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Delayed Undercarriage Retraction  
User currently offlineSapphireLHR From United Kingdom, joined Mar 2006, 103 posts, RR: 0
Posted (8 years 1 month 3 days 11 hours ago) and read 2889 times:

Working at LHR I have often noticed that many A319, A320 airbuses tend to delay the retraction of the undercarriage on takeoff. It is not a specific airline thing or on particularly hot / cold days. Why do they do it ? Surely it would cause a massive drag at a time that it would be a disadvantage to enable an efficient climb. Ive asked several people and no one has a specific answer.

Thanks, take care and have a good day.

19 replies: All unread, jump to last
 
User currently offlineCVG2LGA From United States of America, joined Feb 2005, 630 posts, RR: 1
Reply 1, posted (8 years 1 month 3 days 7 hours ago) and read 2799 times:

I know from reading on here that delayed retraction is sometimes done to remove brake dust. I'll never be able to find the picture but I saw it in a post awhile back on here.
Tchau
DA-



They don't call em' emergencies anymore. They call em' Patronies.
User currently offlineHorus From Egypt, joined Feb 2004, 5230 posts, RR: 59
Reply 2, posted (8 years 1 month 3 days 7 hours ago) and read 2783 times:

Quoting CVG2LGA (Reply 1):
I'll never be able to find the picture but I saw it in a post awhile back on here.

There are quite a few in the DB


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Horus



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User currently offlineFilejw From United States of America, joined Sep 2000, 359 posts, RR: 1
Reply 3, posted (8 years 1 month 3 days 6 hours ago) and read 2745 times:

Brake cooling....................

User currently offlineLapper From United Kingdom, joined Mar 2002, 1564 posts, RR: 7
Reply 4, posted (8 years 1 month 3 days 6 hours ago) and read 2667 times:

What a fantastically detailed explaination from Filejw there...

There was a thread on this some time ago, one of those things that crops up now and again. It is as Filejw states, to do with brake cooling. There is a great reply in this thread http://www.airliners.net/discussions...ion/read.main/2690168/6/#ID2690168 from Goldenshield:
"The MEL (A deferred maintainance item per the Minimum Equipment List) in question requires that the landing gear be left in the down position for 10 minutes after departure—regardless of time on the ground— and the aircraft must be able to fly in clear air (no visible moisture, to prevent ice build up) in order to facilitate the proper cooling of the braking elements on the wheels prior to being retracted into the wheel well. This is done due to the possibility of the wheels catching fire due to overheating. If the BTMS is inoperative, then the crew would have no way of knowing that the wheels are indeed too hot to retract into the wheel well, and this alternate procedure is applied to meet the requirements of that MEL."


User currently offlineCoyoteguy From Mexico, joined Oct 2001, 442 posts, RR: 0
Reply 5, posted (8 years 1 month 3 days 6 hours ago) and read 2652 times:

Interesting! I once saw an Avianca 757 leave Miami, and keep its undercarriage down until it was out of sight. I never got around to investigating the reason, but I always wondered.

User currently offlineSkidMarque From United Kingdom, joined Jun 2006, 87 posts, RR: 0
Reply 6, posted (8 years 1 month 3 days 5 hours ago) and read 2633 times:

Please excuse the ignorance but why do the brakes need cooling after a departure, surely they haven't taken that much of a hammering during taxi etc, have they ?

I regulalry see arriving aircraft at LHR that peform a missed approach, or go-around. They often leave the gear down much longer than normal during the climb out. Presumbaly the crew have too much on their plate at the time, gear retraction must be way down the list.



DUCK !
User currently offlineFilejw From United States of America, joined Sep 2000, 359 posts, RR: 1
Reply 7, posted (8 years 1 month 3 days ago) and read 2507 times:

Seeing LHR's question is about A320/319. Those A/C brakes are fairly sensitive and tend to heat up easily. Most of these operators most likely are short haul with short turn times so the brakes may not be cool as one might like. The A/C have a brake temp T/O limit of 300 and if you are close to the temp limit and leave the gear down for just a bit the brakes will cool pretty quickly.

