goinv
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When To Deploy Landing Gear?

Sat Jul 09, 2005 3:35 am

When do airliners put their landing gear down?

Is is below a certain altitude? Or a certain distance from the runway?

The reason for my question is this...in these cost conscious times (when extended landing gear obviously causes drag and hence higher fuel consumption) I see aircraft with their gear down whilst still some distance from the airport. If the rule is "gear down when below xxx altitude" what do the airlines hope to achieve by this from a safety point of view? Having gear down is hardly going to help if an emergency exists over a city on the approach to an airport!

You views/comments would be appreciated
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highflyer9790
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RE: When To Deploy Landing Gear?

Sat Jul 09, 2005 3:50 am

Usually its when the approach has been established and the aircraft is at or around 1500AGL. it is also part of the landing checklist which is done before finals.
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DColeMAN
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RE: When To Deploy Landing Gear?

Sat Jul 09, 2005 3:53 am

They usually extend the landing gear depending on how many miles they are from the airport or how fast/slow their airspeed is. The average distance to drop the gear is around 6-10 miles from the threshold of the runway (obviously again this depends on airspeed, altitude, size of the aircraft etc etc).

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Starlionblue
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RE: When To Deploy Landing Gear?

Sat Jul 09, 2005 5:52 am

Before you hit the ground? Big grin
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buckfifty
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RE: When To Deploy Landing Gear?

Sat Jul 09, 2005 6:21 am

I suppose it depends on the SOP's that the airline employs, but 1500 AGL is definitely too low for gear deployment in most circumstances. By 1500 AGL, the aircraft should be fully configured for landing already. Putting out gear at such a low level is risky, as the aircraft may become unstable due to the extra drag created, and thus lose the g/s if one isn't careful. By 1000 AGL, if you're still struggling with the ILS, might as well go around.

We tend to put our gear down when we're established on the glideslope (or in case of a VOR or NDB, the start of the final descent), but that can change depending on the glideslope interception height. If that's the case, between 2500-3000 ft on finals is a good guideline, with consideration of the flap deployment regimen.
 
AJ
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RE: When To Deploy Landing Gear?

Sat Jul 09, 2005 10:15 am

On a standard delayed drag approach we normally extend the gear at about 2,000'. Flying a non precision approach we must fully configure before the final descent point.

The exception is Runway 34L and 34R in Narita where the undercarriage must be lowered before crossing the coast, about 15nm from memory!
 
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VirginFlyer
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RE: When To Deploy Landing Gear?

Sat Jul 09, 2005 10:57 am

The old story we get told every other week (not certain how much truth there is in it):

Aircraft passes through 200 feet, gear still up
FO: "Captain, are you happy with the position of the landing gear?"
Captain: "Gear down, please!"

V/F
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PhilSquares
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RE: When To Deploy Landing Gear?

Sat Jul 09, 2005 11:24 am

At most of the airlines I have worked for, on an instrument approach you have to be stable at no lower than 1000' AGL, 500' for a visual. So, with that said, most SOPs have a policy of gear extension. At my airline, on an ILS it's at one dot prior to G/S interception. and just prior to G/S interception, landing flaps. For a non-precision, it's prior to the FAF and landing flaps at the FAF.
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CX Flyboy
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RE: When To Deploy Landing Gear?

Sat Jul 09, 2005 12:27 pm

For us, it used to be landing configuration and stable at 1000ft AGL, but now it is 1500ft. On the 777, it takes about 300-350ft to put the gear down, so at about 1900ft, down it goes.
 
SlamClick
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RE: When To Deploy Landing Gear?

Sat Jul 09, 2005 10:55 pm

Quoting PhilSquares (Reply 7):
At most of the airlines I have worked for, on an instrument approach you have to be stable at no lower than 1000' AGL, 500' for a visual. So, with that said, most SOPs have a policy of gear extension. At my airline, on an ILS it's at one dot prior to G/S interception. and just prior to G/S interception, landing flaps.

I think this is a pretty common standard. It should be mentioned that the gear must be down before flaps can be extended beyond the takeoff setting or a horn (which cannot be silenced) will sound. So it is maneuver flaps, then gear, then landing flaps. The plane is not "stabilized" until landing flaps are set, you are on approach speed and established, descending on the glide slope.

One dot does seem to work pretty well with most jetliners.

As has been said in other threads, the landing gear is a pretty good speedbrake on most types. If ATC has held us high or fast, in close we may use it early to get slowed. Typically the flap speeds are more restrictive than the gear extension speed limits and it is, on average, harder on the airframe to extend flaps at the top end of their speed envelope than the gear.

