What It Looks Like

An airplane's moving parts are subject to the greatest wear, and therefore should receive the closest scrutiny on the preflight inspection. The list includes the engine and its accessories, the propeller, wheels and tires, and the most important moving parts on the airplane -- the flight control surfaces.

When examining a control surface -- elevator or stabilator, ailerons, rudder, trim tabs, flaps, and spoilers if applicable -- pay special attention to the hinges that attach the surface to the airframe and allow it to move in response to control inputs.

One specialty hinge used on control surfaces is the piano hinge. So named, apparently, because they were first used on the long lid covering a piano keyboard, a piano hinge is also known as a continuous hinge because of its relatively long length compared to other types of hinges.

The piano hinge provides a strong and rigid means of attaching a control surface. The accompanying photo shows a piano hinge bridging a Piper stabilator and pitch trim tab. One side of the hinge is riveted to the leading edge of the trim tab, and the other to the trailing edge of the stabilator. A long hinge pin holds the two halves together. The pin is turned 90 degrees on each end to prevent it from working out of the hinge.

Several thousand hours of living in the harsh environment of slipstream and propwash eventually caused this piano hinge to wear. The result was some sloppiness in the trim tab and a mild case of vibration in flight. The problem was fixed by replacing the hinge with a new one.

During your preflight, test for hinge wear by trying to move control surfaces in all directions. Any sloppiness should be evident and is cause for further investigation by the maintenance shop. Also check for proper lubrication -- powdered graphite in the case of piano hinges.