA was - and it was in a clean config.

Just wondering if this is BA SOP or why they keep the gear down so long. Thx!

At BA, the flight crew are always served a lovely kidney pie followed by a delightful spotted dick by the flight attendants just as they line up on the runway. So the pilot flying has to finish his meal and order a vodka martini, shaken, not stirred, before he can retract the gear. Other than that, when you see gears down for longer than normal, it's to cool the brakes down after heavy braking on arrival and a relatively short turn-around, so they don't have time to cool off on the ground. Nothing specific to BA, nor to the 787, as far as I know.

And it's Boeing 747-8, not -800

That’s very interesting regarding the short turn times. Anyone have any info on how long breaks typically take to cool down? Let’s say on a 70 degree day?

MalevTU134 wrote:

indcd wrote:

Just curious: twice recently I’ve seen a BA 787-900 takeoff near my house (6 miles off Rwy 30 at KIAD) - at 2,500-3,000 feet they still have the gear down. No other plane has the gear down this long. In fact, a Lufthansa 747-800 just took off - a bit lower than the BA was - and it was in a clean config.

Just wondering if this is BA SOP or why they keep the gear down so long. Thx!

At BA, the flight crew are always served a lovely kidney pie followed by a delightful spotted dick by the flight attendants just as they line up on the runway. So the pilot flying has to finish his meal and order a vodka martini, shaken, not stirred, before he can retract the gear. Other than that, when you see gears down for longer than normal, it's to cool the brakes down after heavy braking on arrival and a relatively short turn-around, so they don't have time to cool off on the ground. Nothing specific to BA, nor to the 787, as far as I know.

And it's Boeing 747-8, not -800

And Boeing 787-9, not -900.

Oh well - so my nomenclature was off - guess I was reverting back to the 737 names. Thanks for the clarity.

SL1200MK2 wrote:

That’s very interesting regarding the short turn times. Anyone have any info on how long breaks typically take to cool down? Let’s say on a 70 degree day?

Today was a 3 1/2 hour turn. That’s seems like a fairly long time. And it’s 55 degrees today.

Only reason I can think of is to cool the brakes. Short turn times coupled with sitting in a long taxi line repeatedly using the brakes. Did it a few times in the E145 but never as long as you’re describing

It’s to cool the brakes. I’ve seen Airbus narrow bodies do it also and they even cooling fans that are used in the ground.

Could also be an inop brake. They leave the gear down until the wheels stop spinning. Normally the brakes are used to stop the wheels before retraction. Avoids stresses on the gear components. Think that experiment you did in school where you hold the spinning bike wheel thing on the spinning chair.

Boof02671 wrote:

It’s to cool the brakes. I’ve seen Airbus narrow bodies do it also and they even cooling fans that are used in the ground.

Brake fans are an option on the A330. I think the same on the A32x.

Starlionblue wrote:

Boof02671 wrote:

It’s to cool the brakes. I’ve seen Airbus narrow bodies do it also and they even cooling fans that are used in the ground.

Brake fans are an option on the A330. I think the same on the A32x.

I can confirm that. My company doesn’t have brake fans on A320/321s but still does short (35-40 minutes) turnarounds even on airports with a very short, 1700m runway, however there are a few things you can do to keep brake temperatures under control. One of them is using flap full and maximum reverse for landing (using full reverse is not a very economic option as it generates additional costs, however it’s preferable over a delay to cool the brakes). If a long taxi after landing is expected single engine taxi also helps to reduce the amount of energy that has to be absorbed by the brakes (not always an option, especially if there is a big upslope on a taxiway somewhere). A proper braking technique also helps - the one recommended by Airbus to let the aircraft accelerate to 30kts and then using brakes to bring is back to 10kts to let it accelerate again works quite well to reduce the number of brake applications and also helps to keep the temperatures down. Once the chocks are confirmed in place after parking, releasing the parking enables faster brake cooling. Therefore brake cooling is usually not a big issue if proper techniques are applied.
Even on aircraft that are equipped with brake fans there can be MEL items that result in longer cooling times (either the fans themselves or the brake temperature indication system).

SL1200MK2 wrote:

That’s very interesting regarding the short turn times. Anyone have any info on how long breaks typically take to cool down? Let’s say on a 70 degree day?

