There are some in-flight failures that are extremely difficult, if not impossible, to recover from. One such malfunction is the failure of a major control surface. A positive control check is part of the preflight procedures section of the practical test standards for gliders since they are often assembled right before the flight. While a positive control check may not be warranted for each flight in certified airplanes, it’s definitely worth doing every time there has been any type of maintenance done to the airplane or if you’re flying an airplane that is not yours.
Two people are required to conduct a positive control check. One person moves around the outside of the airplane and stops at each control surface to hold it steady while the person inside the cockpit moves the control actuator that manipulates that particular surface. Make sure that the actuator won’t move when pressure is applied while the person outside holds the control surface steady. Also, when the person outside relieves the pressure (still holding for resistance), check that the control surface moves in the appropriate direction with each control input. This ensures that all the linkages are properly connected before you start taxiing out for departure.
You may think this check can be completed in the runup area as part of the control check during the runup. But the runup control check is not fail-proof. A pilot who flew a Piper Cub that was assembled on site at this year’s AirVenture was forced to climb from the rear seat to the front seat to move the CG forward enough to level off his airplane after he realized that his control stick wouldn’t move the elevator down. Only the linkage that brought the elevator up was connected. He performed a control check in the runup area, but didn’t realize gravity brought the elevator down – not the control stick. Fortunately he landed safely in the end, but the type of CG manipulation the pilot accomplished would be impossible in most airplanes and such a control failure would generally not have a happy outcome.