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seat1a
Topic Author
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Joined: Mon Jan 11, 2010 7:52 pm

Landing Gear Deployed at Cruise

Thu Jun 02, 2022 9:04 pm

May be a dumb question, but a totally random thought: What would happen to say an A330 if the landing gear were deployed at cruise?
 
Avatar2go
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Joined: Thu Apr 14, 2022 3:41 am

Re: Landing Gear Deployed at Cruise

Thu Jun 02, 2022 10:27 pm

For Airbus aircraft, there are flight restrictions that prevent the computer from authorizing deployment of the gear in conditions that would damage the gear or airframe. If the pilots command gear down, the gear remain in place and the cockpit displays three red (or whatever the not-green indication is).

You may recall this was a factor in the recent Pakistan A320 crash. The pilots commanded gear down but the airspeed was too high, so the gear remained stowed. Then due to task saturation in a highly unstable approach, they touched down on the belly, then aborted and took off again, but the engines had sustained damage which shortly led to the crash.
 
e38
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Re: Landing Gear Deployed at Cruise

Fri Jun 03, 2022 2:21 am

seat1a, with regard to your question:

seat1a wrote:
What would happen to say an A330 if the landing gear were deployed at cruise?


Despite your example of an A330 and the answer above concerning automated features that would prevent such an occurrence, I perceive your question as "What would happen if the landing gear [of a large, or transport category aircraft] were deployed at cruise?"

Most pilots are aware that there may be a protective buffer between operational limits imposed by either the aircraft manufacturer or operator and the actual design limits of aircraft components and systems. Nevertheless, most responsible pilots would not intentionally violate an operational limit.

While I have not extended the landing gear above the specified limit--nor done so in the simulator--following would be my concerns, in order of severity:

1. Damage to, or separation of, landing gear doors.
2. Damage to hydraulic components and/or hydraulic systems.
3. Excessive vibration and/or airframe buffeting as well as considerable noise inside the aircraft.
4. Damage to the actual landing gear.

e38
 
RetiredWeasel
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Re: Landing Gear Deployed at Cruise

Fri Jun 03, 2022 10:55 pm

Gear extension and retraction speed limits are based on Indicated Air Speed (IAS) since that is representative of the aerodynamic forces on the airframe. For the 747-400 the speeds were 270 IAS. If flying at 35,000 feet (.80 mach..slower than normal), your indicated airspeed will be about 270. So extending the gear would probably not do any damage. Unwise and unusual, yes, as the aircraft would quickly lose airspeed since power available up there is not great. Just my humble assessment.
 
GalaxyFlyer
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Re: Landing Gear Deployed at Cruise

Fri Jun 03, 2022 11:45 pm

There’s usually a Mach limit or an altitude limit where the airspeed corresponds to a Mach number. It was M.60 for the C-5; IIRC M.80 for most Boeings.
 
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Starlionblue
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Re: Landing Gear Deployed at Cruise

Fri Jun 03, 2022 11:48 pm

As e38 says, there would likely be damage.

Avatar2go wrote:
For Airbus aircraft, there are flight restrictions that prevent the computer from authorizing deployment of the gear in conditions that would damage the gear or airframe. If the pilots command gear down, the gear remain in place and the cockpit displays three red (or whatever the not-green indication is).

You may recall this was a factor in the recent Pakistan A320 crash. The pilots commanded gear down but the airspeed was too high, so the gear remained stowed. Then due to task saturation in a highly unstable approach, they touched down on the belly, then aborted and took off again, but the engines had sustained damage which shortly led to the crash.


Gear extension at high speed is not only prevented by the LGCIUs (Landing Gear Control and Interface Units). It is also prevented by the closing of the safety valve at 280 knots, which isolates the gear from the hydraulic supply.

The indication you refer to would be three UNLK in red.


GalaxyFlyer wrote:
There’s usually a Mach limit or an altitude limit where the airspeed corresponds to a Mach number. It was M.60 for the C-5; IIRC M.80 for most Boeings.


250kt and Mach 0.55 on the A330. 200kt for gravity extension.
 
ReverseFlow
Posts: 392
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Re: Landing Gear Deployed at Cruise

Sat Jun 04, 2022 8:35 pm

IIRC abnormal gear extension during cruise is considered as catastrophic.

https://safetyfirst.airbus.com/control- ... nding/amp/

"VLO/MLO is determined to provide sufficient flight domain for landing gear extension/retraction, taking into account the structural limitation of the landing gear and landing gear doors."

Your doors will probably rip off. Not sure what the gear will do and it's probably not tested!
I did find a simpleflying article which mentioned a 727 where the gears extended and the doors ripped off.
I guess an asymmetric extension where one falls out in cruise might be worse?
 
Woodreau
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Re: Landing Gear Deployed at Cruise

Sat Jun 04, 2022 9:11 pm

Not an Airbus, but on a Canadair CRJ-700 an approach to one airport required crossing the final approach fix at 15,000ft in landing configuration. I vaguely remember the maximum altitude for landing gear deployment is 16,000ft. So there wasn’t a lot of altitude buffer for gear extension. You were either descending towards 15,000ft or level at 15,000ft when you crossed the FAF.

If you were level at 15,000ft and configured early while in the level segment, you found yourself at TOGA power with the gear down and the aircraft would not stay level at 15,000ft. It would start descending as soon as the gear was down.

So you held off configuration until just before the FAF, gear down and final flaps and started down the 4.8 degree glide path at the same time.
 
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VDemerest
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Re: Landing Gear Deployed at Cruise

Sun Jun 05, 2022 7:46 pm

With all of the penguins on here, it's gonna be hard to get you a good answer.

If you are flying at cruise altitude and at a high speed, you'll rip the gear doors off. Depending upon how the gear is designed to fall out of the well, you might rip the gear off as the hydraulic actuators begin to move the gear, or, the doors may not open up due to the air resistance. Hoot Gibson threw out the gear on his death spiraling 727-100 and ripped the doors off. The same thing happened to the China Airlines 'Test Pilots' in the SP.

Short answer: You'll rip the gear doors, struts, wheels and everything else off or damage them severely at high speeds - don't try it.

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