Practical uses for CWS
 

I'm currently studying Autoflight and have come across CWS (Control Wheel Steering). On a standard flight from A to B when and why would it be used?

There is no use for CWS on a standard flight. I doubt there are any operators that ever use it.

SW

control wheel steering is the general mode of manual flying in the airbus

fly by wire family series as in the A300 its a choice..... im not sure if other

aircraft models are the same....:}

There´s no control wheels on FBW airbi and there are even less CWS, I´m afraid. Methinks questions refers to Boeing´s CWS which is almost completely different compared to Airboos FBW.

Normally never used.

Only conceivable uses:-

1. In turbulence mode, A/P reverts to CWS.
2. To increase bank angle in a hold when command mode doesn't give enough.
3. To increase pitch angle when command mode in V/S max cannot contain the airspeed.

It just provides stabilisation to manual flight. Same as airbus in 'manual'.

It's like having sex using a condom, I guess.

Some of our 747-200s are equipped with CWS. I've tried it a few times just to see what it could do. I was not impressed. There was a significant perceivable lag in control response, compared with manual flight. If the airplane trims up well, there is little use for CWS.

Flight with unreliable airspeed, you can use CWS to maintain the desired attitudes rather than doing it yourself

2 good uses for CWS,

in turbulance,

and for unrealible airspeed and/or altitude situations.

CWS and be used in the pitch mode or the hold mode or in both pitch and roll modes together.
Its a great thing, there to be used, if the situation warrents it.

no use! (after 5 years boeing)
only thing i like to do: off-set non-prec app using LNAV-VNAV:
disengage LNAV -> a/p reverts to CWS-roll: line up with centerline and keep vnav-FD-bar for vertical guidance.
but as i said: use of CWS is VERY limited.

CWS.
Useful in the L1011.
On all L10 aircraft (except those that were on the British register, or those that were used by GF) CWS can be selected on the ground, and is useful for low level turns immediately after takeoff, where maximum allowed bank angle is desired, due to noise abatement procedures, or obstacles in the takeoff flight path.
Very smooth operation on the 'ole Lockheed tri-motor.

Ummm....some rather interesting and wrong statements being made here!

airbond is on the money...

Boeings' recommended autopilot mode in severe turbulence is CWS when installed.

If you understood how it works compared to the autopilot, you would understand Boeings' FCTM statement.

...maybe get the books out guys and read a bit!

For what airplane is that "Boeing" recommendation? In what document?

How many of us have ever flown in severe turbulence? I haven't. I suspect more THINK they have, than actually have done so... Also, in 8+ years in the 747, I have had to disconnect the autopilot only once because it could not hold attitude in [moderate] turbulence.

B757 & B767 and as far as I am aware, all Boeing types that have CWS installed.

Direct quote from the FCTM - Flight Crew Training Manual.

...and that is exactly my point. Your autopilot (unless it was engaged in CWS) was not trying to maintain an "attitude" in the first place - it was trying to maintain a barometric pocket, ie: your altitude or flight level. In severe turbulence that is exactly what you want to try and avoid and why engaging CWS is so important as it will maintain an attitude instead.

Quite a lot of 757s/767s in operation have blanking plates over the CWS, not sure if that is a delivery option or not.

146

Well, I use it on the B737-NG for various purposes, often transitioning from raw data hand-flown to automatic flight, it allows me to select an autopilot and then programme the FDs (I could, of course, ask my co-pilot for the selections, but it's just a simple to do it oneself). Also, if hand-flying and needing a moment to check a chart, for example, or for flying visual circuits or circling approaches.

On light twins with more basic autopilots and flight directors, it's more useful, and has many purposes, but I guess the original question refers to 'heavy' aircraft.

Hi all,

I've been told that if you hold the yoke in a position for more than 2 seconds, CWS will switch in and automatically override the A/P until you disengage it.

Also, I know of specific CWS switches on the 73NG MCP, but how do you select it on the 744?

Brian

Useful in airliner-derivatives with split-axis autopilots during military AAR operations as it allows full manual control of the angle of bank and roll rate during turns on the AARA.

But more modern aircraft have smoother AFS response in HDG mode, so that is used by some operators - NAV mode giving little warning of the onset of a turn.

The A330MRTT may have a modified HDG mode to reduce rate of change of bank angle when entering the turn, approaching the desired bank angle, rolling out of the turn and approaching wings level again. This is intended to make the task of receiver pilots easier when remaining in contact on wing hoses in the turn.

In the VC10 tanker, we had the 'MAN' mode for the autopilot turn rate, this ensured that the pilot had direct control of the bank angle. But this feature wasn't fitted to later generation airliners - it being assumed that HDG or NAV would be sufficient.

CWS had it's uses in earlier generation aircraft such as the A300-B4, which did not have a Mach Hold. CWS was useful to periodically adjust pitch attitude to maintain the desired Mach Number.

Other than that, on more modern types with almost every mode controllable through a basic or more advanced mode, I can't think of much use for it. If I had it, (maybe I do) I doubt that I could think of much practical application for it.

Useful in it's time, a bit out-moded now :ok:

Regards,

Old Smokey

The B744 doesn't have CWS, neither do most 757/767 (it used to be a company option). Don't know about the 777 or the 717 but doubt it. So the only "modern" Boeing that has CWS is the 737. There you can override the AP and force it into CWS P or CWS R by applying a specific force to the control wheel. That way you can have the AP keep altitude and have manual control the roll axis (or vice versa).
Note, the B744 and the B757/767's with updated MCP's and AP's will hold current ATTitude if the AP is engaged with no F/D mode active (ie. both FD's off). As has been stated, FBW Airbi don't have CWS - the "manual control" is basically something like CWS but it doesn't hold pitch but vertical acceleration when the stick is centered.