At busy airports, the realities of traffic load often force controllers to give clearances like "maintain 180 to the marker, cleared the ILS two-seven right approach." In a case like this we might put it down a bit late and then have to be rather agressive with getting the rest of the flaps down so we can be slowed to our approach speed by 1000 AGL.
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jeffry747
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RE: When To Deploy Landing Gear?

Sun Jul 10, 2005 5:10 am

I would like to add a question to the original post: For each model of airliner, what is the max gear down speed?
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learpilot
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RE: When To Deploy Landing Gear?

Sun Jul 10, 2005 5:53 am

When do airliners put their landing gear down?

Hopefully sooner than Air India.

http://www.natca.org/mediacenter/ALEastern1.msp

Here's the audio from the tower. Click on "Eastern Region".

http://www.natca.org/mediacenter/ALTapes.msp
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AJ
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RE: When To Deploy Landing Gear?

Sun Jul 10, 2005 9:02 am

Quoting Jeffry747 (Reply 10):
I would like to add a question to the original post: For each model of airliner, what is the max gear down speed?

For the Boeing 767 it's 270kias/M0.82;
for the Boeing 747-400 it's the same, or 320kias/M0.82 with the gear already extended.
 
HaveBlue
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RE: When To Deploy Landing Gear?

Mon Jul 11, 2005 2:27 am

Learpilot that story was amazing, as was the audio from the tower. Phew that was close.
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Starlionblue
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RE: When To Deploy Landing Gear?

Mon Jul 11, 2005 3:10 am

Quoting AJ (Reply 12):
Quoting Jeffry747 (Reply 10):
I would like to add a question to the original post: For each model of airliner, what is the max gear down speed?

For the Boeing 767 it's 270kias/M0.82;
for the Boeing 747-400 it's the same, or 320kias/M0.82 with the gear already extended.

So as I understand it. the max gear down speed is higher than the gear extension speed on many airliners. You can in other words put the gear down at max gear extension speed then accelerate.

Or did I get that wrong?
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SlamClick
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RE: When To Deploy Landing Gear?

Mon Jul 11, 2005 3:43 am

Quoting Starlionblue (Reply 14):
So as I understand it. the max gear down speed is higher than the gear extension speed on many airliners.

Absolutely correct.

The gear DOWN and locked or UP and locked is usually stronger than the gear in-transit.

A couple of things at work here. One is that when locked down, the mechanical linkage is over-center and latched. Another is that while in-transit, there are normally other doors open which do not have the strength of the gear itself. Various doors may open, then close during extension and retraction.

It is not uncommon for the gear retraction speed to be the most limiting, especially on planes with a nosegear that retracts forward.

Quoting Starlionblue (Reply 14):
You can in other words put the gear down at max gear extension speed then accelerate.

Possibly, but that acceleration is going to cost you quite a lot of energy, fuel or altitude!  Smile
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N766UA
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RE: When To Deploy Landing Gear?

Tue Jul 12, 2005 3:52 am

Quoting Starlionblue (Reply 14):
So as I understand it. the max gear down speed is higher than the gear extension speed on many airliners.

UPS once diverted a 742 to CLE because the gear would not retract. He flew all the way from Louisville with it down and, though I don't remember the exact speed, I know he cruised somewhere in the 300kt range the whole way.
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loggat
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RE: When To Deploy Landing Gear?

Wed Jul 13, 2005 3:14 am

On the ERJ-145, the gear must be down and locked prior to 1200' AGL otherwise an unsilenceable horn goes off with a master warning. The max speed for extension/extended gear operation is 250 kts. The maximum speed for retraction is 200 kts.
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AJ
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RE: When To Deploy Landing Gear?

Sat Jul 16, 2005 6:06 pm

Another reason for a higher Vle than Vlo is the independent gear doors. On the 747 the gear doors are complex and multi hinged and can be damaged in too high an airflow. The body gear well doors are the most venerable.
 
A3204eva
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RE: When To Deploy Landing Gear?

Sun Jul 17, 2005 8:48 pm

Usually when passing around 2000ft or when they begin to intercept the glideslope
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flykal
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RE: When To Deploy Landing Gear?

Sun Jul 17, 2005 10:29 pm

During unsuccessful union negotiations, dropping the gear down 20nm out and being in full landing configuration can work wonders. You see, management don't usually listen to pilot union requests, but they do listen when the dollars start doing the talking. The earlier you drop the gear/flaps, the higher the fuel burn.

If all 400 + movements / day are following these guidelines, then you can imagine it burns through quite a bit of extra gas.

Let the $$$'s do the talking!
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skibum9
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RE: When To Deploy Landing Gear?

Fri Jul 22, 2005 11:30 am

I drop my gear just prior to intercepting the glideslope on an ILS, usually about half a dot. On a non-precision approach, I must be fully configured prior to final descent.
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