STEC55X advice - what can go wrong?

You need to be careful with how the S-TEC manual words this.

The S-TEC55X can NOT hold a specific pitch attitude, at least not one commanded. It CAN and does hold vertical speed.

What the CWS actually does is:

Flyingfish wrote:

and the autopilot roll and pitch servos will engage
and synchronize with the aircraft’s turn rate and vertical speed.

So the word ATTITUDE in the description is actually misleading.

When you release the CWS button, the AP holds the last recorded turn rate and the last recorded vertical speed. It will adjust the attitude of both roll and pitch accordingly.

Your procedure will not do what you expect, but it will do exactly the same as if you use whatever mode you wish for laterally and VS in vertical.

CWS is great for stuff like flying 360° until advised and changing altitudes while you do it, but it is NOT a CWS like you find them on Kings or Boeings.

What I use CWS for is just that: Say I am approaching a controlled airport and am told to VFR hold over a specific waypoint and a specific altitude: I press CWS, initiate the turn and fly to the specified altitude, then release the button and, if necessary, adjust VS to 0. What that will do is to fly 360° turns at the turn rate I had when I released the button and keep the VS I had or I selected. And that is about all the CWS will really do outside the normal modes.

The word attitude in the quoted paragraph is not appropriate in my view because it suggests that CWS will hold a specified attitude, which it does not.

Referring back to a discussion a couple of pages ago, today we used the go-around button on our Navajo for the first time from minima on an LPV approach to validate it (in VMC), and I have to say that it was perfect. It neatly pitched up to 10° and flew the centreline to the MAP, then straight on until SUSP was pressed, whereupon it flew the MA.

Very impressive for a ’60s design in a ’73 aircraft.

In my opinion, if you do not have a G/A button, fiddling with bugs and autopilot to initiate the go-around is not something you want to do at 200’ AGL while the nose is still pointing down. You would be better off disconnecting the autopilot, then pitch/power to initiate a climb, clean up and then turn the A/P back on in the desired modes.

What “fiddling with bugs” is necessary?

The action is to simultaneously apply power and press the button, which is on the left throttle.

I observe many go arounds as an instructor, and my experience is that many of them are messed up. The two most common mistakes are to fail to pitch (ie to apply power but continue to point at the ground) and to fail to raise gear or flap. Other lesser, but also important, things are not to open the cowl flaps and not to make the radio call.

Those are the errors of students and people revalidating, both of whom have put their minds to the likelihood of a go-around in the minutes prior to it happening.

My concern is that go arounds in real life in IMC are very rare. It takes an unusual set of circumstances: the METAR is both on minima and is slightly optimistic, otherwise either the approach is successful or not attempted. Go arounds for occupied runways are very rare in LVPs.

As real go arounds are rare (I had my first in five years a couple of weeks ago) they are unexpected and unfamiliar and I would imagine that the “fail rate” is even higher than in training or reval.

If that is the case, there must be an argument for doing them on automatics, thus freeing the pilot’s brain for getting as much right as possible, no?

Flyingfish wrote:

Then can we revert to THIS as a last resort:
1. Set G500 altitude bug
2. Put the AP in some horizontal NAV mode (HDG or NAV or GPSS).
3. Set climb power
4. Use pitch trim to point the nose up
5 Fine tune

1. Set G500 altitude bug
2. Set G500 IAS bug to Vy +5-10 kts or a predetermined cruise climb IAS.
3. Put AP in a usefull lateral mode
4. Set climb power
5. Set a corresponding VS, see how the speed develops and then adjust the VS so IAS stays on the IAS bug or above.
6. 500 ft before level off, reduce VS to 200 fpm and when aquiring altitude press ALT (if you don’t have an altitude capture device).

Vital is to keep IAS in your scan at all times. I say Vy plus 5-10 kts as a safety margin or a healthy cruise climb speed will do the trick as well. The moment IAS goes below the value you have set, reduce VS. Vy is well above Vs so this gives you a good margin.

What I do on my plane is to set VS to 500 fpm below 10’000 ft and to 300 above with constant monitoring. 500 fpm will usually result in a cruise climb speed of around 110 mph (Vy is around 90 mph and Vs a lot less than that) so a healthy margin. Clearly, when approaching the service ceiling, you will need to reduce further or quite possibly fly the last 2000 ft or so of the climb by hand. I’ve not taken my plane above FL150 since I have the AP and this procedure worked fine up to there. (ceiling is 17000 ft.

This works quite well but it is vital to remeber it is not a “set and forget” setting but you need to keep your scan up all the time. But generally, you should do this anyway whenever the AP is engaged or not.

I am sorry, I just noticed that I misread Aviathor’s post. He said if you don’t have a TOGA button, which I missed. Apologies.

Timothy wrote:

I am sorry, I just noticed that I misread Aviathor’s post. He said if you don’t have a TOGA button, which I missed. Apologies.

Yes, the Stec 55X does not have a GA button nor a GA mode. GA has to be flown manually by the book. That is one bit I do miss from the KFC150…

Flyingfish wrote:

nterestingly the bank rate is reasonable when the heading bug is close to the present course. So the workaround would be to
1. set the bug to present course
2. engage HDG mode
3. start twisting the knob in several small steps

The 55X is not known as a fantastic autopilot but the procedure you suggest is, in my opinion, the right way to engage heading mode in any aircraft. When you hit HDG, nothing should happen. Then turn the bug and the aircraft turns.

Essentially, your heading bug should always be sync’ed to your current heading. Engage heading mode then turn it.