On the A330 I can have the brakes at 400 deg C 40 minutes before push and it will be okay for a 20 minute taxi, they will drop around 5 degC per minute. It is preferable to have the carbon brakes warm rather than cold anyway, they perform better when warm with less wear. Takeoff can be commenced with brakes temperature up to 300 deg C. If you know the brakes are warm from the previous sector and you know you have a short turn around, nothing wrong with putting the gear down early to cool them.

The OAT has little effect on cooling time, airflow over the brakes is what cools them best. Portable brake fans do that exactly.

Normally the reason for leaving the gear down is not brake cooling, it is for brake related MEL procedure, and we wait for whatever time is specified in the MEL for the gear to stop spinning before retracting.

For example on the 787 if any of the following are inoperative the MEL requires the gear to left down
Antiskid control system - leave gear down for 2 minutes after departure
Nose gear spin down brake - leave gear down for 2 minutes after departure
Wheel brake system - leave gear down for 2 minutes after departure

I also recall being on a BA TriStar LHR-JFK and there was an air con problem- the pilot said the gear doors world remain open longer than normal in order to get some cooler air into the cabin. Whether this explanation was true or not I don't know, but it worked- the cabin was unpleasantly warm on departure and after a few minutes airborne the temperature was normal.

zeke wrote:

SL1200MK2 wrote:

That’s very interesting regarding the short turn times. Anyone have any info on how long breaks typically take to cool down? Let’s say on a 70 degree day?

On the A330 I can have the brakes at 400 deg C 40 minutes before push and it will be okay for a 20 minute taxi, they will drop around 5 degC per minute. It is preferable to have the carbon brakes warm rather than cold anyway, they perform better when warm with less wear. Takeoff can be commenced with brakes temperature up to 300 deg C. If you know the brakes are warm from the previous sector and you know you have a short turn around, nothing wrong with putting the gear down early to cool them.

The OAT has little effect on cooling time, airflow over the brakes is what cools them best. Portable brake fans do that exactly.

Normally the reason for leaving the gear down is not brake cooling, it is for brake related MEL procedure, and we wait for whatever time is specified in the MEL for the gear to stop spinning before retracting.

For example on the 787 if any of the following are inoperative the MEL requires the gear to left down
Antiskid control system - leave gear down for 2 minutes after departure
Nose gear spin down brake - leave gear down for 2 minutes after departure
Wheel brake system - leave gear down for 2 minutes after departure

How short would your sector have to be to still have warm brakes on landing?

I once saw the aftermath of a wet and then frozen brake which seized at landing - it obviously had to be rejected.
But granted the brake temp at take-off was under 190°C after a short tax and a couple hours flight and the water wasn't fully gone out of the brake at take-off.

Incidentally it takes months to make a carbon brake.
https://www.meggitt.com/insights/how-do ... on-brakes/

zeke wrote:

Normally the reason for leaving the gear down is not brake cooling, it is for brake related MEL procedure, and we wait for whatever time is specified in the MEL for the gear to stop spinning before retracting.

For example on the 787 if any of the following are inoperative the MEL requires the gear to left down
Antiskid control system - leave gear down for 2 minutes after departure
Nose gear spin down brake - leave gear down for 2 minutes after departure
Wheel brake system - leave gear down for 2 minutes after departure

Super helpful and insightful. Thanks, zeke.

ReverseFlow wrote:

How short would your sector have to be to still have warm brakes on landing?

60-90 min, also depends how heavy you are landing each time

zeke wrote:

ReverseFlow wrote:

How short would your sector have to be to still have warm brakes on landing?

60-90 min, also depends how heavy you are landing each time

Thanks.
Short flight for an A330.
Where's the A330R when you need it

ReverseFlow wrote:

zeke wrote:

ReverseFlow wrote:

How short would your sector have to be to still have warm brakes on landing?

60-90 min, also depends how heavy you are landing each time

Thanks.
Short flight for an A330.
Where's the A330R when you need it

Short compared to the design range, I suppose, but not really a short sector for an A330 in East and Southeast Asia. Widebodies routinely do 1-3 hour flights.

