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29erUSA187
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Delayed Landing Gear Retraction?

Sat Jun 20, 2015 1:20 am

Hello all,

Earlier today, I was on Mission Bay, near the SAN take off path. As an enthusiast, every time I hear a jet, I look up, but this time, I saw something strange. An AA (LUS) A321 was taking off, at a normal rate of climb, normal speed, everything (at least thats how it looked to me) But the Landing gear were still down, and he was at about 1000-1200 feet up. Normally, the landing gear is retracted right after rotation, before the plane is even visible from Mission Bay.

I have seen this before a few times, but only on Airbii.

What gives?

Thanks for any replies,
29er
 
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Moose135
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RE: Delayed Landing Gear Retraction?

Sat Jun 20, 2015 1:33 am

You'll see that every once in a while. Sometimes, if they have had an excessive taxi route to takeoff, brakes and such may be warm, and they will leave the gear down longer than usual to allow the airflow to help with cooling before retracting it. That would apply to any type, not just Airbus.
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tb727
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RE: Delayed Landing Gear Retraction?

Sat Jun 20, 2015 2:37 am

Yeah, sit at the departure end of 25R in LAS, you'll see a bunch of Airbus doing that for sure. Long taxi, down a slight decline, pretty warm brakes!

That plane probably came into SAN, had a short stay and departed with warm brakes, may not have had brake fans installed, those really help out in avoiding that.
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glen
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RE: Delayed Landing Gear Retraction?

Sat Jun 20, 2015 10:06 am

Another reason for delayed gear retraction can be an inoperative brake.

Under normal conditions all wheels are braked at gear retraction, in order to stop the rotation. Rotating wheels produce strong torque forces onto the landing gear due to gyroscopic precession. In addition a rotating wheel could cause damage in the wheel well.
So if one brake is inoperative, which is usually allowed by MEL, you have to leave the gear down for a specific amount of time, so the rotation of the wheel can stop by itself.
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DocLightning
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RE: Delayed Landing Gear Retraction?

Sat Jun 20, 2015 7:12 pm

Quoting Moose135 (Reply 1):

You'll see that every once in a while. Sometimes, if they have had an excessive taxi route to takeoff, brakes and such may be warm, and they will leave the gear down longer than usual to allow the airflow to help with cooling before retracting it. That would apply to any type, not just Airbus.

So I've always wondered about this: given the fact that on any given takeoff the pilot might have to apply max (or at least hard) braking right before V1, why is it OK to start a takeoff roll with brakes that are already "too warm?"
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rwessel
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RE: Delayed Landing Gear Retraction?

Sat Jun 20, 2015 7:42 pm

Quoting DocLightning (Reply 4):
So I've always wondered about this: given the fact that on any given takeoff the pilot might have to apply max (or at least hard) braking right before V1, why is it OK to start a takeoff roll with brakes that are already "too warm?"

It's not - if the brakes are too hot to handle a stop from V1, you can't take off. It's a different limit that applies to how hot the brakes can be before you stow them in the wheel wells. Remember all that heat has to go someplace - and if the gear is retracted it's going to go into the wheel well, and everything in there. Dangling in the breeze they'll cool off quickly without roasting everything else (and that includes the tires).
 
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longhauler
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RE: Delayed Landing Gear Retraction?

Sat Jun 20, 2015 9:41 pm

Quoting DocLightning (Reply 4):

So I've always wondered about this: given the fact that on any given takeoff the pilot might have to apply max (or at least hard) braking right before V1, why is it OK to start a takeoff roll with brakes that are already "too warm?"

"Too warm" may be a misnomer. A couple things to consider.

First of all, carbon brakes are very very effective when hot, even more effective than when cold. But, they are also very dangerous when they get that hot. Not just bringing them up into the wheel well as mentioned, but also too dangerous to have ground crew anywhere near them. A best care scenario would be the fuse plugs melt causing the tires to deflate, and worse case would be the brakes causing the tires to explode before cooling.

So a reject requiring maximum braking is quite possible and capable, but delicate handling after is certainly required.

Secondly, and more likely ... In an A321, take-off roll can not be initiated with brakes 300C or higher. (or 150C with brake fans, but that's another whole issue!) So, let's say the take-off was started with brakes at 290C. The "Hot Brakes" warning is inhibited from 80kts to liftoff. During the take-off run the brakes exceed 300C but you don't know about it. At liftoff, you get the now uninhibited "hot brake" warning ... what do you do? ... you leave the gear down until temps drop below 300C. That may have been what the OP saw.

