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Stealthz
Topic Author
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Asymetric Flap Deployment

Thu Mar 08, 2007 5:38 pm

I know modern aircraft have systems in place to prevent this and I would also hope that crews are trained how to deal with the unlikely event.
My question is .. what are the manifestions of such an event late in the approach, what would the aircraft be doing?

Cheers
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BAE146QT
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RE: Asymetric Flap Deployment

Thu Mar 08, 2007 6:10 pm

I hope I've interpreted your question correctly.

Simplistically, I would imagine that the wing with more flap would generate more drag and lift, causing yaw toward that wing, and roll away from it respectively. It would also have a lower stall speed than the other wing, which would have to be taken into account - especially if a go-around is performed and the asymmertic condition is uncorrectable.

Late in the approach, I expect it would be difficult to recover, though if it was *that* late in the approach, the flaps would likely be in landing configuration already and not moving, so this wouldn't be an issue.
Todos mis dominós son totalmente pegajosos
 
PhilSquares
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RE: Asymetric Flap Deployment

Thu Mar 08, 2007 6:31 pm

On the 744 there is asymmetry protection to ensure there is adequate lateral control. Since the protection is automatic you will not use alternate flaps. Here's the abnormal section from our QRH.

FLAPS DRIVE

Condition: One or more flap groups have failed to drive in the
secondary mode, or an asymmetry condition
detected.
Do not use alternate flaps.
[Asymmetry and uncommanded motion protection is not provided in
alternate mode.]
Do not use FMC fuel predictions with flaps extended.
LANDING PREPARATION:
GROUND PROXIMITY FLAP
OVERRIDE SWITCH . . . . . . . . . . . . . . . . . . . . . . . . . . OVRD
Use flaps 25 and VREF30 + 25 for landing (using flaps
primary or secondary).
If the amber minimum maneuvering speed band is above
the flap maneuvering speed:
AUTOTHROTTLE . . . . . . . . . . . . . . . . . . . .DISCONNECT
Use the displayed flap maneuvering speeds.
Do not accomplish the following checklist:
AIRSPEED LOW
If the inboard trailing edge flaps are affected:
CONTINUOUS IGNITION SWITCH . . . . . . . . . . . . . . . .ON
[Automatic continuous ignition may be inoperative. Provides
automatic approach idle.]


Not a real complex procedure, very straight forward.
Fly fast, live slow
 
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HAWK21M
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RE: Asymetric Flap Deployment

Thu Mar 08, 2007 8:31 pm

Beyond a Defned Assymetry.The Flaps will stop to limit the Assymetry to the Max permitted.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
CosmicCruiser
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RE: Asymetric Flap Deployment

Thu Mar 08, 2007 9:40 pm

Our first action is to return the flap handle to the last position of symmetry. Make it fly right then address the problem.
 
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fr8mech
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RE: Asymetric Flap Deployment

Thu Mar 08, 2007 9:45 pm

Quoting CosmicCruiser (Reply 4):
Our first action is to return the flap handle to the last position of symmetry. Make it fly right then address the problem.

Why would you attempt to move flaps that are assymetrical? You stand a good chance of making the problem worse. In fact, just about any system I've seen requires a reset of some sort before the flaps move again.
When seconds count, the police are minutes away, or may not come at all.
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Tristarsteve
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RE: Asymetric Flap Deployment

Thu Mar 08, 2007 9:59 pm

Flap assymetry is very serious, and all aircraft have a system to stop it.
A typical flap system has a motor in the wheel well driving torque tubes that run out each wing, with gearboxes that drive the flaps. At each wing tip is an assymetry detector. A transmitter counts the rotations, which are compared from one wing tip to the other. A difference of one rotation will cause the flap motor to stop, and brakes to come on on each wing tip. This can only be reset on the ground. There is usually a similar system in the slat drive.
The reason is that if one wings flaps continued to deploy, the aircraft would be uncontrollable. The flaps are much bigger than the ailerons.
The flap torque tubes turn about 400 revs to deploy the flaps. The crew get a warning of flap assymetry after ONE incorrect rev.

Many years ago I was working on a B737-200 D check. The flaps and flap housings had been removed and refitted, and an airtest was required. The pilots came back and reported they could not achieve the stall speed as one wing was dropping 10kts above it. We adjusted the flap drive one turn assymetrically, i.e. left wing up and right wing down. Next airtest perfect.

Just be glad the flap assymetry system works. The day it doesn't , it will kill you.

