Control Wheel Steering

[eeper]

An ex-737 skipper I flew with recently was talking about something on the 73 called control wheel steering. As far as I can make out it allows you to make inputs to the A/P with the yoke.

Can someone explain how this works and when (if ever) you would use it.

Cheers

[Intruder]

It's a relatively simple autopilot mode found in several military aircraft as well. When engaged, the autopilot holds the current attitude (generally, will go to wings level if less than 5 deg AOB). Use the yoke/stick to reset attitude, and the autopilot temporarily disengages while you have control pressure; when you release the yoke, the autopilot re-engages in the new attitude hold.

[GotTheTshirt]

CWS was on US aircraft but not on Uk aircraft (civil that is).
It works as stated but will maintain even constant bank angle or attitude. It is not considered a command mode ( like altitiude airspeed or heading modes) On the L1011 when then pilot is in a command mode but exerts a certain pressure on the controls the aircraft comes out of command mode with a partial disconnect and goes into CWS.
On the Eastern Everglade accident the aircraft was in altitude hold but went into cws when pressure was put on the yoke. The aircraft maintained a steady descent to the ground.

[Cornish Jack]

CWS (on the Tristar, at least) had one other advantage over the full autopilot mode - it had greater roll authority - (from memory) 35 degs as against 28 for the autopilot. This made it useful for holding in turbulence since it was also a command mode in pitch - Alt Hold was functional in both CWS and Command.

[The Flying Lad]

Sounds like Airbus Fly By Wire to a certain degree.

Cheers,

Justin

[How's it Hanging]

Sounds like TCS, (Touch Control Steering), that is in the DHC8. When the TCS button is depressed on the control wheel it uncouples the autopilot servos from the aircraft without disengaging the autopilot. When you let go it holds the current pitch attitude. Depending what vertical mode is engaged it is referenced to that, so it can be basic pitch, but more likely IAS, VS,or ALT. So if you want to change something without reaching for the AFCS controller you can TCS it. It also works if flying manually with flight director modes engaged. Instead of asking the non-flying pilot to increase rate of descent or change climb speed, you can hold the TCS button, change the attitude, let the button go and the FD now has new attitude. Another example of when you might use it is if an MDA is a 50'altitude, eg 850'. You would normally have the altitude preselect at 900', and once the altitude captures at 900', you then press the TCS, descend the aircraft to 850', let go and now 850' is maintained.
Many basic AFCS systems in light aircraft, like the King 150 (I think) also have a similar thing called "pitch sync" on the control wheel.

[Flap40]

One british type that has it, is the 146.

No doubt Raw Data will be along shortly to summarise! :D

[Pengineer]

All B737s with SP177 flight system (dual channel) have it, UK or US.

[Herod]

Flaps40. Correct me if I'm wrong, but isn't the 146 system pitch sync? CWS works in roll as well, at least on the 737-300.

[Flap40]

I'll have to dig the books out of the loft. It's three years since I flew it (and never used it anyway) so I could be wrong. :cool:

[alexban]

CWS-You're in control.When you release the control wheel,the AP mantains attitude.if the bank is less than 6 degrees it rolls back to level the wings.
you use this mode in severe turbulence,mainly

[Huck]

Th MD-11 has optional full-time CWS. All it does is hold pitch and roll if you let go of the controls. It is overridden by 3 pounds on the yoke in either direction.

Unfortunately, if installed, you cannot turn it off without killing the autothrottles or constantly holding in the thumb disconnect button. It makes the plane handfly like a pig on ice, due to constantly having to break that 3 pound threshhold to make any input. I hate it, and most carriers did not purchase it.

[Pointer]

Its called Touch control stearing in the Fokker50. when pressing the button the yoke you can give heading and roll inputs to the autopilot. dependant on what mode it currently is in; when releasing the button again it will go either to the previous heading it was on if released within 6 degrees of that heading or maintain current heading as per released. for the pitch mode it either returns straight and level or resumes in the pitch mode it is in with difference to heading in put, you can adjust the rate this way.

[A320 SFO]

We have this function on the A310 that i fly..absoloutly useless..never use the damn thing except in CMD, whereas the A320 uses it all the time FBW (fly by wire) ;)

[Wee Weasley Welshman]

Why use CWS in heavy turbulence on the 733? I think I can guess but am not sure.

Cheers,

WWW

[planedoc]

The Jetstream 31 has Touch Control Steering also. :p

[15/15 flex]

Don't know about the 73, but on the L1011 there was a TURB mode that effectively engaged the AP in CWS, but also fed inputs to the controls at half the rate demanded by the pilot.

Worked much better than CWS on the A310, as you could specify pitch or roll CWS, leaving the other in full CMD. The 310 is all CWS or all CMD.

[dolly737]

@WWW:
In fact, there are 2 separate CWS Modes: Pitch and Roll. During severe to extreme turb using CWS P prevents the A/P from chasing altitude and thus putting extra load on the structure. Also disengaging the A/T and manual setting of FMC recommended "Turbulence N1" will prevent A/T overreaction and result in a speed close to the Turb Speed of 280/.73 on the 733/4.

[Wee Weasley Welshman]

Ok thats pretty much what I was expecting. How are you selecting CWS Pitch - just nudging the control column or is there a more elegant way...?

WWW

[dolly737]

@WWW:
Well, I could write pages on the different ways to select CWS P...

You are right: nudging the yoke will "jump" the bird into CWS P. A more elegant way is to just deselect an active pitch mode (e.g. if you're in ALT HLD, pushing the ALT HLD button will deselect the mode and CWS P will engage) or you may, from the beginning, only select CWS on the A/P Engage Panel.