A340 Reverse before weight on wheels?
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A340 Reverse before weight on wheels?
I don't understand this pic. Is it possible to reverse a A340 before there is weight on wheels?
Engines reversing, but only few wheels on ground
Engines reversing, but only few wheels on ground
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I can't speak for the A340 itself, but I fly the A330 which I would imagine has the same procedures. On the the A330 when you acheive main landing gear touchdown (ie. the rear main wheels), you select reverse idle. Only when you have BOTH sets of mains on the ground do you select full reverse, if required. That's why you see the reversers deployed at such an early stage.
Hope that helps.
Hope that helps.
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As I understand it, yes! I remember reading about this a while ago (possibly here on PPrune).
There are a number of microswitches in the gear oleos which let the aircraft "know" when it is on the ground. i.e. select between 'ground' and 'air' mode.
For some aircraft (and those who fly them can fill in the gaps :-) reverse thrust can be deployed after x seconds when both mains are 'on' or 'y' seconds if one main + the nosewheel are 'on'.
Sorry I can't give a more technical answer, but this at least gives you an idea of how it works.
Regards,
Shuttlebus
P.S. Wasn't there an accident in the US with a DC-9 when an under-inflated nose oleo led to the aircraft (and crew) becoming confused - since some fuctions did not change over from 'ground' to 'air' (Probably an NTSB report)
There are a number of microswitches in the gear oleos which let the aircraft "know" when it is on the ground. i.e. select between 'ground' and 'air' mode.
For some aircraft (and those who fly them can fill in the gaps :-) reverse thrust can be deployed after x seconds when both mains are 'on' or 'y' seconds if one main + the nosewheel are 'on'.
Sorry I can't give a more technical answer, but this at least gives you an idea of how it works.
Regards,
Shuttlebus
P.S. Wasn't there an accident in the US with a DC-9 when an under-inflated nose oleo led to the aircraft (and crew) becoming confused - since some fuctions did not change over from 'ground' to 'air' (Probably an NTSB report)
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All planes I've flown, has to have the oleos compress some before the weight on wheels switches are activated. This is why the picture is bugging me, it must be different on the Airbus, as the oleos on this picture are not compressed at all.
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Please forgive the elementary nature of my suggestion, but maybe they bounced and consequently had compression of the oleos if only briefly? I admit that I cannot see any tyre smoke or other evidence proving my theory.
For that matter can you bounce an airbus or is the computer too smart for that?
For that matter can you bounce an airbus or is the computer too smart for that?
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Some more info (with sources :-)
From AAIB Bulletins (Feb 96) A340-311, G-VBUS
"... during takeoff is that the changeover between ground mode and flight mode takes place quite rapidly. In pitch, the flight mode is progressively blended in over a period of five seconds which starts when either the aircraft is above 100 feet radio altitude or it has been airborne for 5 seconds and the pitch attitude is above 8 degrees. However, the roll flight mode is blended in over a period of two seconds which begins 0.5 sec after the aircraft becomes airborne."
I can only assume that the changeover from flight mode to ground mode occurs below a given radio altitude and this allows the selection of reverse idle. (Similar to Scando's post above about the 737NG). On the A32x, the transition from Flight Mode to Flare Mode is initiated at 50 ft RA. (www.airbusdriver.net)
Regards,
Shuttlebus
From AAIB Bulletins (Feb 96) A340-311, G-VBUS
"... during takeoff is that the changeover between ground mode and flight mode takes place quite rapidly. In pitch, the flight mode is progressively blended in over a period of five seconds which starts when either the aircraft is above 100 feet radio altitude or it has been airborne for 5 seconds and the pitch attitude is above 8 degrees. However, the roll flight mode is blended in over a period of two seconds which begins 0.5 sec after the aircraft becomes airborne."
I can only assume that the changeover from flight mode to ground mode occurs below a given radio altitude and this allows the selection of reverse idle. (Similar to Scando's post above about the 737NG). On the A32x, the transition from Flight Mode to Flare Mode is initiated at 50 ft RA. (www.airbusdriver.net)
Regards,
Shuttlebus
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As far as I can remember, on the A330/340, the main wheel weight on wheels switches do not have to be "made" for reverse to be selected. I'm not even sure that they do on the 320 series. As I say - I am without FCOM at the moment so can't say for sure. The transition to ground mode starts at around 100ft RA dependent on type.
As regards bouncing - yes it's perfectly possible - I've done it!!!!!!! Oooops!!!!! On the bus, unlike other types, the spoilers will remain deployed during a bounce, unless either thrust lever is advanced. This does make for a firm second touchdown!!!! The 330/340 is very hard to bounce though - I did it on the the 320.
As regards bouncing - yes it's perfectly possible - I've done it!!!!!!! Oooops!!!!! On the bus, unlike other types, the spoilers will remain deployed during a bounce, unless either thrust lever is advanced. This does make for a firm second touchdown!!!! The 330/340 is very hard to bounce though - I did it on the the 320.
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If this aircraft is like a Boeing 747 or 767, it's not oleo compression which allows the reversers to be deployed, it's wheel bogey (truck) untilt. However, whether the bogeys on this type of aircraft have sufficient untilt to allow the reversers to operate, I can't say.