Starlionblue wrote:

ReverseFlow wrote:

zeke wrote:

60-90 min, also depends how heavy you are landing each time

Thanks.
Short flight for an A330.
Where's the A330R when you need it

Short compared to the design range, I suppose, but not really a short sector for an A330 in East and Southeast Asia. Widebodies routinely do 1-3 hour flights.

Same here in NZ/AUS. We have plenty of A330, B777, B787 all on the 2.5-3.5 hour trans Tasman flights. Heck, we used to have EK A380s as well!

Starlionblue wrote:

Boof02671 wrote:

It’s to cool the brakes. I’ve seen Airbus narrow bodies do it also and they even cooling fans that are used in the ground.

Brake fans are an option on the A330. I think the same on the A32x.

That’s interesting. Boeing hasn’t offered brake fans on any model, to my knowledge, for over 20 years. I think they were offered as an option on the 777 pre-2000.

BoeingGuy wrote:

Starlionblue wrote:

Boof02671 wrote:

It’s to cool the brakes. I’ve seen Airbus narrow bodies do it also and they even cooling fans that are used in the ground.

Brake fans are an option on the A330. I think the same on the A32x.

That’s interesting. Boeing hasn’t offered brake fans on any model, to my knowledge, for over 20 years. I think they were offered as an option on the 777 pre-2000.

Anecdotally, it seems to be one of those philosophy differences between Boeing and Airbus. As I understand it, Airbus saves some weight by having less beefy brakes, but this often leads to hotter brakes.

Aircraft design compromise, like many others.

Related question: to what extent does deceleration rate affect brake heating? Doesn't the same amount of energy need to get dissipated either way? The only thing I can think of that would make a big difference is using more TR or spoilers on a longer runway and thus having to do less braking.

LH707330 wrote:

Related question: to what extent does deceleration rate affect brake heating? Doesn't the same amount of energy need to get dissipated either way? The only thing I can think of that would make a big difference is using more TR or spoilers on a longer runway and thus having to do less braking.

Airbus has a brake-to-vacate (BTV) system that allows the pilot to choose a taxiway they want to exit the runway on. This then calculates the deceleration required and applies the brakes accordingly. At the end, the aircraft reaches a certain speed at the taxiway.

Apparently this saves from brake wear. So to answer your question, it's probably better than using max autobrake all the time (and avoids everyone being slammed into their safety belts all the time!).

https://www.flightglobal.com/easa-clear ... 32.article

Max auto brake is a takeoff setting, not used for landing

LH707330 wrote:

Related question: to what extent does deceleration rate affect brake heating? Doesn't the same amount of energy need to get dissipated either way? The only thing I can think of that would make a big difference is using more TR or spoilers on a longer runway and thus having to do less braking.

The deceleration rate does affect the brake heating significantly. The way auto brakes work is that they aim to achieve a constant deceleration rate of the a/c and the energy dissipation is shared between brakes, thrust reverser and aerodynamic drag.

The higher the auto brake setting, the higher share of the total energy is absorbed by the brakes.

On the 787, The lowest auto brake setting results in 50-65% of the energy absorbed by the brakes, as compared to max manual braking.

Thrust reversers also reduce energy absorbed by the brakes and the amount depends on auto brake setting. When the deceleration is high (ie. max auto), the share of energy absorbed by reversers is small.

At low auto brake setting the reversers have time to work and may reduce brake energy by up to ~60%

We can take it even further - it takes approximately 2700-3000m of runway to slow down the airplane to taxi speed with aerodynamic drag and idle reverse thrust only, without touching the brakes*. So on very long runways the brake energy may effectively be zero.

Another issue all together is whether it makes sense to ‘save’ the brakes by keeping them cool. It might have had sense with steel brakes, which are less common these days. OTOH carbon brakes don’t care as much about temperature - in fact, they operate most efficiently when (moderately) hot. Actually, according to some sources, the highest wear occurs during taxi out, when the brakes at cool, rather than on landing…

* disclaimer: I don’t advocate this technique- do whatever your FCOM/FCTM/SOP says.

zeke wrote:

Max auto brake is a takeoff setting, not used for landing

Not to mention, minimum turnaround times are determined by brake energy efficiency on a subsequent rejected takeoff. For instance, if a takeoff and subsequent RTO occurs without sufficient brake cooling from a previous landing, brake efficiency is reduced, increasing the RTO stopping distance.