The funny thing is that they don't cool down as quickly as one would imagine! I remember years ago taking off from TPA in an A321 and got the hot brake warning at liftoff. We were through 5,000 before the brakes cooled below 300!
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UAL Bagsmasher
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RE: Delayed Landing Gear Retraction?

Sun Jun 21, 2015 2:18 am

On the CRJ-200 I believe the gear is to remain extended for something like 5 min after rotation when the gear bay overheat system loop is on MEL. I'd have to refresh my memory with the MEL book for the BTMS (brake temperature monitoring system) MEL. I thought it had a similar restriction as well.
 
speedbird128
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RE: Delayed Landing Gear Retraction?

Mon Jun 22, 2015 6:28 pm

Out of AUH I once had a B74S with gear extended until passing at least F100 when I lost sight of it... Due to very hot brakes, a ground temp of +49C, and short turnaround.
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Whiteguy
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RE: Delayed Landing Gear Retraction?

Mon Jun 22, 2015 9:44 pm

We don't even have an indication of the brake temp on the B737.....different procedures for different aircraft.
 
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longhauler
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RE: Delayed Landing Gear Retraction?

Tue Jun 23, 2015 3:13 am

Quoting whiteguy (Reply 9):
We don't even have an indication of the brake temp on the B737.....different procedures for different aircraft.

The B737-200s and B737-300s I flew many years ago had "tire screen" and "wheel well fire" warnings. The drill was the same in both cases ... slow down to VLE, drop the gear, accellerate to VMO until the indication extinguishes. Do the newer versions of the B737 not have that? I am guessing without brake temperature indications, this was the next best thing.

As far as I recall, there have been only a few instances of an actual "wheel well fire" where anyone on board survived. (With all the rest where no one survived).

[Edited 2015-06-22 20:17:12]
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Whiteguy
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RE: Delayed Landing Gear Retraction?

Tue Jun 23, 2015 5:29 am

Quoting longhauler (Reply 10):

Quoting whiteguy (Reply 9):
We don't even have an indication of the brake temp on the B737.....different procedures for different aircraft.

The B737-200s and B737-300s I flew many years ago had "tire screen" and "wheel well fire" warnings. The drill was the same in both cases ... slow down to VLE, drop the gear, accellerate to VMO until the indication extinguishes. Do the newer versions of the B737 not have that? I am guessing without brake temperature indications, this was the next best thing.

As far as I recall, there have been only a few instances of an actual "wheel well fire" where anyone on board survived. (With all the rest where no one survived).

[Edited 2015-06-22 20:17:12]

Yeah we have the "wheel well fire" warning but no actual temperature indication. Procedure is the same but even if it goes out land immediately.
 
Fabo
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RE: Delayed Landing Gear Retraction?

Tue Jun 23, 2015 9:08 pm

Wheel well fire is standart on NGs, brake temp an extra option (but available). Wonder how will it be on Max.

IRC there were tables for cooling time of the brakes. Not sure about normal ops, but certainly after RTO you'd take a look.
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HAWK21M
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RE: Delayed Landing Gear Retraction?

Fri Jul 10, 2015 12:55 pm

Most likely a delayed retraction of the gear would be linked to a hot brake after getting Airborne.....The crew will extend the gear for some time to cool the temperature by delaying retraction of the gear.
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gunsontheroof
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RE: Delayed Landing Gear Retraction?

Wed Jul 15, 2015 7:45 pm

I was on a NW A333 departing AMS once years ago and shortly after crossing the Dutch coast, the pilot announced that he was re-extending the gear for a minute because "they weren't cooling down as quickly as we'd like" (or something to that effect). How common is that?
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flylku
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RE: Delayed Landing Gear Retraction?

Wed Jul 15, 2015 10:48 pm

So the little planes I fly have a gear up warning. Do commercial airliners have a gear down warning?

Are the newer carbon brakes better or worse than steel brakes at dissipating heat?
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Starlionblue
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RE: Delayed Landing Gear Retraction?

Wed Jul 15, 2015 11:39 pm

Quoting flylku (Reply 15):
So the little planes I fly have a gear up warning. Do commercial airliners have a gear down warning?

Airliners also have a gear up warning for landing configuration, of course.

I'm not sure if Airbus or Boeing will tell you if you're exceeding Vle with the gear down.

You will get a gear unsafe warning when gear is selected up but remains down. If memory serves, on Airbus the pertinent gear leg indicator will show a red triangle and the lower ECAM screen will show the wheels page with amber for malfunctioning legs and gear doors in the wrong position.
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