Continuously holding a heading and altitude on long trips in an aircraft without an autopilot, particularly during IMC, can be fatiguing. My first Bonanza did not have an autopilot, and that is one of the reasons the decision was made to sell the V tail and purchase the A36. It is expensive and cost ineffective to install an autopilot in an older airframe. Dollar-wise, it is almost always better to buy a plane with a panel that has already been updated by the previous owner.
An autopilot, nicknamed “George” by the aviation community, is a flight computer that in its most basic form, holds heading and altitude, avoiding task saturation for the pilot. This is especially helpful when flying single pilot IFR. Simply having the ability to keep the aircraft straight and level while opening up a chart, or reviewing an approach procedure, reduces pilot workload significantly.
Autopilots work by telling servos in the wing and tail how to position ailerons and elevators so that the desired flight profile is followed.
Most autopilots have four basic operating modes:
An “Altitude Hold Mode” that holds the aircraft’s specific altitude in spite of any updrafts or downdrafts encountered.
A “Heading Mode” that locks onto the selected heading bug on the compass portion of the Horizontal Situation Indicator, or HSI. This mode does not compensate for changes in wind at altitude.
A “Nav Mode”. This mode tracks a bearing to, or from, a selected ground based radio signal, or a GPS derived track. Once the A/P is locked on, the flight computer will continuously make any necessary minor corrections for wind to hold that specific track.
An “Approach Mode”. This is similar to the nav mode, only more sensitive. The approach mode is used to track an ILS localizer/glideslope, VOR radial or GPS approach with very tight tolerances.
My A36 came with the King KFC-150 autopilot/flight director with a KCS-55 Horizontal Situation Indicator, yaw damper and vertical speed selection. The HSI Compass System is electrically driven, making it immune from a vacuum system failure. Normally I don’t engage the autopilot until I am at least 1,000 AGL and established on departure. Like most things mechanical, they are not to be completely trusted, and that altitude buffer gives me a moment to scan the panel and ensure that the system is working properly.
My practice is to let the auto pilot fly precision approaches, like an ILS, and I hand-fly the non-precision approaches like VOR and GPS non-WAAS approaches.
The A/P system also has an optional altitude pre-select function, a King 297-B unit. The pre-select lets the pilot dial in the desired altitude, that when activated, instructs the aircraft to climb or descend at a specific rate. Once the desired altitude is reached, the unit chimes and the A/P will automatically capture and hold that altitude. Used correctly, the altitude pre-select can help the pilot avoid ATC deviations.
Another A/P option is the yaw damper. This keeps the aircraft stable in the lateral
longitudinal axis, reducing any side to side motion caused by turbulence. Rear cabin passengers really like
The KFC 150 A/P receives its roll and pitch information from the pressure-driven pump. Vacuum (pressure) pump health is critical to maintaining aircraft control while in the clouds, and they can fail at any time without warning. Determining a vacuum failure while IMC is tricky at best, and many pilots fail to keep the vacuum gauge in their scan. When a pump does fail, it can do so very slowly. If it happens in IMC, it can cause the pilot to follow a bad attitude indicator as it rolls over slowly, right into the ground.
Pilots should become familiar with how their autopilot system will react in case of a pump or HSI failure. In my aircraft, the HSI compass system is electrically driven, giving me more options if the vacuum pump fails. The heading system will still function and the correct response would be to turn on the Flight Director and engage the autopilot. The KFC 150 A/P will automatically hold “wings level” reducing the possibility of loss of control. Moving the heading bug will allow the pilot to make a turn or roll the aircraft in one direction or the other.
On later models, aircraft manufacturers like Beech installed a “Low Vacuum” warning light near the top of the glare shield, directly in the pilot’s line of sight. If the vacuum pump fails during instrument flight conditions, the master warning light will illuminate and an optional standby pump can be engaged by the pilot. This is much safer, and offers independent redundancy instead of relying on flying “needle, ball and airspeed” to maintain aircraft control.
Also, many aircraft owners who regularly fly in instrument conditions install a separate, independent backup system, an electric attitude indicator. This is used in the case of a primary pump failure. I installed the Castleberry electric backup attitude indicator shown here. It is a direct plug-in replacement for the traditional turn coordinator instrument and is permitted by FAA regs.
The key to being able to effectively use an aircraft for long distance travel, under varying weather conditions, is redundancy. Having these systems on board does not give me a feeling of invincibility, nor does it encourage me to tackle worse weather than I can handle. It does give me confidence that any one system failure is not an immediate threat to flight safety. Multiple system backups simply allow me more options to get down through the clouds safely.
Some pilots feel that an autopilot is a crutch for poor pilot skills, and that you are not a real pilot if you use an autopilot. Nothing could be further from the truth. Just ask the airlines, who have at least two pilots on board and regularly fly with the autopilot engaged.