Some more feedback, this from a 777/737 examiner. BA doesn’t have an SOP for CWS. It’s regarded as a degraded autopilot mode, and the preference is to disconnect.
With respect to using it in turbulence the preference is to switch the auto throttle to fixed thrust, the A/P will then bracket the speed and can deal with considerable turbulence.
With respect who sets A/P modes, in the 737 the pilot flying sets modes, in part because he ensures the aircraft is trimmed and there is no force on the control yoke.
I am sure many are familiar with the classic videos from the American Airlines Flight Academy. I was hoping the ‘Children of the Magenta’ might have mentioned CWS/TCS as part of managing automation, but haven’t spotted it.
from the STEC manual
CONTROL WHEEL STEERING (CWS)
Your new System 55 has a very desirable mode of operation – Control Wheel Steering
(CWS). This feature is the quickest way to engage both the Roll and Pitch Axes of the
System and synchronize the autopilot with the present aircraft attitude.
Depress and hold the Control Wheel Steering switch located on the aircraft’s control
wheel. The CWS and VS modes will annunciate and RDY will extinguish. Position the
aircraft in the desired roll and pitch attitude. Note: Aircraft vertical speed x 100 will be
displayed in the Programmer/Computer Annunciator window directly above the VS selector
knob. Example: + 6 equals 600 FPM rate of climb.
Allow the aircraft to stabilize in the desired attitude for 2 to 3 seconds, release the Control
Wheel Steering switch and the autopilot roll and pitch servos will engage synchronized
with the Aircraft’s turn rate and vertical speed.
NOTE: IF THE AIRCRAFT ROLL ANGLE IS GREATER THAN A STANDARD RATE
TURN WHEN THE CWS SWITCH IS RELEASED, THE BANK ANGLE WILL BE REDUCED
TO PRODUCE 90% OF A STANDARD RATE TURN AS A MAXIMUM.
From the CWS mode, the pilot may select other modes such as HDG, NAV, ALT or may
modify the present vertical speed using the VS knob.
The pilot may re-enter the CWS mode at any time by simply depressing the CWS switch
on the control wheel, positioning the aircraft in the desired roll and pitch attitude and
releasing the CWS switch. NOTE: After initial autopilot engagement when the CWS
switch is depressed, the roll and pitch servos will be disengaged during the maneuvering
phase. An audible tone will be heard indicating servo disengagement.
JasonC wrote:
If I flew more OCTA on autopilot I might well.
Only us Ozzies use the term OCTA!… OCAS in the UK…
I had to use it briefly this week after not touching it for a long time. For some reason (or rather no reason…), the autopilot attempted to capture the glide slope by climbing towards it. Which gives the passengers some kind of a rollercoaster ride and spoils the speed management. So I pressed it for a few seconds until we were on glideslope from where the autopilot did what it was supposed to do in the first place.
One update from a Boeing 738 captain – CWS is used in turbulence and is allowed by the company SOP. The pilot flying is responsible for setting the autopilot modes, the pilot not flying monitors.
Will continue to gather input from practitioners, but all airlines have different SOPs, and are constantly tweaking them, in some cases because they are discovering scenarios where the system is not reacting as they expected.
We Boeing flyers call CWS Airbus mode:)
In a 737 CWS mode is pretty much never used, it might be different for some airlines but the one I fly for, its not used.
CWS mode will automatically engage if pitch and roll modes are not selected
For example 737 will revert to level flight if you roll less the 6 degress. If you roll past that it will maintain that.
I guess CWS might have different operations in different aircraft
Flightsafety don’t teach use of it on the Mustang.
Their instructors for “my” C550/560 line suggest to use it under special circumstances only. For example when reacting to a TCAS/RA. Hold the TCS button, climb or descend according to the TCAS display and release the button when clear of conflict so that the aircraft can return to what it was doing before. One big advantage of using TCS instead of disengaging the autopilot for brief periods of manual flying is that the flight director will remain engaged. So in case of that TCAS event one can still follow the lateral guidance of the flight director. Similar for an emergency descent.
You mean that the roll servo in the Cirrus does not have the necessary clutches for CWS? I have to check how that works in the SR22.
