Flight Controls Check

[LEM]

Here (737 classic, but this should apply to all airplanes, I guess), nobody seems to realize the need to check that the flight controls return freely to (almost) center when released.

The Boeing manual says clearly: "Verify full travel, freedom of movement, and controls return to center."

So, how do you perform this check while taxiing out?
Do you turn, let it go, push, let it go, pull, let it go........

or simply turn, push, pull and that's it? :E

[captain_josh18]

hey, correct me if im wrong... but ive seen the control surfaces moving before pushback, which to me seems that they do the control checks before start.

just a guess! :)

[Genghis the Engineer]

(737 classic, but this should apply to all airplanes, I guess),

Nope, it should apply to all aeroplanes with irreversible controls.

A great many aeroplanes with reversible controls will not self-centre without flying speed, nor should you expect them to.

Having said that, this really applies only to the smaller aeroplanes that I work with (up to Islander size mostly), I believe that the last airliner build with reversible controls was the Comet IV.

By reversible, I mean that without power, applying a load to the control surface will also move the inceptor. By irreversible, I mean that any such feedback is non-existent or artificial.

Presumably any large aircraft doing control checks before main engine start has either ground hydraulic power or (more likely) a running APU driving the hydraulics and electrics (pretty much essential I'd have thought since you'd want power to the ground steering and brakes wouldn't you?).

G

[safetypee]

G the last airliner? …. you of course forgot the 146/RJ (it qualifies as ‘big’ in my book), it has servo tab controls that meet your definition. The control surfaces are free to move (windy day), but if the servo tab limit is encountered then the servo tab moves which in turn moves control column. The 146/RJ controls do not re-centre and the control column drifts about a central position depending the trim setting, elevator balance wt, and wind strength; thus the column has a restraint.

On most aircraft and especially those with reversible controls is desirable (possibly a requirement) to conduct the control check as late as possible before take off. This is to ensure that the probability values are met for a jammed control occurring during take off. For servo tabs, the check should be done into wind enabling the surfaces to ‘fly’.

There was a notable event when a preceding departing aircraft’s jet exhaust threw a stone into the elevator of a MD 80 (servo tab) lining up close behind, which caused a control jam. Other events have resulted from snow / ice problems where the control check was not included with the ‘clean aircraft’ check.

[Oktas8]

On most aircraft and especially those with reversible controls is desirable (possibly a requirement) to conduct the control check as late as possible before take off.

Safetypee do you have a reference for this, either in national regulations or a manufacturer's manual?

Not doubting, just wanting to find out more.

O8

[80/20]

Good questions – as usual LEM!

When?
Boeing: During taxi when conduction the ”Before Takeoff Procedure”
Some other airlines: After engines started before taxi

How?
Boeing: Displace rudder pedals, control wheel and control column in both directions. Verify full travel, freedom of movement and controls return to center. Hold nose wheel steering wheel during rudder check to prevent nose wheel movement.

Some airline manuals also say: Move all flight controls through the full travel to ensure they operate freely. When making flight controls check slowly move all flight controls to the stop, do not slam.

Simply turn, push, pull and that's it?
I see some do it in one continuous movement through all quadrants while others go through centering several times. Boeing does not see the need to emphasize this in Pilot Manuals, Maintenance Manuals or during the Boeing Factory Pilot Courses.
Anyone else found some wise reason for a specific technique here?

[quid]

80/20-

On the DC-8 we have some very specific systems reasons for doing the flight control checks a certain way.

[Genghis the Engineer]

Thanks for that Safeteypee, I stand corrected. I confess that I've never had any encounter, either professionally or as a pax in a 146/RJ.

Incidentally just before I defected from military aviation to a life of better-paid sin in civil aviation we had a nasty in (I think from memory) a Jaguar (1996?), where controls full and free were done - the stick moved, but the ailerons and tailplane didn't - something missed because checks at the time didn't include visual confirmation. They did shortly afterwards, and I imagine still do.

Which is an interesting question for the bus drivers - when you do your control checks, do you really confirm that the rudder and elevator move? For that matter in how many types can't you see the ailerons / spoilers / flaperons from the cockpit?

And before anybody says that's ground crews job to get right, does anybody know an organisation with more professional ground crew than the RAF? - and they got it wrong on that occasion.

G

[exeng]

do you really confirm that the rudder and elevator move? For that matter in how many types can't you see the ailerons / spoilers / flaperons from the cockpit?

Some airliners have control position indicators, i.e. A320, B747, B777. Some do not, i.e B737 where you can see the ailerons move but certainly cannot see the elevator or rudder!

A large Austaralian carrier I was seconded to in the 1980's required the Flight crew to carry out a complete visual flight control check whenever any flying control system had been disturbed in maintenance. This was of course in addition to the normal duplicate inspections by LAE's. It took about 5 mins with the F/E observing outside whilst the pilots did the wiggling; I thought that was 5 minutes well spent.

For normal line ops on A/C such as the B737 I do believe it is reasonably safe to assume that if the previous flight was normal ,then with a full and free check of controls, it is safe to assume that the 'invisible' surfaces are actually moving as intended.


Regards
Exeng

[80/20]

The Flight Control Surface Position Indicator option is actually available for the 737NG.
It can be selected by the MFD to be displayed on the lower DU - it indicates ailerons, elevator, ruddder and flt. spoilers position with top and bottom marks to show fully deployed/max travel - really nice!

[80/20]

It is an available option that may be ordered. If you have it (don't sound like you have it since you haven't seen it) you simply push the MFD button until it is displayed on the lower DU. The function is described at the end of Section 10 in Chapter 9 - Flight Controls in the B737 OPS Manual Vol 2 in TBC manuals and customized manuals for operators that have purchased this option.

[Blacksheep]

For those wondering about whether or not the surfaces actually move or not, on the B737 (and other types) if any surface failed to move, follow up would not occur and the control check would not be 'full and free' - the controls would feel very heavy in the applicable direction and would not self centre. Just try moving the controls without hydraulic power applied to see the effect. That's why it is so important to ensure that the controls return to centre by themselves - failure to do so is an indication of possible control surface failure.

[safetypee]

Oktas8, sorry there’s no definitive requirement. JAR 25-671 requires:-
Probable malfunctions (a definition of risk frequency) must have only minor effects (a definition of risk) on control system operation and must be capable of being readily counteracted by the pilot. i.e. Any jam in a control position normally encountered during take-off, climb, cruise, normal turns, descent and landing unless the jam is shown to be extremely improbable (another, yet more severe definition of risk frequency).

Thus whatever certification basis the manufacturer used, which usually involves a time of exposure to the risk of a jam (stone in the controls pre takeoff), may only be reflected by an innocuous statement in the crew operating manual. So check controls just before takeoff is actually a very important requirement for the particular aircraft type.