User currently onlineMir From United States of America, joined Jan 2004, 21554 posts, RR: 55
Reply 8, posted (8 years 1 month 2 days 22 hours ago) and read 2431 times:

Quoting GBOAG (Reply 6):
surely they haven't taken that much of a hammering during taxi etc, have they

They can, particularly if the plane is heavy or if the day is hot (or both). Some planes have brake fans to deal with that, others do not.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 9, posted (8 years 1 month 2 days 15 hours ago) and read 2296 times:

Brake Cooling,by Extending the Gear for longer time than needed.
Works well.
regds
MEL



Think of the brighter side!
User currently offlineAccess-Air From United States of America, joined Sep 2000, 1939 posts, RR: 13
Reply 10, posted (8 years 1 month 2 days 3 hours ago) and read 2185 times:

Well I would like to say that I have noticed that Airbus planes versus Boeing or McDouglas planes seem to leave their wheels out in the rain and retract very slowly....
I thought the object of the game on take off was to clean up your aircraft aerodynamically as quckly as you can?? Does this not apply to Airbuses? Its just something I noticed and its not just sometimes its ALL the time...
I have seen the break dust as was illustrated in an earlier thread above, but Boeing planes retract their gear in short order or their gear is half way up and tucked away before you see that "dust".
Just an observation I have made....Have any of you noticed this??

Access-Air



Remember, Wherever you go, there you are!!!!
User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 11, posted (8 years 1 month 2 days 3 hours ago) and read 2181 times:

Quoting GBOAG (Reply 6):
Please excuse the ignorance but why do the brakes need cooling after a departure, surely they haven't taken that much of a hammering during taxi etc, have they ?

No but theyve just had to stop the wheels after theyve been accelerated up to high speed during the takeoff roll - cant retract spinning wheels, the centripetal forces have an effect!


User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 12, posted (8 years 1 month 2 days 1 hour ago) and read 2138 times:

Quoting RichardPrice (Reply 11):
No but theyve just had to stop the wheels after theyve been accelerated up to high speed during the takeoff roll - cant retract spinning wheels, the centripetal forces have an effect!

The Auto Retract Actuator stops the MWs on retraction,Snubber pads for the NLG Wheels.
regds
MEL



Think of the brighter side!
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 13, posted (8 years 1 month 1 day 16 hours ago) and read 2030 times:

Quoting RichardPrice (Reply 11):
No but theyve just had to stop the wheels after theyve been accelerated up to high speed during the takeoff roll - cant retract spinning wheels, the centripetal forces have an effect!

Placing the gear handle in the up position applies the brakes and stops the wheels from turning. Leaving the wheels down a even a few seconds longer will allow air between the brake rotors and cool them. The nose wheels are stopped by spin brakes that rub against the wheels once they are up in the wheel well.


User currently offlineUtapao From Thailand, joined Jul 2005, 645 posts, RR: 9
Reply 14, posted (8 years 1 month 1 day 14 hours ago) and read 1986 times:

I've been on many flights with delayed retraction, but the one that sticks in my mind is an AA MD80 DFW-STL in the summer of '87. It was the hottest day of the summer... something like 109 if memory serves... and the pilot actually came on during taxi to advise that due to the heat that day he would be leaving the wheels down longer than normal after takeoff. Been a long time, but seems like he said it was to allow the tires to cool down before reaching altitude, but could have just been his "answer for dummies" response. I just thought it was cool he advised.

I've been on dozens and dozens of flights out of extraordinarily hot places over the years, this was the only time I remember the cockpit advising in advance that he would leave the wheels down longer than normal.



Sawasdee khrab!
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 15, posted (8 years 1 month 1 day 14 hours ago) and read 1982 times:

Quoting Utapao (Reply 14):
I've been on dozens and dozens of flights out of extraordinarily hot places over the years, this was the only time I remember the cockpit advising in advance that he would leave the wheels down longer than normal.

It has very little to do with the air temperature and a lot to do with how heavy the aircraft is, how long it taxis and how much the brakes are used.


