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Paul12

B-737 Landing Gear Question

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How does one know when to lower the landing gear ? I noticed that whenever I go to flaps 15 there is a sound like a buzzer and when

I lower the gear this sound stops.

Is that indeed a sign for landing gear down ? Are there any other indications ?

 

Hubert Werni


Herbert Werni

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For ILS approaches, the B737 FCOM recommends lowering the gear when the glide slope becomes alive (after the localizer has been captured). For one major virtual airline, the gear is lowered at either 9 NM from the destination airport or when the glide slope becomes alive, whichever occurs later in the approach. If necessary, the gear can be lowered earlier for additional drag.

 

On the B747, the master warning sounds if the gear has not been lowered by flaps 25. A similar safety feature probably exists on the B737.


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Owen
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In the last few years, many airlines have begun lowering the gear as late as possible given no safety issues primarily to save fuel. This fuel saving also extends to not using engine reversers unless absolutely necessary. On many flights Ive taken in the past couple years this has been very obvious, especially heavy braking with no reverse thrust.


Ron W

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In the last few years, many airlines have begun lowering the gear as late as possible given no safety issues primarily to save fuel.

On a

, the gear was lowered before any trailing edge flaps were extended. I had a clear view of the PAPI before the abrupt and wobbly localizer intercept bank (which must have neared or exceeded 30 degrees) aligned us with the runway.

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Owen
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On the B747, the master warning sounds if the gear has not been lowered by flaps 25. A similar safety feature probably exists on the B737.

 

That's the horn that Hubert talks about.

 

This fuel saving also extends to not using engine reversers unless absolutely necessary.

 

The use of the reversers is not tied to saving fuel. Engine repairs/changes due to wear and tear cost a whole lot more than a few gallons (maybe less?) of fuel.

 

Is that indeed a sign for landing gear down ?

 

No. It's the airplane telling you forgot to lower the gear.


Kenny Lee
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In the last few years, many airlines have begun lowering the gear as late as possible given no safety issues primarily to save fuel.

 

In Ryanair gear and flaps 15 extension is delayed till 4 or 5nm to runway.

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Similarly on this side of the Atlantic. Also, agree on the wear and tear re reversers, however, I was told

by a Capt that it was also a fuel issue. Additionally, they often taxi with as few engines as necessary.


Ron W

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Gear must be lowered before you extend flaps past 10 degrees. If you select flap 15 (or 25/30/40) then you get the configuration warning horn. Lowering the landing gear will cancel the horn. (So will reducing flap back to 10, but that's not useful when on approach and not initiating a go around.)

 

Gear extention creates drag. Gear has some extension limits, however if you are already at flap 5, you are well below these limits anyway (otherwise you are exceeding flap 5 limits and the flaps are now damaged).

 

Most real world airlines have a requirement to be stabilized and configured for landing before a certain point on the approach. If you have gear/flaps not configured for landing, Landing checklists not done, not established on the final approach profile (too high/low/fast) by a specific height or distance from the runway, you should go around. The airline I simulate most often has a 1000ft "stable" altitude.

 

This means you can only continue the approach if Gear has already been selected down and is showing 3 greens (and landing checklist has been completed) before you hit 1000ft above the runway altitude. Flaps can be "holding" for final extension a little longer.


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How does one know when to lower the landing gear ? I noticed that whenever I go to flaps 15 there is a sound like a buzzer and when

I lower the gear this sound stops.

Is that indeed a sign for landing gear down ? Are there any other indications ?

 

Hubert Werni

 

Long time ago I red a tutorial where it says the the best point to lower the gear is when on ILS (LOC already captured) and the GS is one point higher before capture.

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I usually lower the gear about 10-15nm from the airport. At this point I am usually at flaps 5 at least and at my final altitude before finals.

 

 

Remy Mermelstein

Remymerm@aol.com

777-300 FS Pilot


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A lot depends on the type as well. A320's and B737's not usually before 8 miles out. A retired Lufthansa Capt told me that in a 747, the landing gear came out one indicator prior to glideslope capture. Mostly because that's a plane that you need to be well ahead of the curve in terms of control and handling due to size and weight. Probably typical for any of the "heavies".


Ron W

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The use of the reversers is not tied to saving fuel. Engine repairs/changes due to wear and tear cost a whole lot more than a few gallons (maybe less?) of fuel.

 

Actually, it has everything to do with saving fuel. Changing brakes is a lot cheaper than the cost of fuel....and even though it's "a few gallons" of fuel, multiply that few gallons times several legs a day times a few thousand aircraft, and it's a little more than a few gallons. It's also the same reason why airlines will use the maximum derate when taking off,

 

Lowering the gear is done when you need it to be done. If your high and fast, drop the gear. It is recommended to have it out at g/s capture, but as long as you get into landing configuration, by 1000ft, you're good to go. The landing gear warning buzzer will sound at flaps 15 if the gear is not out. I always drop it at flaps 15 anyways.


Matt L.

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You can silence the horn with a button on the rear of the throttles until you gpws starts to make the same alert. And that is how it is done in rw.

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In my real world flying we do this. ILS-Gear down at GS movement and flaps landing a dot above. Non-precision-Gear down at the FAF unless circling. VFR pattern-Gear down abeam the threshold on downwind. In every aircraft I've flown, we used the thrust reversers. Saved us on brakes, man hours and down time for brake changes. In our ops, we changed brakes at 50% life just incase an aircraft was stuck out for extended periods. In the DC10, we would only use 1 and 3 when at airports with minimal support. The number 2 was difficult due to it's height above the ground. It required stands and equipment to reach it. In all my years of flying, i've only had 1 thrust reverser issue and it was the all ways neglected number 2 on the DC10. In the G5/550, we use reversers to control speed during taxi. 2 to slow down and 1 to maintain speed. At std day at max landing weight, I can stop a 550 in 6,280ft with both reversers and no braking.

 

That horn is telling you that you have flaps extended to approach with the throttles at idle. The aircraft's way of reminding you that your gear is retracted. The G3 was annoying with that horn. It would sound anytime you put the throttles below 70 degrees with the gear retracted. It was loud and blared through the crew interphone system. You had to hit the silence button on the throttle anytime you reduced power. For each time you allow the horn to sound, you owe a beer.

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Later deployment of gear and flaps on finals is partly for noise abatement reasons. Have a read of this NASA research:

 

http://ntrs.nasa.gov..._2010025667.pdf

 

Iain Smith

 

Edit - Well the pdf document opened once for me but now it won't open at all and this link is useless! Sorry!

 

Edit no. 2 - Try this link to a different NASA document:

 

http://www.aeronautics.nasa.gov/pdf/asm_presentations_airframe_noise_reduction.pdf

 

Iain Smith

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