MoA—”b”—In 1961 a mistrimmed stabilizer on a Boeing 707 caused the crash of an airplane. All on board died. The root cause was a malfunction in the electrical switch the pilot normally uses to electrically move the stabilizer. The switch stuck in an ON position and the motor moved the stabilizer to its most extreme position. The plane’s nose went up until it aerodynamically stalled. The pilots were unable to recover from the situation. The type of incident where an electric malfunction drives the stabilizer into an extreme position is since known as a ‘runaway stabilizer’.
To get a type rating for Boeing planes the pilots have to learn a special procedure to diagnose and correct a runaway stabilizer situation. The procedure is a so called ‘memory item’. The pilots must learn it by heart.