What To Do
Autopilots are designed to be able to be pushed on a bit, but while you’re doing it, the automatic trim will be busy at work retrimming to try to win the battle with the human pushing—it doesn’t know you’re a human but thinks it’s fighting against flight loads. While you can overpower most autopilots, in the end you won’t win the war because you can’t overpower the trim once it gets to its limit. And then, if the autopilot does kick off, you’ll be left with an airplane that is borderline, if not completely unflyable, and who knows how fast or slow or at what angle of attack you’ll find yourself by then. So it’s important to respond quickly to keep things as well within limits as possible.
After you recover, at least with most light planes, you simply need to use the manual trim to set things straight. The Cessna 182, for instance, has a big, easily reachable trim wheel that many pilots use still even when their airplanes are equipped with electric trim. Even the big bad Cessna Caravan has a manual elevator trim wheel.
The Cirrus SR series airplanes, the SR22 and SR20, on the other hand, don’t have manual trim at all. In fact, like some other light planes, they don’t have aerodynamic trim. The trim switches activate a spring tension system. Essentially, the system is holding pressure on the control surface, and it’s possible still to have the trim malfunction, and the checklist is easy. It includes the admonition to pull the breakers, but if you fly a Cirrus (or any airplane with a trim breaker), figure out exactly which one/s they are.
Turning It Off!
We know that at the first hint that you don’t know what the autopilot is doing is, you need to turn it off, but in the case of Lion Air 610, it was clear the pilots were not up to that potentially lifesaving task. The good news is that the systems you fly are likely less complex and easier to manage than the one they found themselves fighting. Even so, you need to ask yourself, do you know how to do it?
There are usually several ways to accomplish this critical task, and they are specific to your plane. There’s the autopilot power button on the controller, the red “autopilot disconnect” switch on the yoke or stick, the circuit breaker and possibly the trim switches, too, which in planes with autopilots and autotrim are made to disconnect the flight control system. All can do the trick, if they’re functioning properly, that is. If one of those methods doesn’t work, try the next one. But disconnect it and stop it from trimming against you. Right away. If in the process you bust altitude, then plead your case with the controller or even file a NASA report. But don’t let the autotrim go to town on your airplane while you try to overpower it without turning it off, because that can be deadly.
In a story in Plane and Pilot more than a decade ago, our Peter Katz detailed an accident in a Beech 1900 twin turboprop commuter airliner in which the crew was on a repositioning flight just after maintenance and lost control of the plane shortly after takeoff from Barnstable Municipal Airport. It crashed into Cape Cod Bay, killing both pilots, who were the only occupants. The trim system had been installed incorrectly by the mechanics who had worked on it, the NTSB found, and the problem was exacerbated by an inaccurate drawing in the manufacturer’s maintenance manual that they might have referenced. Also, the crew, the report noted, failed to run the pre-takeoff checks of the trim system. Even with all that, had the pilots deactivated the trim at the first sign of trouble, they still might have been able to save the day.
What do you do if the plane you’re flying starts trimming itself? First, remember that this is a general discussion; you need to know your airplane’s specific POH procedures, know them by heart, practice them and be able to do them without having to think about it. This story won’t do that for you. You need to do it. Refer to your POH and ask an expert in your plane’s systems if need be. But get it done.
In case of a crisis, there are some actions the pilot in command needs to take. At the first sign of a failure, you need to act. Be sure to verify that a trim runaway is really what’s happening—quickly look for a movement of the indicator, which should take less than a second. Regardless, if in doubt, disconnect the trim as procedures stipulate for your plane. And remember that you need to account for the startle effect, eloquently described by many a pilot who’ve experienced an in-flight emergency and lived to tell about it as that one or two second yawning realization that something unexpected and possibly really unpleasant is happening.
More often than not, the cause of the problem isn’t the system at all but the pilot. It’s always a bad idea to try to hand-fly the plane while the autopilot is engaged, but it’s also a natural mistake to make. So unlearn it. Remember: Whenever you’re in doubt about what the autopilot is doing, disconnect it and hand-fly, something you should always be prepared to do during any phase of flight.
But, again, be prepared to retrim while you’re recovering. The pilots in the accident airplane in the Cape Cod crash, the NTSB said in its report, were struggling against an estimated 250 pounds of control force.
While trim runaways can be deadly, for some reason the FAA has traditionally not required multiple, redundant disconnect methods for the trim, although they do for an autopilot. For small Part 23 airplanes, there’s often only one way to stop a malfunctioning trim system: pulling the breaker. Turbine aircraft, in contrast, are generally outfitted with a split trim switch. The 1900D is so equipped. With such a switch, the pilot needs to activate both sides of the switch (which is actually two separate switches) at once for the trim to work. The benefit of this system is that in order to have a runaway trim, there would have to be two switches failing simultaneously, which reduces the likelihood of a runaway trim from low to extraordinarily improbable. It also allows the pilots to run a pre-takeoff check of the trim system to ensure that both sides of the switch are working as they should, including that the trim doesn’t run when only one side is activated.
For most of the rest of us, pulling the breaker is the solution. Do you know which breaker you’d need to pull in your plane? If not, figure it out. Many owners use a colored circuit breaker identification collar to ease the task, something we recommend.