Cirrus Approaches and the S-TEC Autopilot

by HPA · March 10, 2012

Expect Vectors to Final, Part II

By Hank Gibson, Gold Seal, CFI, CFII, MEI

We talked last week about the Cirrus recommended procedure for briefing and flying instrument approaches. I hope you’ve had some time to practice some of the techniques presented there. If so, your approaches should look a lot more organized and streamlined! This week, we’re going to discuss what Cirrus recommends as far as using the S-TEC autopilot to fly approaches. I’m going to split the article up into how you would be flying the approach, either receiving vectors or flying directly to an initial approach fix. So, just turn that autopilot on, sit back and get ready to learn! (Note: All information below is taken from the Cirrus Flight Operations Manual for the SR20 and SR22).

S-TEC 55x Autopilot

Vectors

The autopilot procedure is pretty close to being the same for both non-precision and precision approaches. The exception comes when dealing with the descent on the final approach course (FAC). We’ll visit that a little bit later, though. For now, here’s how to program the autopilot when receiving vectors to the FAC.

Most of the time, when in a non-training environment (see: out in the real world), most pilots will be given vectors to fly to intercept final. Typically, it is faster to receive vectors then to fly the full procedure (especially on an ILS). Once ATC gives you that first heading to fly, set the heading bug for that heading first, then put the S-TEC autopilot in heading mode (HDG) and keep it in altitude mode (ALT).

Typical Vectors to Final

Now that the autopilot is on HDG mode, this would be the best time to go ahead and activate the approach on the Garmin 430 GPS. In doing this, it won’t mess up the airplane’s current direction of travel at all unless you change the heading bug. Referencing the above picture, the proper place to arm the NAV and APR modes would be when ATC gives you the heading to turn to in order to intercept the FAC. Also, don’t forget to change the HSI to VLOC on the Garmin 430.

Direct To An Initial Approach Fix (IAF)

The procedure for flying to an initial approach fix (IAF) is pretty simple and straight forward. The first step is to make sure that you have the proper fix loaded in the GPS. Keep the HSI in GPS mode and simply activate the approach. Then, make sure the S-TEC autopilot is in GPS Steer (GPSS) mode and it will fly directly to the fix to start the approach. Keep the autopilot on ALT or vertical speed (VS) and ALT as required.

The tricky portion is if you are doing a procedure turn. If your airplane is WAAS equipped, then you can leave the autopilot on GPSS mode. It will fly the hold following the Garmin 430. If it isn’t WAAS equipped, then you have to keep the autopilot on HDG mode. You will have to keep track of the legs and turn the heading bug to the proper heading at the proper time.

On the Final Approach Course (FAC)

Once you are on the final approach course (FAC) inbound to the final approach fix (FAF), this is when you want to make sure you have the NAV and APR modes active on the autopilot. For a precision approach, set the altitude bug for the DA so you’ll know how low you can go. As far as controlling the altitude, you can simply keep the autopilot in ALT mode and it will pick up the glide slope (GS) by itself. If the GS light is flashing on the autopilot, this means it is not active and has not captured the GS. Disengage the autopilot and try to set it up again. If it still doesn’t work, disconnect the autopilot and hand fly the approach.

On a non-precision approach, you are in charge of telling the airplane when to descend. A 500-800 foot per minute descent would be appropriate unless you have a very strong tailwind. In that case, you may need more like 1,000 fpm. Before you start the descent, set the heading bug for the MDA. Set the autopilot on VS and ALT modes so it will capture the MDA. It is a good practice to set the heading bug a 100 feet or so higher than the MDA so the autopilot won’t go through the altitude.

Once you have determined it is safe to land or it is time to execute the missed approach, disengage the autopilot. The Pilot’s Operating Handbook says you can keep the S-TEC autopilot on no lower than the DA or 100 feet below the MDA. After that, you are required to hand fly the airplane.

S-TEC Autopilot Limitations

There are a few limitations that pilots need to be aware of with the S-TEC autopilot. The first is it’s crosswind ability. There is a 12 knot maximum crosswind component between the FAF and the missed approach point (MAP). Any more than that and the autopilot doesn’t hold the course well at all. If the crosswind is between 12-17 knots, you are required to be at least 10 miles from the FAF when you intercept the FAC.

A few other limitations to mention are, if course deviation is greater than 50%, the autopilot must be disengaged. Flap deflection is limited to 50% with the autopilot. Intercept angles to intercept the FAC are limited to 45 degrees. And finally, when in moderate or severe turbulence, the autopilot must be disengaged. It just doesn’t handle it well.

