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757 Wheel Coast  
User currently offlineOkforalll From , joined Dec 1969, posts, RR:
Posted (13 years 11 months 5 days 20 hours ago) and read 873 times:

While on a flight last week on a DL 757-200, the 2nd officer came on the intercom shortly after takeoff and announced that it would be necessary to allow the wheels to come to a stop without the use of wheel brakes before they could be stowed. He made us aware of this since the time the geer was retracted was unusually long. Anyone know why they chose to do this?

6 replies: All unread, jump to last
 
User currently offlineHeavyJet From , joined Dec 1969, posts, RR:
Reply 1, posted (13 years 11 months 5 days 18 hours ago) and read 835 times:

Sounds like they had a brake deactivated.

Normally the main gear wheels are braked automatically when the landing gear handle is raised. If they weren't, gyroscopic principle (like holding a spinning bicycle tire in your hand and moving it around) would cause undo stress on the gear as it's retracted.

If a brake had been deactivated the crew would have to leave the gear down for a couple of minutes after T/O to allow the wheel to spin down on it's own.


User currently offlineSk902hvy From United States of America, joined Jan 2000, 64 posts, RR: 0
Reply 2, posted (13 years 11 months 5 days 18 hours ago) and read 825 times:

How much drag would the lowered gear create and would there be a speed restriction on climb out?

Thanks,
sk902hvy


User currently offlineAAR90 From United States of America, joined Jan 2000, 3474 posts, RR: 46
Reply 3, posted (13 years 11 months 5 days 18 hours ago) and read 830 times:

Probably just hot brakes. Many new 757 captains have a tendency to "ride the brakes" to keep taxi speeds lower on lightly loaded aircraft. Probably noticed the brake temp as they reached for the gear handle which is probably why the PA was done after takeoff instead of before takeoff.

Just a guess though. It could also have been some missing rub strips in the wheel well(s). Rub strips rub against the tires to stop their rotation after gear is up and in the wells. Not that uncommon, but every time I've experienced this the captain made a PA prior to takeoff.



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlineOkforalll From , joined Dec 1969, posts, RR:
Reply 4, posted (13 years 11 months 5 days 18 hours ago) and read 818 times:

Thanks it all now makes sense. As to the climb rate etc with the geer down, as overpowered as the '57 is I didn't notice anything unusual. Just a bit more engine noise than normal with the wheels down.

User currently offlineAAR90 From United States of America, joined Jan 2000, 3474 posts, RR: 46
Reply 5, posted (13 years 11 months 5 days 17 hours ago) and read 814 times:

>How much drag would the lowered gear create and would there be a speed restriction on climb out?

Lots and lots of drag.

270 knots indicated speed limit for gear in transit.



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlineDC-9CAPT From , joined Dec 1969, posts, RR:
Reply 6, posted (13 years 11 months 5 days 6 hours ago) and read 787 times:

What happened is not all that uncommon. I would suspect that the most likely cause was hot brakes, as AAR-90 pointed out. Also, depending on the aircraft's ground turn time and SLC air temps, the brakes may have been hot already and didn't get sufficient time to cool.

Just to give an idea of the speed restrictions regarding the landing gear for an aircraft Other than the 757:
The max speed on the DC-9 to extend the gear is 300kts
The retract speed is 250kts in our manual.
The max tire speed is 195 kts.

On airlines that operate jets on multiple hops to short fields, they often extend the gear for an extended period of time to cool the brakes. An example is Air Mike's 727s--lots of short hops to small island airstrips where this happens a lot.


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