P.S. Philsquares is talking about the B744. This has inboard and outboard flaps driven by separate motors.
Also the B737 does not have slat assymetry protection, just a little plate of lights to tell you what went wrong.
 
DH106
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RE: Asymetric Flap Deployment

Thu Mar 08, 2007 10:37 pm

Kinda a follow on question - do DC-10s (& MD-11s ?) still have slats extended merely by hydraulic pressure, or was some kind of lock device fitted after the 1979 O'Hare accident (uncommanded asymmetric slat retraction following hydraulic pressure loss). Is it true that most other airliners use screw jacks which basically just freeze if power/hydraulic pressure is lost.
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
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SEPilot
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RE: Asymetric Flap Deployment

Thu Mar 08, 2007 10:47 pm

Quoting DH106 (Reply 7):
Kinda a follow on question - do DC-10s (& MD-11s ?) still have slats extended merely by hydraulic pressure, or was some kind of lock device fitted after the 1979 O'Hare accident (uncommanded asymmetric slat retraction following hydraulic pressure loss). Is it true that most other airliners use screw jacks which basically just freeze if power/hydraulic pressure is lost.

Do not know the answer to that for sure, but I believe that a mechanical latch was added to prevent this. What I do know was done was that the emergency manual was changed; it had directed the pilots to fly at minimum airspeed following an engine failure so as not to overstress anything, but if the AA crew had flown at normal go-around speed the left wing would not have stalled even with the retracted slats. The manual was changed to command normal speeds.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
CosmicCruiser
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Joined: Tue Feb 22, 2005 3:01 am

RE: Asymetric Flap Deployment

Thu Mar 08, 2007 11:12 pm

Quoting Fr8Mech (Reply 5):
Why would you attempt to move flaps that are assymetrical? You stand a good chance of making the problem worse. In fact, just about any system I've seen requires a reset of some sort before the flaps move again.

QRH states:
Place FLAP/SLAT handle to match flap position. Allow several seconds for system
response. If alert remains displayed, select the last symmetrical configuration.

You would have your hands full if you tried to fly around with them split or assym.

FLAP DISAG (CONFIG) - More than 4 degrees position difference between flap handle and outboard flap,
or more than 4 degrees position difference between L and R inboard flaps, or more than 4 degrees position
difference between L and R outboard flaps exists.
 
Tristarsteve
Posts: 3673
Joined: Tue Nov 22, 2005 11:04 pm

RE: Asymetric Flap Deployment

Thu Mar 08, 2007 11:13 pm

Quoting DH106 (Reply 7):
Is it true that most other airliners use screw jacks which basically just freeze if power/hydraulic pressure is lost.

Yes screwjacks seem to be the norm. They will not operate backwards, so even if the input shaft shears, they will stay still.
The B737 has hydraulic jacks, one to each slat. But when they are extended there is an internal locking mechanism that holds them in place, and needs hyd pressure to release it.
I never worked the DC10, but remember seeing that enormous steel cable that operated the slats. Must be 0.75in diam!

[Edited 2007-03-08 15:15:00]
 
DH106
Posts: 636
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RE: Asymetric Flap Deployment

Thu Mar 08, 2007 11:53 pm

Quoting TristarSteve (Reply 10):
I never worked the DC10, but remember seeing that enormous steel cable that operated the slats. Must be 0.75in diam!

Interesting - I had the impression the DC-10's slats were operated directly by jacks like the 737, but without the locks?
Cables of that thickness can't just be valve signaling cables - sounds like they're designed to take the slat loads. Perhaps the jacks are inboard somewhere and drive the cables.
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
TedTAce
Posts: 9098
Joined: Sun Mar 27, 2005 12:31 am

RE: Asymetric Flap Deployment

Fri Mar 09, 2007 12:43 am

Quoting TristarSteve (Reply 6):
The day it doesn't , it will kill you.

http://en.wikipedia.org/wiki/Jim_Bede#Bede_Aircraft

Quote:
Peregrine then redesigned the horizontal surfaces for a second prototype which crashed in August 1995 when one flap failed to deploy, killing the new company president, Joseph Henderson. That was enough to finally kill Peregrine.
This space intentionally left blank
 
N231YE
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RE: Asymetric Flap Deployment

Fri Mar 09, 2007 1:01 am

I once knew a flight instructor that experienced asymmetrical flap deployment on his C172.

As stated by such, asymmetrical flaps act like ailerons, and while he safely made an emergency landing, I would assume that the outcome of such an event on an airliner wouldn't be so nice.
 
