Cricri From France, joined Oct 1999, 581 posts, RR: 7 Posted (14 years 1 month 1 week 1 hour ago) and read 1001 times:
A friend of me asked me a question yesterday. It was so simple that I couldn't find the answer AND I HATE IT!
This was his example : during the approach, the pilot lowers the undercarriage with setting the landing gear lever on down position but if for any reason he has to put it on up position before it's complete extension and locking, will the gear begins to go up immediatly or will it first goes down completely and then comes up again?
Help me to find my honour back! Thanks, Cricri.
Ilyushin96M From United States of America, joined Sep 1999, 2609 posts, RR: 13 Reply 1, posted (14 years 1 month 6 days 19 hours ago) and read 938 times:
From what I understand, landing gear does not necessarily need to cycle all the way down before it goes back up. Hell, pilots can even lower the gear individually - main gear down, nose gear up, or nose gear down, main gear up, etc. I've seen photos and films of planes flying in the main-gear-down configuration, and always wondered why.
Boomer From United States of America, joined May 1999, 102 posts, RR: 0 Reply 2, posted (14 years 1 month 5 days 20 hours ago) and read 912 times:
Landing gear movement responds to the position of the cockpit control. If the landing gear is in transit and the lever in the cockpit is moved, the gear immediately stops and begins moving in response to the new commanded position. This is true in either direction.
I must beg to differ with the suggestion that landing gears are individually selectable. Generally, this is not the case. The DC10 and MD11 do have a switch on the copilot's side of the console that will 'lock out' the center main landing gear so that it will remain stowed when the other gear are lowered. This switch is helpful to maintenance personnel for such things as weighing the aircraft where you need to place the scales under the left, right, and nose gear. The center gear is not used as a weighment point and is left stowed. I know of no other aircraft that have a means for the crew to lower and raise only one gear at a time. In fact, maintenance personnel must install pins in the downlock assemblies to prevent gear from moving during testing when only one gear is to be cycled. This cannot be done from the cockpit.
I cannot explain how an aircraft is seen flying with the main gear down and the nose retracted, as Ilyushin96M describes, unless it is only a momentary observation. Nose landing gear units, due to their smaller mass, different aerodynamic loads, and smaller hydraulic actuators, usually cycle faster in either direction, up or down, than their main gear counterparts. This can lead to the impression that they are not operating at the same time. Any long duration nose up and main down operation is not a normal configuration and would be indicative of a problem.
Buff From Australia, joined Mar 2007, 0 posts, RR: 1 Reply 3, posted (14 years 1 month 5 days 7 hours ago) and read 889 times:
I cannot explain how an aircraft is seen flying with the main gear down and the nose retracted, as Ilyushin96M describes, unless it is only a momentary observation.
If the pilots or maintenance did not remove the "gear pins" on the mains, upon an "up" selection, the nose would retract and the mains would remain in place. Caveat - only on some aircraft.
It is important to know that there are many different sets of engineering designs on landing gear retraction/extension installations. Small twins tend to have electric, pneumatic or low pressure hydraulic systems, with some aircraft having a combination of multiple systems. Larger aircraft tend to utilize hydraulic actuators with electromagnetic sensors as feedback. Also on larger aircraft, not only the landing gear but the landing gear doors are involved. Watch a 747 takeoff and see how long it takes for the airplane to become clean - visually you will observe landing gear well doors open, a few seconds later the mains/nose will start to move to the retracted position, and not necessarily exactly symetrically, then the gear doors will close. The process can take as long as 20 - 30 seconds.
What's my point? The aircraft I have flown each had similar but different systems. On one type, mid-cycling of the gear handle could do major damage. On another, no damage. So the answer to Cricri's question, in my opinion, is that more information is required, as there is no simple answer.
As anyone who has read my previous posts will attest!
Jim From United States of America, joined Jul 1999, 455 posts, RR: 1 Reply 4, posted (14 years 1 month 5 days 5 hours ago) and read 888 times:
As one point of interest, the B727 has the capability (in fact in is the only way) to extend one gear at a time, IF IT IS DONE MANUALLY. Each gear strut has its own 'over center crank-pad' in the cockpit floor. If it is necessary to manually extend the gear, the flight engineer will use a 'speed handle' to turn the uplock hook, allowing the gear to free-fall.
A man on a crew I worked once got a nasty injury from that crank. A manual extention test was in progress in the hangar (the aircraft was on jacks, obviously) when someone turned on a the hydraulic jeep. As the gear handle was not in 'agreement' with the gear position, the gear was driven to match the handle, causing the crank to spin like a top. OWIE!