Hopefully, this will help with your autopilot usage when flying approaches in a Cirrus. We’ve got one more thing to talk about and that is instrument failures in the Avidyne. Come back next week and we’ll discuss those.

How it Started

One of my best friends in high school, (Doug Gray) was a private pilot. He offered to take me up for a flight in a 1967 Cessna 150, N6228S. We took off from Calhoun, Georgia, and he took me on a scenic tour of the area, I was hooked. I later found out that my English teacher, (Jan Haluska) was also a flight instructor and the school was offering a ground school course the next year, which he taught, along with flight training with the goal of becoming a private pilot. I managed to talk my dad into funding the training, at the time the total cost was right around $500. Cessna 150 rental rates where $12 an hour, and the 172 we used for cross country was $15 an hour including fuel.

Training Begins

It started August of 1977. The fall semester rolls around, and I am enrolled in ground school, and if memory serves me, we met twice a week. First came the paperwork for my student pilot certificate, which at the time was included with the 3rd class medical. I loved ground school, especially learning navigation, plotting courses on the sectional, again this was before iPads and GPS, so we did a lot of dead reckoning and VOR navigation for cross countries. At the end of the course, I made an 83% on the Private Pilot written exam, remember this was before we had the question-and-answer books that on future test I would consume before taking a written.

2022.06.09 11.19 Flyhpa 62a27fea7716a

Flying

The fun really began on August 22, 1977, it was my first flight. To my surprise we used the same Cessna 150, N6228S that my friend Doug Gray had taken me for a ride in. The Cessna 150 had a standard VFR instrument panel, with one NAV/COM, and one VOR CDI. No intercom, so no headset, at the time I didn’t know what I was missing. I didn’t get my first headset until I started my instrument training in 2003. I was a big guy, I was 6’ 4” and weighed 245 lbs. but I do not remember being uncomfortable in the 150 even with the instructor in the right seat.

First flight lasted .8 hours, and we accomplished orentation, shallow turns, stability, and effects of flight controls. Over the next few months we added steep 720’s, slow flight, stalls, turns around a point, S-turns, emergencies, landings, (short field, soft field and normal).

Learning

At this point I want to talk about a training experience that still stands out. We were close to solo and were practicing takeoffs and landings. Turning base to final Jan got very upset at the way I was cross controlling the aircraft. Cross control is when you are in, say a left turn, and use opposite rudder to line the nose up with the runway. So, he had me depart the pattern and head east to the practice area, and climbing up to 5500 feet MSL, he had me slow down to just above stalling speed, start a left shallow turn and add right rudder. As the airplane stalled I had the strangest sensation, no roller coaster has ever come close, instead of blue sky in the windscreen I was looking at brown ground, and as far as I could tell we were upside down, through the terror of the moment Jan talked me out of the spin, controls neutral, oposite rudder, pull slowly out of the dive. As we leveled off he asked me what altitude we were at, as I remember it was around 2,800 feet MSL. Then he asked me what would happen if I experenced this on base to final in the traffic pattern. The answer was obvious, I would be a pile of wreckage off the end of the runway with a very short-lived aviation career. Needless to say this cured my cross-control tendencies.

Another training event the sticks out in my mind was the first time we did takeoffs and landings at the High School runway. The runway was 1,500 feet long, not sure of the width, but it seems like we had about 5 feet on each side of the wheels when on the center line of the runway. Landing from the south you also had to go between a cutout in the trees to be able to stop in time on the runway. After getting confortable landing here every runway since seemed huge. I remember landing at Chattanooga (KCHA) on a night cross country and commenting to Jan, that I felt like I could of landed sideways on the runway, it felt that large.

Very soon after this I started wearing old shirts to all my flight lessons, the reason for this occurred on February 8, 1978. The lesson that day was stalls, takeoffs and Landing. As we were taxing back in Jan told me it was time for my first solo. I was very excited, and after some last minute advice from Jan, including watch for floating on landing the plane will be light with him not in the right seat, complete 3 takeoffs and landings to a full stop. It was a blast, and at the end of my shirt was shorter in the back because Jan cut the tail out of it signed and dated my solo [an aviation tradition]. Total flight time accumulated on the day of my solo was 18.1 hours. I was now officially a pilot with solo priveleges.

In my next article I start cross country training, when Jan decided that it would be best accomplished this in the 172. Checking out in N5970R was like moving into a 747, this started a love affair with one of my faviriote planes to date. Since this time I have flown over 900 hours in many different models of the 172 and feel like I am stepping into an old friend every time.

More about Randy here: https://www.flyhpa.com/team/randy-delong/

 

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