Valcory
Posts: 88
Joined: Fri Dec 22, 2006 6:56 pm

RE: Asymetric Flap Deployment

Fri Mar 09, 2007 2:23 am

Quoting TristarSteve (Reply 6):
Also the B737 does not have slat assymetry protection, just a little plate of lights to tell you what went wrong.

Well depends on which B737 you are talking about .The B737NG is a little bit different.Trailing edge flaps asymmetry protection is provided in normal operation by the FSEU(Flap/Slat Electronic Unit) and TE Flap bypass valve. No asymmetry protection is provided during alternate flaps operation.When the FSEU detects a TE(trailing edge) asymmetry it sends a signal to the TE bypass valve to move to the bypass position. In the bypass position,the bypass valve prevents TE flap by hydraulic operation.
The FSEU compares the data from the left and right flap position transmitter to monitor the position of the LE flaps.If they are different by more than 9 resolver degrees there is an asymmetry condition.If the TE flaps are in an asymmetry condition,the FSEU sends electrical power to the bypass valve.This stops the hydraulic operation of the TE flaps(as mention above)
During an asymmetry condition the needles(needles split like 9 degrees) on the flap position indicator show the actual data from the flap position transmitter.After a flap asymmetry you must correct the the asymmetry to permit normal operation again.The asymmetry conditions resets when all of these conditions are true. The difference between left and right flap position transmitter is less than 7.5 degrees.The airplane is on the ground.Airspeed is less than 60 knots.
 
Ralgha
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RE: Asymetric Flap Deployment

Fri Mar 09, 2007 2:51 am

On the Brasilia, there are alternate flap controls that allow the pilots to move each pair of flaps independently of the others. They're only to be used if the asymmetry protections fail and there are problems controlling the airplane.
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
 
Tristarsteve
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RE: Asymetric Flap Deployment

Fri Mar 09, 2007 3:03 am

Quoting Valcory (Reply 14):
Quoting TristarSteve (Reply 6):
Also the B737 does not have slat assymetry protection, just a little plate of lights to tell you what went wrong.

Well depends on which B737 you are talking about .The B737NG is a little bit different.Trailing edge flaps asymmetry protection is provided in normal operation by the FSEU(Flap/Slat Electronic Unit) and TE Flap bypass valve. No asymmetry protection is provided during alternate flaps operation.When the FSEU detects a TE(trailing edge) asymmetry it sends a signal to the TE bypass valve to move to the bypass position. In the bypass position,the bypass valve prevents TE flap by hydraulic operation.
The FSEU compares the data from the left and right flap position transmitter to monitor the position of the LE flaps.If they are different by more than 9 resolver degrees there is an asymmetry condition.If the TE flaps are in an asymmetry condition,the FSEU sends electrical power to the bypass valve.This stops the hydraulic operation of the TE flaps(as mention above)
During an asymmetry condition the needles(needles split like 9 degrees) on the flap position indicator show the actual data from the flap position transmitter.After a flap asymmetry you must correct the the asymmetry to permit normal operation again.The asymmetry conditions resets when all of these conditions are true. The difference between left and right flap position transmitter is less than 7.5 degrees.The airplane is on the ground.Airspeed is less than 60 knots.

Sorry to be pedantic but I knew that. RTFQ. I was talking about SLATS.

The B737-200 was very simple. There was a flap posn transmitter on each wingtip that sent a signal to the flap posn gauge. In this gauge were two needles, one for left wing and one for right. If the needles separated, a switch in the gauge stopped the flaps. Too simple so they invented a FSEU!!

This system is no-go. One day we had a B737-200 stuck in KWI, and my mate had to run a wire from the wingtip to the wingbody fairing to get the flap system working again. Good CAA Desert procedure!, but it got it home.
 
Valcory
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Joined: Fri Dec 22, 2006 6:56 pm

RE: Asymetric Flap Deployment

Fri Mar 09, 2007 3:22 am

Quoting TristarSteve (Reply 16):
Sorry to be pedantic but I knew that. RTFQ. I was talking about SLATS.

I screw up i was thinking flaps anyway that's how the flaps system work
 
pilotaydin
Posts: 2100
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RE: Asymetric Flap Deployment

Fri Mar 09, 2007 3:47 am

if you suspect some sort of flap deployment issue, then you shouldn't deploy any flaps during a turn  Wink
The only time there is too much fuel onboard, is when you're on fire!
 