User currently offlineJmhluv2fly From United States of America, joined Dec 1999, 559 posts, RR: 0
Reply 16, posted (8 years 1 month 1 day 9 hours ago) and read 1919 times:

One question I would have is why would any gear be left down ten minutes after departure? According to reply number 5: "The MEL (A deferred maintainance item per the Minimum Equipment List) in question requires that the landing gear be left in the down position for 10 minutes after departure—"
I would think that going nearly 200 miles an hour on takeoff
(many airplane tires I have seen have a limit of 200mph) the tires would cool pretty dang on quick, not to mention if you are traveling in the winter the tires and wheel strut assembly are probably getting hit with snow and ice on takeoff anyway, the brake temp wouldnt be an issue unless you had a major breaking somewhere on taxi. Now I have seen breaks to remain pretty hot hours after the airplane (DL MD-88) has been at rest at the gate usually terminating airplane. But when that airplane is zooming throught the air things should cool off pretty quick, thats just my fairly uneducated assesment.
One airplane I have seen to take really long to retract its gear, is the 767 family, particuliarly the 767-200, that thing will be way beyond the end of the runway, probably a good couple thousand feet up before the gear doors fully close after wheel retraction. So I wonder whats going on there?
Simply design? Hot brakes? I notice that in the MD-88/ 717 there is a structure within the gear storeage belly that sticks out and seemingly must have an effect on the tires when they come in contact with this rough structure, perhaps stopping the tire rotation when the gear is retracted into the belly?

JMH-Pensacola, Florida.


User currently offlineVc10 From United Kingdom, joined Nov 2001, 1407 posts, RR: 16
Reply 17, posted (8 years 1 month 1 day 7 hours ago) and read 1866 times:

A lot of the heat in a wheel assembly comes not from the brakes but from the tyre especially when taxing for take off when the aircraft is heavy.
Tyre deformation as the wheel rotates and during turning will heat the tyre considerably, as will the deformation during the take off run.

Some aircraft have brake fans to try and cool the brakes, but these are only really effective when the brakes are released, so during taxing the pilot's use of the brakes can affect the cooling, in that gentle but long applications of the brakes will keep the rotors/stators together for long periods and so inhibit cooling.

littlevc10


User currently offlineChrisMUC From Germany, joined Jul 2006, 66 posts, RR: 0
Reply 18, posted (8 years 1 month 1 day 7 hours ago) and read 1833 times:

Quoting GBOAG (Reply 6):
Please excuse the ignorance but why do the brakes need cooling after a departure, surely they haven't taken that much of a hammering during taxi etc, have they ?

brakes reach their highest temperature 30-60 Min after departure, that's a little surprising but taxing is very stressfull due to the higher gross weight and number of braking actions. Another possibility is to extend the gear earlier, but terrain permitting as in LHR you do it after departure since it's much more effective and you lower the peak temp.


User currently onlineGoldenshield From United States of America, joined Jan 2001, 6003 posts, RR: 14
Reply 19, posted (8 years 1 month 1 day 5 hours ago) and read 1789 times:

Quoting Jmhluv2fly (Reply 16):
I would think that going nearly 200 miles an hour on takeoff
(many airplane tires I have seen have a limit of 200mph) the tires would cool pretty dang on quick, not to mention if you are traveling in the winter the tires and wheel strut assembly are probably getting hit with snow and ice on takeoff anyway, the brake temp wouldnt be an issue unless you had a major breaking somewhere on taxi.

The MEL that I was talking about in the quoted text above is actually the wrong MEL. The BTMS, or Brake Tempurature Monitoring System requires adaquate ground time. The issue in question here is the Gear Bay Overheat Detection System. I was unable to go back and edit the post, and forgot about it. I tend to get the two confused when I'm in a rush, too.  sorry 

Basically, the GBOD is a loop that detects fires in the landing gear, and so the 10 minute thing is there to allow the brakes to cool down enough to prevent any issues. You are correct that any normal takeoff in winter weather will collect snow and ice, but nowhere near the amount it would if left down for 10 minutes. Also, there is possibility of icing on climbout. It my be summer now, but the potential for icing still exists when conditions permit.



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