737NG Ground spoiler deployment on landing
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From: A long way from home
737NG Ground spoiler deployment on landing
My understanding is that deployment is on compression of RG MLG WOW switch OR wheel speed greater than 60 knots and thrust levers at idle.
Had a guy trying to tell me that it also requires a rad alt less than 10 feet. Can't find any ref to that...can anyone clarify pls.
Had a guy trying to tell me that it also requires a rad alt less than 10 feet. Can't find any ref to that...can anyone clarify pls.
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From: I wouldn't know.
With a rad alt less than 10ft you can open the reversers (not a good idea while still in the air). Might have confused that with the ground spoiler thing.
Last edited by Denti; 20th September 2012 at 12:03.
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Had a guy trying to tell me that it also requires a rad alt less than 10 feet. Can't find any ref to that...can anyone clarify pls
Last edited by de facto; 20th September 2012 at 12:41.
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FCOM 9.20.15
Speed Brakes
Ground Operation
During landing, the auto speed brake system operates when these conditions
occur:
• SPEED BRAKE lever is in the ARMED position
• SPEED BRAKE ARMED light is illuminated
• radio altitude is less than 10 feet
• landing gear strut compresses on touchdown
Note: Compression of any landing gear strut enables the flight spoilers to
deploy. Compression of the right main landing gear strut enables the
ground spoilers to deploy.
• both thrust levers are retarded to IDLE
• main landing gear wheels spin up (more than 60 kts).
......
Ground Operation
During landing, the auto speed brake system operates when these conditions
occur:
• SPEED BRAKE lever is in the ARMED position
• SPEED BRAKE ARMED light is illuminated
• radio altitude is less than 10 feet
• landing gear strut compresses on touchdown
Note: Compression of any landing gear strut enables the flight spoilers to
deploy. Compression of the right main landing gear strut enables the
ground spoilers to deploy.
• both thrust levers are retarded to IDLE
• main landing gear wheels spin up (more than 60 kts).
......
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From: A long way from home
OK guys that's conclusive. So the next question is this (I'm not flying at the moment so I can't check it). Does the rad alt ever indicate over 10' when the main wheels are on the ground.
I guess this will depend on where the rad alt source is.... around the nose then it could do.... if its between the main wheels then it couldn't.
Reason for the questions is this.
When I first started flying the 737 I experienced a situation where the nose had been held off the ground for longer than the FCTM advises. Then (after a few seconds) the nose pitched up quite abruptly... subsequently told it was due to fwd movment of C of P as spoilers deployed. This could make sense if the rad alt was delaying spoiler operation for the first few seconds.... even though all other conditions for deployment had been met. Feasible?
I guess this will depend on where the rad alt source is.... around the nose then it could do.... if its between the main wheels then it couldn't.
Reason for the questions is this.
When I first started flying the 737 I experienced a situation where the nose had been held off the ground for longer than the FCTM advises. Then (after a few seconds) the nose pitched up quite abruptly... subsequently told it was due to fwd movment of C of P as spoilers deployed. This could make sense if the rad alt was delaying spoiler operation for the first few seconds.... even though all other conditions for deployment had been met. Feasible?
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I guess this will depend on where the rad alt source is.... around the nose then it could do.... if its between the main wheels then it couldn't.
The rad alt transmitters/receivers are on the bottom skin of the aircraft behind the nosewheel bay.
The rad alt is calibrated based on fuselage lengh and standard landing pitch angle to show 0 as the mainwheels touch...
About the rest no idea but i doubt a movement of the CP would cause such a pitch up,rather the result of the pilot pulling on the controls like an
Were you flying 700s? as im sure you would have touched the tail on 800s if such a high pitch delayed the spoilers.
Last edited by de facto; 21st September 2012 at 09:29.
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From: Grobelling through the murk to the sunshine above.
The radalt is supposed to be calibrated to read 0ft at touchdown, that is taking the flare angle into account. Obviously this must be slightly variable with flare, but to get it to read over 10ft would required a substantial nose-up attitude and you would be in serious risk of tailstrike.
The radalt antennae are just aft of the e&e bay door. Sorry but I don't know how to paste a picture in here!
The radalt antennae are just aft of the e&e bay door. Sorry but I don't know how to paste a picture in here!
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From: Chester
I do not know...or know any one who does know the answer to this.
Which rad alt display does the logic take as its source.... on the ground they display different values more often than not. Seem to remember in the AMS accident the no 1 rad alt failed and this caused auto land thrust lever retardation?