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fr8mech
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RE: Asymetric Flap Deployment

Fri Mar 09, 2007 5:43 am

Quoting CosmicCruiser (Reply 9):
QRH states:
Place FLAP/SLAT handle to match flap position. Allow several seconds for system
response. If alert remains displayed, select the last symmetrical configuration.

What type aircraft?

I know that on the Boeings I'm familiar with, all motion is stopped until the system is reset. Reset occurs through a breaker or switch actuation. At work tonight I'll look at the various AOM's and see what they say.

A true flap assymetry, not an indication problem, usually results from bad things happening in the system. Why push your luck and move those big air deflecting, drag inducing, lift inducing surfaces again if it didn't work out the 1st time?
When seconds count, the police are minutes away, or may not come at all.
It’s hard to win an argument with a smart person, but it’s damn near impossible to win an argument with a stupid person. ~B. Murray
Ego Bibere Capulus, Ut Aliis Sit Vivere
 
CosmicCruiser
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RE: Asymetric Flap Deployment

Fri Mar 09, 2007 6:26 am

Quoting Fr8mech (Reply 19):
What type aircraft?

MD-11
 
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fr8mech
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RE: Asymetric Flap Deployment

Sat Mar 10, 2007 3:57 am

Well, that may explain it. Strange flap system. If I remember I'll look at our AMM and AOM about it.
When seconds count, the police are minutes away, or may not come at all.
It’s hard to win an argument with a smart person, but it’s damn near impossible to win an argument with a stupid person. ~B. Murray
Ego Bibere Capulus, Ut Aliis Sit Vivere
 
Pope
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Joined: Thu Mar 24, 2005 5:57 am

RE: Asymetric Flap Deployment

Sat Mar 10, 2007 4:11 am

Quoting N231YE (Reply 13):
I once knew a flight instructor that experienced asymmetrical flap deployment on his C172.

As stated by such, asymmetrical flaps act like ailerons, and while he safely made an emergency landing, I would assume that the outcome of such an event on an airliner wouldn't be so nice.

My flight instructor would go ape shit when I deployed flaps while turning (either downwind to base or base to final) because of his fear of this. Though I think the possibility is remote, asymmetrical deployment in a single engine Cessna at approach sleep low to the ground would likely end in a loss of control event, stall and/or spin.
Hypocrisy. It's the new black for liberals.
 
ThirtyEcho
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RE: Asymetric Flap Deployment

Sat Mar 10, 2007 7:21 pm

"My flight instructor would go ape shit when I deployed flaps while turning..."


You have, there, a very good instructor. Assymetrical flaps could accentuate the turning force before you could react or send you into a sideslip with a flap down. An instructor of mine had a less polite way of saying it, "Never f**k with the flaps in a turn." He meant that you shoudn't be retracting flaps in a departure turn, either.

In general, if something goes wrong when you use a lever, button, switch, etc., put it back where it was before the bad thing happened.
 
Blackbird
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RE: Asymetric Flap Deployment

Sun Mar 11, 2007 8:19 am

Tristar Steve,

Why was Douglas so obsessed with Cables?
 
N231YE
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RE: Asymetric Flap Deployment

Sun Mar 11, 2007 8:29 am

Quoting Pope (Reply 22):
My flight instructor would go ape shit when I deployed flaps while turning (either downwind to base or base to final) because of his fear of this.



Quoting ThirtyEcho (Reply 23):
You have, there, a very good instructor.

Damn, I have had a few flight instructors, and not once have I ever been told not to deploy flaps while turning (which I realize, I have a habit of doing so. Well, I certainly learned something today, thanks you guys!
 
Tristarsteve
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Joined: Tue Nov 22, 2005 11:04 pm

RE: Asymetric Flap Deployment

Sun Mar 11, 2007 5:04 pm

Quoting Blackbird (Reply 24):
Why was Douglas so obsessed with Cables?

Sorry don't know. I never worked a Douglas aircraft.
But that slat cable was impressive. Never seen a cable on an aircraft approaching that size.
 
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HAWK21M
Posts: 30094
Joined: Fri Jan 05, 2001 10:05 pm

RE: Asymetric Flap Deployment

Mon Mar 12, 2007 11:22 am

Quoting TristarSteve (Reply 16):
This system is no-go. One day we had a B737-200 stuck in KWI, and my mate had to run a wire from the wingtip to the wingbody fairing to get the flap system working again. Good CAA Desert procedure!, but it got it home

The Inbd Aft TE Flap cable of the Load relief is another tough routing  Smile

regds
MEL
I may not win often, but I damn well never lose!!! ;)

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