Rgds.
Q.
Rgds.
Q.
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Most aircraft use two out of three of Gear (WOW etc), Wheel Spin Up and Radio Altitude< 10 feet (or some value chosen in flight test) for both Spoiler Deploy and Thrust Reverser. Reason is that for a lot of aircraft WOW or ON GND (however detected) is often not set until after the lift is destroyed by the spoilers.
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Hi all,
Just consulted both sets of FCOM. BOTH 340 and 320 require's "on ground" sensing from at least one(of two) LGCIU (Landing Gear Control and Interface Unit) in conjunction with other selection inputs to allow reversers to deploy. Only reverse idle is available until all four blocker doors are fully open. Also on the 340 engines 1 & 4 have an interlock that prevents asymmetrical reverse thrust.
Hope this helps you all
Have a nice day
Just consulted both sets of FCOM. BOTH 340 and 320 require's "on ground" sensing from at least one(of two) LGCIU (Landing Gear Control and Interface Unit) in conjunction with other selection inputs to allow reversers to deploy. Only reverse idle is available until all four blocker doors are fully open. Also on the 340 engines 1 & 4 have an interlock that prevents asymmetrical reverse thrust.
Hope this helps you all
Have a nice day
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Justfor kix, Once one gets spin up from one set o wheels,this sends a signal to the sloilers to extend,thence the reversers to deploy!!Thats why we try to land on one set only...
If you don't get the spin up you have to rely on the Oleo squat ,which settles with a load of 2.5ton to activate the same sequence......
If you don't get the spin up you have to rely on the Oleo squat ,which settles with a load of 2.5ton to activate the same sequence......
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This discussion brings to mind an interesting event.
Some years back I was on the B747-200.
After a long cruise, when the a/c was pitched over for descent there was a 'kerrrrrchunk' sound from below us.
At the time it was noticed but since all seemed well we carried on regardless.
Later we got some strange indications from various systems, tending to lead us to believe the aircraft thought it was 'on ground'.
Nothing really serious, but maybe we were lucky it didn't depressurise!
It later transpired that the noise we heard was the nose gear sliding up it's oleo as the aircraft pitched down for descent, and jolting into the 'fully compressed' position. All oleo pressure had leaked away during cruise!
Maybe the reversers might have been active in flight! We didn't try that!
The nose wheel was pretty rough on touchdown.
Hope that helps some of you Whale drivers someday.
Some years back I was on the B747-200.
After a long cruise, when the a/c was pitched over for descent there was a 'kerrrrrchunk' sound from below us.
At the time it was noticed but since all seemed well we carried on regardless.
Later we got some strange indications from various systems, tending to lead us to believe the aircraft thought it was 'on ground'.
Nothing really serious, but maybe we were lucky it didn't depressurise!
It later transpired that the noise we heard was the nose gear sliding up it's oleo as the aircraft pitched down for descent, and jolting into the 'fully compressed' position. All oleo pressure had leaked away during cruise!
Maybe the reversers might have been active in flight! We didn't try that!
The nose wheel was pretty rough on touchdown.
Hope that helps some of you Whale drivers someday.
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340 Reverse
On the Airbus, reverser deployment occurs when either LGCIU senses L & R main gear 'on ground'. This occurs when the gear is not trailed and will occur when the sensor is detected as not being near, ( in proximity.) This would occur as soon as the in flight geometry of the landing gear is interrupted by the ground, i.e. back wheels in contact. Wheel speed is considered for ground spoiler extension and autobrake application only.
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Since we're on the subject of Airbus landing gear, there's an example of some of this in the foyer of the Science Museum in London, and an impressive lump of stuff it is too. However, there's a rather odd sticker on it with the word GROUND in big official letters and an arrow pointing to the, er, ground. I took a picture...
This amused me and my son on our recent visit, as we thought the a/c should have some more sophisticated and convenient indicators for which way was down. Or was it there to give the stowaways something to think about as they commenced their personal descent to the supermarket car park?
What is it there for? Is it some electrical connection point -- presumably the steel nipple on the handle -- for the bloke who scurries out and clips on the static discharge line? In that case, why not use the universal garden-rake symbol for electrical earth?
R
This amused me and my son on our recent visit, as we thought the a/c should have some more sophisticated and convenient indicators for which way was down. Or was it there to give the stowaways something to think about as they commenced their personal descent to the supermarket car park?
What is it there for? Is it some electrical connection point -- presumably the steel nipple on the handle -- for the bloke who scurries out and clips on the static discharge line? In that case, why not use the universal garden-rake symbol for electrical earth?
R
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Just finished looking at countless schematics and the FCOM. Jetboy has it correct main gear compressed from LGCIU and reverse selected from FADEC. Main gear compressed, which could come from Strut Compression or Bogie Tilt in this case (reverse) coming from Bogie Tilt according to my reading of the LGCIU schematic.
Yes the picture depicts a Brass ground point used for grounding static. I don't know why but most Aircraft types and people that I've encountered refer to ground as opposed to earth, I guess it's the American influence.
Yes the picture depicts a Brass ground point used for grounding static. I don't know why but most Aircraft types and people that I've encountered refer to ground as opposed to earth, I guess it's the American influence.
