Autopilot Autonomy

The airplane is finally ready for us to do our practice run. In this cold weather, the maintenance hangar has curtains across it in sections, so that the doors can be opened to admit and release aircraft without emptying the whole hangar of warm air. But our airplane is at the back, so this is a mass evacuation. All the airplanes are towed outside, one by one. There is some consternation when ours leaks a LOT of fluid as it is towed over the threshold of the hangar, but we then realize that the heater exhaust muffs must have been packed with snow when it was towed in, and the meltwater didn't drain out until now, when the airplane was tipped up slightly to go over the lip of the hangar. Last time I had fluid pour out of an airplane like that I had lost a fuel pump seal, but this is just water.

We install the tire valve cap and everything else checks out okay for the flight. I'll be in the back while my co-worker who hasn't flown for the longest will fly from the left seat, with the chief pilot in the right.

There's no cockpit door, but there are dividers behind the front seats, so I can't see what's going on in the front very well, just follow along through the checklist sequence and the taxi clearance. There's an extra headset plug back here, quite common in airplanes where there is not a third, observer seat in the cockpit, so I can hear the discussion up front, too. All equipment ground checks okay.

The chief pilot is familiar with local airspace, so gives directions to the training area as we depart VFR. We climb above the official training area, as it's a little too small for our speed, and then left seat engages the autopilot. The guy in the left is flying single pilot, so the conversation from the front lacks the crisp clarity of two crew SOPs so I have to guess a little what is going on. The airplane banks slightly left, and I see hands go to the autopilot roll control on the centre console and watch a steep left bank develop, before we roll level again.

"I'm in suspense back here," I say. "Please tell me you were turning the roll knob."

"We were," comes the response. "To the right."

Full right roll input on the autopilot produced a steep left bank. That would not be the mark of a properly-functioning autopilot.

"Does the altitude hold at least work?" I ask. When the airplane went in for autopilot repairs it could hold a heading slightly left of the selected one, and could keep its wings level, but would pitch up violently when the altitude hold was engaged.

They endeavour to keep the airplane right side up long enough to see if it can hold altitude. Are you familiar with the term 'homesick angel?' If this autopilot is emulating any specific pilot, it's an airsick student on his second or third lesson. (On the first lesson they usually don't get this violent, because they are afraid to break anything or make the airplane fall down).

They pull the circuit breaker on the autopilot and practice some airwork before returning for an ILS approach. The air was calm, the approach well-flown, and we got to look out the window at the chief pilot's home as we went by. On very short final the controller said calmly, "just to confirm you are cleared to land runway ..." and I forget which runway number it was, but I knew we already had a landing clearance, so I wasn't concerned. The people in the front suddenly realize, however, why the controller has made this assertion. They've been cleared for the practice ILS that is aligned with one runway, but cleared to land on another, diverging runway that starts with the same digit.

A little low level maneuvering later and we've landed on the correct runway, to taxi back to the maintenance hangar for more autopilot work. It's the airplane equivalent of the last moment lane change to make your exit. As we taxi in I text base: "Landed. Airplane still broken."

The return text comes after shut down, as we discover the gear doors don't stay closed after power is removed. "Old problems or new problems?"

"Both."

I leave to the chief pilot the task of itemizing them.

The weather, on the other hand, is absolutely glorious for flying. It's warmed up to barely below freezing and it's clear with very light wind.