I'm surprised this hasn't entered into the discussion.

Yikes! wrote:

if a takeoff and subsequent RTO occurs without sufficient brake cooling from a previous landing, brake efficiency is reduced, increasing the RTO stopping distance.

It is my understanding that as long as we honor the "maximum brake temperature limit for takeoff," (300 degrees C A320) the takeoff data--including the stopping distance--will be valid.

We really don't consider turn time as long as we respect the specified max temperature limit before initiating takeoff.

e38

Correct for Airbus

zeke wrote:

Max auto brake is a takeoff setting, not used for landing

Actually Boeing has a Max autobrake setting for landing. The takeoff setting is RTO.

Thanks all, that makes sense.

zeke wrote:

On the A330 I can have the brakes at 400 deg C 40 minutes before push and it will be okay for a 20 minute taxi, they will drop around 5 degC per minute.

400°C?! Jesus christ! When I heard people here talking about hot brakes, I thought it was around 150°C!

400 is not uncommon, 150 on the A330 is very low after landing. It is okay for them to absorb energy.

trent768 wrote:

zeke wrote:

On the A330 I can have the brakes at 400 deg C 40 minutes before push and it will be okay for a 20 minute taxi, they will drop around 5 degC per minute.

400°C?! Jesus christ! When I heard people here talking about hot brakes, I thought it was around 150°C!

You're stopping a 200-tonne aircraft that is doing 140 knots in a few thousand feet. That's a LOT of energy.

Doing the walkaround on a short turn, you can definitely feel the heat coming off the brakes when you check the tyres and brake wear indicators.

trent768 wrote:

zeke wrote:

On the A330 I can have the brakes at 400 deg C 40 minutes before push and it will be okay for a 20 minute taxi, they will drop around 5 degC per minute.

400°C?! Jesus christ! When I heard people here talking about hot brakes, I thought it was around 150°C!

as Zeke mentioned, unlike the brakes on your car (which mostly are iron brake discs) these brakes are carbon-carbon which works better with temperature, and as a reference on the 777 the BTMS (brake temperature monitoring system) the displayable range is from 38°C to 1038°C, with BRAKE TEMP advisory if above 538°C. So 400°C is really just normal operation.

celestar345 wrote:

trent768 wrote:

zeke wrote:

On the A330 I can have the brakes at 400 deg C 40 minutes before push and it will be okay for a 20 minute taxi, they will drop around 5 degC per minute.

400°C?! Jesus christ! When I heard people here talking about hot brakes, I thought it was around 150°C!

as Zeke mentioned, unlike the brakes on your car (which mostly are iron brake discs) these brakes are carbon-carbon which works better with temperature, and as a reference on the 777 the BTMS (brake temperature monitoring system) the displayable range is from 38°C to 1038°C, with BRAKE TEMP advisory if above 538°C. So 400°C is really just normal operation.

I am picking at 1038 °C you have other issues other than just hot brakes!!

77west wrote:

I am picking at 1038 °C you have other issues other than just hot brakes!!

If the pilots decides to ignore all the EICAS messages and get to that point without good reason, then I would say they brought it upon themselves....

Saw a similar thing with this Air India 787 out of Heathrow recently. The gear was still down as it passed 4,000ft.

Often times pilots will advise the tower controller if they need to keep the gear down for an extended period.

zeke wrote:

Max auto brake is a takeoff setting, not used for landing

It is for Boeing. There is a RTO setting for Boeing. I can’t comment on Airbus.

SL1200MK2 wrote:

That’s very interesting regarding the short turn times. Anyone have any info on how long breaks typically take to cool down? Let’s say on a 70 degree day?

I recall Thai Airways operating A300s a very long time ago into CCU (my then home airport). The aircraft used to have a 1:15 ground time. Whenever they braked hard on landing and the landing gear units heated up, a ground a/c unit with vent directed towards them was used to cool them off. Mostly worked and normal gear retraction was achieved. The only crazy guys ive seen (and regularly) were Aeroflot who used to douse the landing gear of their IL86s with buckets of water...

Oh those Russians (with due respects to Boney M).

cheers//Vimanav