AOPA's take on CWS

Guest Discussion
1

Saw this on AOPA’s web site - not much information but it describes a little bit about FAA’s objections to Control Wheel Steering (CWS); this may be the heart of the problems with the S-Tec 40x & 50x getting FAA certification?

AOPA questions FAA’s control-wheel autopilot controls policy

Feb. 22 — AOPA is opposing a proposed new FAA policy on autopilot controls. Concerned about pilots inadvertently engaging or disengaging the autopilot during critical phases of flight, FAA wants to remove or limit autopilot controls (sometimes called CWS — control wheel steering) on the control wheel.

But AOPA said that FAA has not published any “supporting human factors research or accident/incident reports” to justify the change. AOPA asked FAA to supply the data, and to allow more time for pilots to comment on the proposal.

“I’m concerned about single pilots operating in the IFR environment,” said AOPA President Phil Boyer. “We are constantly expressing concern about too much ‘heads down’ time. Using control wheel buttons cuts back substantially on looking down to activate an autopilot mode.”

Boyer pointed out that the military practice is to put multiple control buttons on the stick and throttle so that a pilot does not have to remove his hands from the primary flight controls to activate critical aircraft systems.

Steve

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The ironic bit is that the Cirrus planes cannot support CWS because the autopilot runs the regular trim in order to effect its commands. Most autopilot installations are rigged to “grab” the controls in whatever position they are in (and may run the trim, or ask you to do it, in order to reduce control forces.) CWS is all about grabbing and letting go of the controls, and the only way it could work in the Cirrus would be for you to position the controls the way you want them, let go of the CWS button, let go of the controls, and then hope you don’t go upside down while the autopilot starts cranking the trim to get you back to the attitude you selected.

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Steve:
Thanks for the heads up. It may be a situation of the FAA looking for a problem where none exists.

My understanding of the way that CWS works with the STEC is that the system will capture the rate of change of altitude or heading at the time the CWS is engaged and continue that rate. The system is rate based and not attitude based.

I think the concern is that a pilot may select CWS in a circumstance that is beyong the capability of the aircraft to preform. Say you engage CWS at 2500’ msl at a 1000 fpm climb straight ahead and then do nothing. At a certain point, the aircraft will no longer be able to climb at 1000 fpm regardless of how much up pitch is commanded and eventually the wing will stall. I don’t know if anybody ever got into trouble doing this. The AOPA news release suggests that the FAA has no accident data or human factors information to support the theory that it is a problem. I can’t see it being a problem. You put the aircraft in the attitude you want, hit CWS and the STEC will continue the same rate of change of altitude or heading that you had when engaged. You continue your scan and confirm that the system is doing what you want it to. If it does not, you hit the autopilot disengage, also on the control stick, and put the aircraft into the proper attitude and re-engage CWS.

I have heard that the concern extends beyond CWS to the altitude pre-select function as well. The concern is again that a pilot will select a rate of climb that the aircraft cannot do, and that the system will put the plane in a stalled attitude.

I recall reading on STEC’s website some while ago that there has never been an accident attritubatable to one of their autopilots. If this is so, apparantly that is not enough reassure some of these “were from the Government and we are here to help you” folks over at FAA.

I’m sure that AOPA would be pleased to hear from the Cirrus community, whether you are a member or not. I suspect that an overwhelming percentage of us are members. They exist to serve the members and make their member’s concerns known to the FAA and others.

Cirrus’s official position is that there are other autopilot suppliers out there, and that if there is a problem they can substitute another make. I don’t think this is too reasonable, since STEC has nearly all of the market. I think that the matter has to be worked out between STEC, the FAA, Cirrus AOPA and it’s members.

Finally, does anyone know whether CWS is enabled on the SR22’s that have been delivered to date? They appear to have the full STEC 55x system installed.

Saw this on AOPA’s web site - not much information but it describes a little bit about FAA’s objections to Control Wheel Steering (CWS); this may be the heart of the problems with the S-Tec 40x & 50x getting FAA certification?

AOPA questions FAA’s control-wheel autopilot controls policy

Feb. 22 — AOPA is opposing a proposed new FAA policy on autopilot controls. Concerned about pilots inadvertently engaging or disengaging the autopilot during critical phases of flight, FAA wants to remove or limit autopilot controls (sometimes called CWS — control wheel steering) on the control wheel.

But AOPA said that FAA has not published any “supporting human factors research or accident/incident reports” to justify the change. AOPA asked FAA to supply the data, and to allow more time for pilots to comment on the proposal.

“I’m concerned about single pilots operating in the IFR environment,” said AOPA President Phil Boyer. “We are constantly expressing concern about too much ‘heads down’ time. Using control wheel buttons cuts back substantially on looking down to activate an autopilot mode.”

