Autopilot—blessing or curse?

It can take care of flying tasks, freeing pilots to shift their focus to other items, such as writing down a clearance or inputting a flight plan into a GPS navigator or tablet. When it works properly and a pilot has thorough knowledge of its operation, an autopilot is a highly useful tool. In fact, at the airlines, inoperative autopilots are often a no-go item as they are required for flight in reduced vertical separation airspace from FL290 to FL410.

Automation accidents in aviation are more common than one might think, however. They are often fatal too. An underlying problem is pilots’ reliance on automation and unfamiliarity with the equipment and how it operates. Pilots should be extremely familiar with the system and know how to test it safely on the ground before taking off. This to confirm it does what it’s supposed to do and, perhaps most important, that you know all the ways to turn it off if it’s not doing what it’s supposed to do. My first airliner training for a 29-seat turboprop BAe Jetstream had us recite from memory the 12 ways to disengage the autopilot. Good advice that I won’t forget.

The number one culprit in automation accidents is the autopilot controlling the pitch-trim system. Imagine having an invisible hand moving the pitch trim without your knowledge. Pitch forces grow behind the scenes until the autopilot can’t hold it anymore. When it gives up, you’re stuck in a rodeo ride with a severely out-of-trim airplane. And usually the bigger the airplane, the harder the fall. Think of those two tragic Boeing 737 Max 8 crashes in 2018 and 2019 that killed 346 people and were the result of a runaway trim system. Newer autopilots have trim-in-motion warnings to alert pilots that something is not right. Those with older autopilots might want to rest their knee—or occasionally their hand—against the trim wheel for movement awareness. In light airplanes that are so equipped, I place a big red collar around the pitch-trim circuit breaker as a last line of defense to cut power to an errant pitch-trim servo.

Automation plays a role in light airplanes mishaps, too. A Beechcraft Baron pilot was cruising on autopilot at 8,000 feet when the airplane violently pitched down about 45 degrees “in an instant.” He rightly chopped the throttles to idle and disconnected the autopilot, but it took both arms to move the yoke aft. Once under control, he saw that there were seven units of nose-down trim input. Reducing the airspeed was critical in this case for regaining control of a severely out-of-trim condition.

The postmortem with the avionics shop revealed the pitch servo for the autopilot had a voltage fault causing a slow nose-down trim movement. The autopilot dutifully held altitude until it reached its load limit and handed off the airplane—with a built-in disaster—to the pilot. The older model autopilot only had a small, black needle in a not-too-obvious location to depict trim, with no light or aural warning. After the incident, the owner upgraded to a newer model.

In situations like the Baron incident and 737 Max crashes, controlling airspeed is critical. The higher the airspeed, the more power the trim has. An out-of-trim condition can effectively lock the controls at high speed. In the cases of the Max crashes, the airplanes were at such high airspeed, pitch control was essentially impossible as the airplanes were allowed to accelerate to and beyond the redline. The Baron pilot’s pulling the power to idle was critical to his survival.

Autopilots are a tool in a pilot’s chest. But do not rely on them. Hand-flying skills and a raised eyebrow of awareness are still essential to being a good pilot. Flight instructors half-jokingly like to say that students try to kill them multiple times a day, and the same could be said for autopilots, especially those that connect to the pitch trim. Know the system, keep an eye on its behavior, and, in the words of Ronald Reagan, “trust, but verify.” FT