Free and Correct
By SETH B. GOLBEY (From AOPA Pilot, August 1990.)
Every pre-takeoff check list contains an item that requires the pilot to determine that the movement of the flight controls in the cockpit corresponds to the correct movement of the control surfaces of the airplane. This follows an opportunity during the walkaround inspection to closely examine the condition and operation of the control surfaces. So why is it that a small number of airplanes is destroyed each year when pilots attempt to take off with controls that don't work properly? Surely this is one of the most preventable types of accidents imaginable.
Most accidents arising from misrigged or otherwise faulty controls occur just after major maintenance, like an annual inspection or major wing repair work. (Homebuilts also figure prominently in misrigging accidents.) If you own your own airplane, this can be taken into account. If you fly rental airplanes, or share an airplane with a number of others, it's safest to assume that everything will be wrong and proceed accordingly.
On February 21, a Piper Chieftain crashed and burned shortly after takeoff from Greeley, Colorado, seriously injuring the two aboard. Witnesses said that, just after liftoff, the airplane rolled steeply left, then right, before hitting the ground. The airplane had previously been involved in a hard landing that required removal and repair of the right aileron control system. The airplane was engaged in a post-maintenance test flight when the accident occurred.
Although the National Transportation Safety Board had not completed its investigation at press time, preliminary investigation revealed that the two right-wing aileron control cables were improperly connected to the aileron bellcrank. The aileron control system in the left wing had not been disassembled and remained properly connected. Misconnecting the system in one wing resulted in a loss of control because the left and right ailerons could only move in the same direction. If the control wheel were turned to the right, both ailerons moved down; if turned to the left, both moved up.
Investigators found that the airplane's service manual misidentified the aileron primary and balance cables in the left wing. An accompanying illustration mislabeled the control cables in the right wing. The installation discovered in the accident airplane corresponded to the erroneous schematic. The manual does, however, state, "Verify that the trailing edge of the left aileron moves up and the trading edge of the right aileron moves down when the control wheel is turned counterclockwise and vice versa when the control wheel is turned clockwise."
This accident is unusual (see "Retrospective," P. 119). We are more accustomed to hearing about controls that are rigged backwards the control input for a left roll results in a right roll, for example. Some quick-witted pilots have been able to recover from this situation and safely land the airplane.
The standard pretakeoff check is to determine that the controls are "free and correct," i.e., that they move freely and in the correct direction. Let's add one more item: Determine that the controls move to their full intended deflection.
On most airplanes, we can ascertain all three of these things on the walkaround. Before beginning the walkaround, we should remove any cockpit control locks. If the airplane you're flying uses external gust locks, remove them and stow them in a methodical manner so you don't overlook any. And don't forget that one way up at the top of the rudder.
As we visually examine the ailerons and elevator or stabilator, we can often see the movement of the control wheel or stick in the cabin; this provides a double check. We should examine the control surfaces' hinges for cleanliness and security. Usually, a single pin secures the two halves of the hinge. The pin usually has a bend at each end to keep it from falling out. If possible, move the pin within the hinge to check for binding, and watch the other end of the pin as you move it. If the other end of the pin doesn't move, the pin is broken within the hinge.
We should also examine each control surface's actuation mechanism. On some aircraft, this is a pair of cables attached to a bellcrank; on others, an actuator rod with a ball joint or bellcrank on the end. In any case, make sure there is no visible damage, that everything is properly lubricated, and that moving parts move freely. For controls that are mounted with bolts and nuts, make sure these are in good condition and that cotter pins and safety wires are in place.
We cannot see the portion of the control system that is hidden within the wings, tail, and fuselage, but the condition of the parts we can see is indicative of the condition of the parts we can't. On some airplanes, it is possible to remove a panel in the rear of the cabin and, with the aid of a flashlight, make a cursory examination of the cable or control rod runs to the tail. Make sure there's nothing rattling around back there that could bind the controls. Carefully inspect all openings around the horizontal and vertical stabilizers; there's no telling what might have crawled up your tailcone and died, and this is a favorite nesting site for birds. If you use blocks of foam or other plugs to prevent unwanted incursions, remember to remove and stow these, as they are quite capable of preventing proper control movement.
Everything that holds true of control surfaces also holds for flaps, trim tabs, and antiservo tabs. Check them carefully on walkaround as well.
During the pretakeoff check, take your time to make sure everything is working correctly. Make sure the controls are free and move to the intended limits of their travel. On some airplanes, the control wheel has such a small lock-to-lock distance of movement that any restriction to its freedom could have disastrous consequences.
Whether or not you were able to check correctness of movement during the walkaround, check again before takeoff. If you have trouble visualizing which way the ailerons should move when you move the wheel or stick, remember this rule of thumb. Grasp the wheel or stick (either hand will do). Extend your thumb vertically. Move the control full left or right. Your thumb is pointing at the raised aileron. Then move the wheel or stick all the way in the other direction and invoke the rule of thumb again. This second part is very important and could preclude an accident like the one described above. Never assume that because one aileron is doing what it's supposed to, that the other one is doing what it's supposed to. Check them both.
It is equally important to check the correctness of movement of the elevator or stabilator. A 15,000-hour-plus pilot told us that, until recently, he never checked the correctness of movement of his elevator. Until, that is, a friend was injured in an accident resulting from elevator control cables that had been hooked up backwards.
The rudder is seldom visible from the cockpit of a low-wing airplane, and this poses a problem. Particularly on airplanes in which the rudder and nosewheel are interconnected, it is difficult to check for free, correct, and full movement during the pretakeoff check. A careful preflight can ease your mind on this count, and you can sometimes check rudder deflection by watching its shadow on the ground.
Finally, while preparing for takeoff, make sure nothing in the cockpit will interfere with full deflection of the controls. This means check your yoke- or column-mounted clipboard to make sure it doesn't block aileron or elevator control. (On one recent trip, we found that a new clipboard we had just installed could get caught up on the number-two OBS knob when the yoke was in a certain position.) Make sure foreign objects haven't settled beneath the rudder pedals and that no loose items in the cockpit could end up there should they slide onto the floor or out from under a seat. Check your flap and/or landing gear handles, if the airplane is so equipped, to make sure nothing will restrict their movement. Trim controls should be similarly checked.
Headphone and portable intercom cables, particularly, can create a rat's nest that can easily get in your way at the worst possible moment. Many a pilot has experienced unnecessary excitement when a floor-mounted trim control has gobbled up a headset cable and tried to pull the headset right off the pilot's head. Needless to say, this can also destroy the cable or, worse, jam the trim system itself.
If the controls don't work as advertised, nothing else will either, and it's likely to be a very short flight. It only takes a minute to prevent an accident that, like running out of gas, has no excuse for taking place.