Boyer pointed out that the military practice is to put multiple control buttons on the stick and throttle so that a pilot does not have to remove his hands from the primary flight controls to activate critical aircraft systems.

Steve

4

The ironic bit is that the Cirrus planes cannot support CWS because the autopilot runs the regular trim in order to effect its commands.

Actually the FAA objection is not to CSW it is to any autopilot controls on the control wheel. The Cirrus has the altitude hold and disconnect on the stick. The FAA claims that it is too easy for the pilot to unintentially disconnect the autopilot. The AOPA position is that the military puts lots of controls on the stick to allow the pilot to use them without having to remove his hands from the stick or looking down at the panel and the same benefits should be available to GA pilots.

5

Because I wince in expectation of the autopilot disconnect “sound” to put it nicely. If anyone accidentally turns off their AP and doesn’t know it, then I’d be surprised if they can hear at all…

And as for a sudden attitude change cause by AP disconnect as a problem. I can’t think of a situation where a pilot accidentally diconnects the AP and then can’t control the plane. Here I am in an 88 degree bank in a thunderstorm, let’s turn off the S-TEC…

And as for setting an AP to do something the plane can’t, like climb at 3000fpm all the way to 20K, well CWS has nothing really to do with that anymore than being able to dial in your altitude and VSI.

They’ll trust us with an NDB approach, but not with an AP?

Maybe there is more to this than I’ve read, but really… I think the FAA can trust us enough to put a few controls on the old yoke. When’s the last time someone went into a flat spin after using the ol’ PTT?

:slight_smile:

Dean

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disconnect “sound” to put it nicely. If anyone accidentally turns off their AP and doesn’t know it, then I’d be surprised if they can hear at all…

My club has a member who is deaf.

And as for a sudden attitude change cause by AP disconnect as a problem. I can’t think of a situation where a pilot accidentally diconnects the AP and then can’t control the plane.

I suspect they are less worried about a loss of control than they are about someone studying the approach plate thinking the autopilot is taking care of heading and altitude.

7

disconnect “sound” to put it nicely. If anyone accidentally turns off their AP and doesn’t know it, then I’d be surprised if they can hear at all…

I’ve flown a number of a/c and none so far has had an autopilot disengage tone of any kind.

From memory:

There was a famous airliner crash 20 or 30 years ago in the Florida Everglades. The crew selected gear-down and didn’t get a positive indication. The captain, I think, got up to go down below to verify that the gear was down and locked. When he got up, he knocked the control wheel, which disengaged the AP. Because it was the captian’s yoke, there was no AP-disengage warning. The logic was, I guess, that since the captain was normally the one to disengage the AP, the designers didn’t want to annoy the crew on this normal action. Otherwise, they’d start ignoring warning bells.

The a/c was trimmed well so nothing obvious happened. The a/c slowly descended and crashed. There were no survivors.

This shows the need to keep “flying the a/c” and not to be distracted from that task, even in an emergency (which the situation above wasn’t). But if the human factors inspired cockpit design had been different, the crash wouldn’t have happened. Of course, one can

always second-guess the cockpit design after a pilot error. And a different design which avoided this accident might have contributed to another which the extant design did not.

Perhaps the FAA is thinking back to this crash. They have a long memory for these things.

Robert Bedichek

PS. Ian Bentley from Cirrus guessed that SR22 #34 would be ready in May of 2001. Another datapoint for us Cirroproductionologists.

PPS. Has anyone noticed that I put a smiley-face on every post I make? It is pure manipulation. But it works, I haven’t been flamed once since I started doing this :-). Sheilds up :-).

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For more information about the accident to which Robert refers, see

http://www.aviationcrashes.com/special/eastern401.html

The NTSB accident records available online (Page not found) only go back to 1983, and so do not include the 1972 crash in question.

I must agree with AOPA that the FAA’s proposal seems to be without merit.

— Roger Freedman SR20 #266

From memory:

There was a famous airliner crash 20 or 30 years ago in the Florida Everglades. The crew selected gear-down and didn’t get a positive indication. The captain, I think, got up to go down below to verify that the gear was down and locked. When he got up, he knocked the control wheel, which disengaged the AP. Because it was the captian’s yoke, there was no AP-disengage warning. The logic was, I guess, that since the captain was normally the one to disengage the AP, the designers didn’t want to annoy the crew on this normal action. Otherwise, they’d start ignoring warning bells.

The a/c was trimmed well so nothing obvious happened. The a/c slowly descended and crashed. There were no survivors.

Robert Bedichek

9

I’ve flown a number of a/c and none so far has had an autopilot disengage tone of any kind.

Wow. Then you’ll be happy to know the STEC autopilots do.

Dean