Which rad alt display does the logic take as its source.... on the ground they display different values more often than not. Seem to remember in the AMS accident the no 1 rad alt failed and this caused auto land thrust lever retardation?
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From: Australia
Which rad alt display does the logic take as its source.... on the ground they display different values more often than not.
The Flight Control Computers (A/B) get Rad Alt information from their onside Radio Altimeters. Irrespective of autopilot engagement, either Flight Control Computer can activate a relay in the autospeedbrake circuit when less than 10' is reached allowing the autospeedbrake lever actuator to move (if the other autospeedbrake conditions are satisfied).
What I don't know is if the FCC's talk to each other and come up with an average height of two Rad Alts or if each FCC uses only it's onside Rad Alt height for this particular function.
Rgds
NSEU
Last edited by NSEU; 7th October 2012 at 21:52.
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300-600 I do not know...or know any one who does know the answer to this.
Which rad alt display does the logic take as its source.... on the ground they display different values more often than not. Seem to remember in the AMS accident the no 1 rad alt failed and this caused auto land thrust lever retardation?
Which rad alt display does the logic take as its source.... on the ground they display different values more often than not. Seem to remember in the AMS accident the no 1 rad alt failed and this caused auto land thrust lever retardation?
What I don't know is if the FCC's talk to each other and come up with an average height of two Rad Alts or if each FCC uses only it's onside Rad Alt height for this particular function.
RA transmitter and receiver 1 is used by the FCC A and DEU1(capt DU) and RA xter/rcver 2 is used by FCCB and DEU2 (fo DU).
Last edited by de facto; 8th October 2012 at 14:16.
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From: Australia
Agreed, de facto, but spoiler control doesn't doesn't use the same kind of data as the DEUs. The FCC computes when the radio height is below 10' (using Rad Alt data) and generates a ground (earth) signal for the spoiler control relays.
The FCCs on most aircraft share data and can reject data if it disagrees, is out of tolerance, etc. FCCs can average, choose mid values (if there are 3 FCCs), and use other techniques if there are only 2 FCCs.
"Onside" = Left/1/A to Left/1/A, Right/2/B to Right/2/B, etc.
Rgds
NSEU
EDIT: For clarification, one Rad Alt "Transceiver" contains a transmitter and receiver. Only the transmit and receive antennas are individual units.
EDIT 2: Ref Boeing Wiring Schematic 27-62-11 Sheet 2
The FCCs on most aircraft share data and can reject data if it disagrees, is out of tolerance, etc. FCCs can average, choose mid values (if there are 3 FCCs), and use other techniques if there are only 2 FCCs.
"Onside" = Left/1/A to Left/1/A, Right/2/B to Right/2/B, etc.
Rgds
NSEU
EDIT: For clarification, one Rad Alt "Transceiver" contains a transmitter and receiver. Only the transmit and receive antennas are individual units.
EDIT 2: Ref Boeing Wiring Schematic 27-62-11 Sheet 2
Last edited by NSEU; 8th October 2012 at 21:26.
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Getting bit technical for me
I would GUESS that both FCCs must have the info of the RAD ALT<10ft to energise the speedbrake relays.
If one rad alt fails,the opposit side FCC must be used and I think the speedbrake will deploy with only one RA source.
I would GUESS that both FCCs must have the info of the RAD ALT<10ft to energise the speedbrake relays.
If one rad alt fails,the opposit side FCC must be used and I think the speedbrake will deploy with only one RA source.
Last edited by de facto; 9th October 2012 at 05:35.
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From: Next door
NSEU
Trying to get my head around this too!So if you have three FCCs (not sure if mine has two or three) and two rad alts it takes an average of the two rad alts. How would this be different from having two FCCs?
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From: Earth, where else?
Personally believe Airbus does it right on the A380...
With the side stick neutral during a take-roll with crosswind, the ailerons deflect in order to roll it into the wind. While accelerating down the runway, the beast rolls with up to 2degrees of bank into the wind, due to the aileron deflection. Spoilers do not come out, to avoid additional drag. Makes take-offs in 40kts crosswinds very easy!
With the side stick neutral during a take-roll with crosswind, the ailerons deflect in order to roll it into the wind. While accelerating down the runway, the beast rolls with up to 2degrees of bank into the wind, due to the aileron deflection. Spoilers do not come out, to avoid additional drag. Makes take-offs in 40kts crosswinds very easy!
