by Michael Kaufman, CFII
If you have not had the chance to read the article on autopilots in the June/July 2011 issue of Midwest Flyer Magazine, please do so as this is a continuation of that article (www.midwestflyer.com). Since writing that article, I have learned some new information and will be presenting the material here and in future issues on these topics: autopilot accidents, maintenance, autopilot glitches, GPS-steering (GPSS) and as mentioned, my favorite autopilot. Guess, I should say autopilots with an “S,” making it plural.
In the past 60 days, I have experienced a runaway trim in an A-36 Bonanza, learned of another runaway trim in an G-36 Bonanza, had a chance to learn about and fly the Garmin GFC-700 autopilot at Flight Safety, and became reacquainted with the Century 2000 autopilot in my flight student’s (George Luck) beautiful H-35 Bonanza.
I mentioned my favorite autopilots, and many of you may be considering purchasing one or doing an upgrade. As I said, there is more than one to be included in my list. The main consideration goes to the amount of money one is willing to spend.
My #1 choice goes to the Chelton AP-3C autopilot! The Chelton AP-3C is capable of GPS-V mode and will be covered in a later column. It is moderately priced @ $12,995.00 and will couple to the glide-slope while maintaining its GPS steering function (to be discussed in a later column), which is a real plus in autopilots!
After flying as pilot-in-command in George Luck’s H-35 Bonanza several weeks ago from Everett, Washington, IFR to McMinnville, Oregon, to tour the Evergreen Aviation Museum, I need to mention the Century 2000 as an excellent budget-priced autopilot. I also need to include the Garmin GFC-700 autopilot as the absolute, most featured autopilot I have ever flown, but it comes at a premium price tag. I will elaborate more on each of the units I just mentioned.
The Chelton AP-3C autopilot was a well-designed unit and was way ahead of its time. It has been discontinued after a merger between S-Tec and Chelton as the company was trying to promote the S-Tec 55X (also a good, but pricy autopilot). When a pilot is flying a coupled approach on most autopilots, it is necessary to switch the mode from the GPS steering mode (digital) to approach mode (analog) in order to capture the glide-slope. This is not true with the Chelton AP-3C autopilot, and this gives the pilot superior tracking of a GPS course while on LPV or any GPS approach with a glide-slope. When I check pilots in their aircraft, I like to explain how to do this and how to fly the approach correctly utilizing the autopilot. Seeing that very few pilots are flying this autopilot, the procedure they should use while doing GPS or ILS approaches are as follows:
Use your GPS steering function throughout the initial and intermediate portions of your approach on both ILS and GPS approaches. This includes published transitions and course reversals (both the procedure turn and holding pattern types). Once the aircraft is fully established on the final approach course, it is necessary to switch the autopilot to approach mode to get a glide-slope capture. Failure to do so will result in a well-flown approach, but the aircraft will not descend when the glide-slope needle centers.
The next autopilot to be discussed is the Century 2000. It is offered with or without a yaw damper and electric trim. The one I flew in George Luck’s H-35 Bonanza (a V-tail Bonanza) did not have either and did quite well on an IFR trip from Everett Paine Field, Washington to McMinnville, Oregon. When the autopilot is switched on, it goes to attitude mode or heading and altitude if they were selected before turning the unit on. This means it holds the aircraft in whatever attitude it is flying when you switch the unit on. The pilot then selects the heading and altitude mode, and the aircraft will fly the heading bug and hold whatever altitude is present when pushing the button.
Should you desire a change in altitude, pushing the UP/DOWN button, the altitude hold comes off and a change of one degree of pitch is made for each one second you press the specific button. There is no electric trim on George’s airplane, so a light and enunciator lets you know if the autopilot needs some trim help from the pilot. I prefer not having electric trim and had mine disconnected from the autopilot on my aircraft. George has the GPS steering option on his autopilot and like most add-on GPS steering modules, it works by having the autopilot in heading mode and selecting the module on a separate switch.
The Century 2000 can be programmed to fly a specific heading selected by the heading bug, and it automatically captures a course. This is done by pushing the heading and approach or nav-buttons simultaneously. If just the approach or nav-buttons are pressed, the aircraft will intercept the course at a 45-degree angle. The Century 2000 is a great autopilot at a low budget price.
The Garmin GFC-700 and 715 autopilots, when coupled to an air data computer and flight management system, do almost anything you could wish for except non-published holds. When ATC instructs you to cross a fix at a certain altitude, it can all be done on the autopilot. This is great for approaches and arrivals with multiple step-down fixes as well. As we pilots know, the higher the aircraft climbs at a specified rate, the slower the airspeed. These autopilots have the option of climbing at a specified airspeed, thus accepting a reduced rate of climb at higher altitudes. Altitude pre-select is a standard feature, and I will address this in a future article on autopilots.
It seems that any function one can desire of an autopilot, the Garmin GFC-700 can do except one that I found which can only be done with a Garmin 480/Apollo CNX80. This is holding at a non-published hold.
Example: “Cessna 2852F is cleared to hold 10 southwest of Kelsi on Victor 97, left turns, 4-mile legs, maintain 5,000.”
The only combination of navigator and autopilot that I have seen which can do this is the “480” and any autopilot with GPS-steering. The Garmin GFC-700 autopilot, as far as I know, is only available on new factory production aircraft.
Another item of major importance to pilots who fly autopilots are the “glitches” that occur from time to time. I would like to mention two specific ones before ending this column. One glitch I have seen on A-36 Bonanzas, came from the factory with this avionics package: King KFC150 autopilot, altitude pre-select, flight director and a Garmin 430 GPS navigator. This combination worked fine until the Garmin navigator was upgraded in the field to WAAS (Wide Area Augmentation System). So what is the glitch?
When the aircraft is being flown on autopilot on an ILS approach and the Garmin navigator switches from GPS to VLOC (VOR/Localizer) on the approach, the altitude hold will uncouple and the aircraft will climb to capture the glide-slope that is above the aircraft’s altitude. The result will be stalling the aircraft! I have intentionally done this in more than six different aircraft with this avionics package.
My second glitch is one many of us have heard about and trained for, but may have never seen. I now have seen it during a recent biennial flight review in an A-36 Bonanza. This is “runaway electric trim!”
The aircraft recently came from an annual inspection and during the flight with the autopilot in use, the electric trim decided to go wild. The autopilot was in altitude hold, and the autopilot servo decided to fight the trim until it could no longer win, resulting in the safety clutch slipping and disengaging the autopilot. When this happened, we went for an unexpected roller coaster ride. Natural pilot response, along with being in VFR weather, allowed this incident to have a safe ending. Look for a continuation of this autopilot discussion in future issues of Midwest Flyer Magazine. Until next time, remember; “The best safety device in an aircraft is a well-trained pilot!”
EDITOR’S NOTE: Michael “Mick” Kaufman is the manager for the Beechcraft Pilot Proficiency Program and a flight instructor operating out of Lone Rock (LNR) and Eagle River (EGV), Wisconsin. Kaufman was named “FAA’s Safety Team Representative of the Year for Wisconsin” in 2008.