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flybyguy
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Control Surface Tests Before Taxi

Tue Mar 15, 2005 1:05 pm

I've done control surface deflection tests on a Cessna, but what about large commercial aircraft where pilots don't have the luxury of being able to see anything more than their wingtips in the rear view?

I know that in glass cockpit aircraft there is a display that shows control surface deflections, however how reliable are these? Could there be an instance when testing things like ailerons, rudder and elevator show full deflections but in actuality the control surfaces are not functioning correctly?

Do you get tower or ground crew to observe the tests before departure?
"Are you a pretender... or a thoroughbred?!" - Professor Matt Miller
 
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Jetlagged
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RE: Control Surface Tests Before Taxi

Tue Mar 15, 2005 1:25 pm

Some large aircraft, like the 747-200, have a control position indicator which shows rudder, elevator, aileron and spoiler position. The 747-400 has this included on EICAS instead. The checklist response to one pilot moving his control during the full and free check would be in terms of how many pointers move up and how many move down (or left right for the rudder). E.g. "Two up, one down" for a wheel movement, checking the correct scheduling of the spoilers and ailerons. This is done while taxiing. If the aircraft has rudder pedal steering, the tiller has to be held neutral while rudder pedals are checked to avoid an S turn on the taxi way.

Surface position indication is as reliable as anything else on the panel. It's possible the indicator might show a false position, most likely not move at all. In that case it would undoubtedly have to be cross-checked by an external observer.

Most non-EFIS aircraft don't have surface position indicators. All they are doing is checking for full and free control movement, not checking the surfaces move too. The tower is not involved in anyway.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
KAUSpilot
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RE: Control Surface Tests Before Taxi

Tue Mar 15, 2005 1:57 pm

In the ERJ we simply check to make sure the control column moves freely and that nothing is jammed or hung-up. This is typically done as part of the before-takeoff checklist a few seconds before takeoff, however some captains choose to do it before leaving the gate as well.

There is no way to visually confirm that the surfaces are moving, and we don't even have surface position indicators on any of our displays.
 
CX Flyboy
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RE: Control Surface Tests Before Taxi

Tue Mar 15, 2005 2:07 pm

In many modern aircraft, as stated above, we have the ability to see an electronic representation of the actuator movements. It is unlikely that sensors will work together to show movement in different actuators when in fact the control surface is not moving. In some airliners, like the 777, we do not look at the flight controls synoptic when doing the control check. We move the controls to their full position and the computers and sensors will bring up an EICAS message if the control surface movement does not match the movement of our flight controls inside the cockpit. if this happens, we would likely return to the parking bay and have the engineers look at the problem. It is not good enough to visually check that there is movement of the flight controls by looking out a passenger window, ignore the EICAS message and depart.
 
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777wt
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RE: Control Surface Tests Before Taxi

Tue Mar 15, 2005 3:00 pm

On every AA flight I've been on, they deploy the spoilers to full then back to rest during taxi.
 
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Starlionblue
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RE: Control Surface Tests Before Taxi

Tue Mar 15, 2005 3:57 pm

Quoting 777WT (Reply 4):
On every AA flight I've been on, they deploy the spoilers to full then back to rest during taxi.

They don't actually use the spoiler lever for this. The spoilers act as augmentation for the ailerons, and extend when the yoke is rotated from side to side.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
aogdesk
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RE: Control Surface Tests Before Taxi

Tue Mar 15, 2005 4:56 pm

The flight desk indications of control surface movement are provided by feedback from the control surface actuators themselves. Linear and radial variable displacement transducers provide very accurate position indications, so the likelihood of erroneous indications is minimal. We never say never.
 
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HAWK21M
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RE: Control Surface Tests Before Taxi

Tue Mar 15, 2005 7:00 pm

Quoting Starlionblue (Reply 5):
They don't actually use the spoiler lever for this. The spoilers act as augmentation for the ailerons, and extend when the yoke is rotated from side to side.

Ditto

Also its mainly a Freedom of Mvmt kind of check involving Mainly the Primary & sometimes the secondary control surfaces.
regds
MEL
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Santhosh
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RE: Control Surface Tests Before Taxi

Tue Mar 15, 2005 10:14 pm

In the case of these non-EFIS aircrafts when there is a problem, can it only be know when the pilots feel difficulty in moving the control column? Or are there any other ways to rectify the problem?

Secondly what types of sensors are used in those aircrafts equipped with EFIS to monitor the actuator position?

Regards
George
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AvionicMech
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RE: Control Surface Tests Before Taxi

Tue Mar 15, 2005 11:55 pm

Quoting Santhosh (Reply 8):
Secondly what types of sensors are used in those aircrafts equipped with EFIS to monitor the actuator position?

As AOGdesk said in reply 6, LVDT's and RVDT's are used to sense the position of the control surface. Most of the time I believe these are the same sensors that are used for the autopilot system and the signal is also fed into the DFDAU to feed the FDR with the control surface positions as well as going into the Eicas computers on 757/767 and the DEU's on the 737NG to be shown on the screens in the flightdeck. This is from memory of when we removed the elevators from our 737's a few years ago so without looking it up in the Wiring Diagrams I cant be sure and am willing to be corrected but I am fairly certain.

Avionic Mech
 
B747FE
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RE: Control Surface Tests Before Taxi

Wed Mar 16, 2005 4:15 am

Quoting Jetlagged (Reply 1):
Some large aircraft, like the 747-200, have a control position indicator which shows rudder, elevator, aileron and spoiler position.

Flight Controls Position Indicator is the primary source during verification.
Even with that device, which only provide indication (747) for the outboard ailerons and spoilers No. 4 and 12, an always useful secondary indication can be seen on the four hydraulic system pressure gauges, cycling during the check.

Quoting Flybyguy (Thread starter):
Do you get tower or ground crew to observe the tests before departure?

Yes, if for whatever reason the indications aren't satisfactory the ground crew would go and take a look.

Regards,
B747FE.
"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
 
lowrider
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RE: Control Surface Tests Before Taxi

Wed Mar 16, 2005 5:57 am

The CRJ does have a "Flight Controls" page in the EICAS. Rudder, Ailerons, spoilers, and elevators get checked prior to each flight.
Proud OOTSK member
 
Yikes!
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RE: Control Surface Tests Before Taxi

Wed Mar 16, 2005 12:56 pm

As stated above, we rely upon the indications on the EICAS for control movement accuracy. The control column itself is not a good indication as it is laced with "artificial feel" by separate computers.

It is best though to do the aileron check AFTER flaps have been set for departure, NOT the way JAR operators do.

Talk about going back in time...
 
air2gxs
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RE: Control Surface Tests Before Taxi

Thu Mar 17, 2005 1:59 am

On the DC8 there is no primary surface position indicator except for the elevator (more on that later). The flight crew uses the hydraulic pressure indicator to check flight control actuator movement.

The pilot will call out a test position (i.e. left aileron) and move the applicable flight control, the FE will monitor the prssure gauge and report "drop, rise" indicating that the actuator moved (drop) and stopped moving (rise). They will repeat this for all three positions of the aileron and rudder (left, right neutral).

The elevator, not being hydraulically powered, is checked at 80 kts. The PF will push forward, pull back and neutralize while the NPF monitors the indicator. This indicator was added by AD in the '80s (I think).
 
MD11Engineer
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RE: Control Surface Tests Before Taxi

Thu Mar 17, 2005 2:17 am

MD-11 uses a synoptic image on the "config" systems display page. Essentially it is the aircraft displayed looking from the rear. A fully deflected control surface will give a green box.

Jan
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