A pilot observes fluctuating airspeed indicator with no configuration changes.

• A. Elevator System Jammed
• B. Rudder System Jammed
• C. Stabilizer Trim Runaway
• D. Unreliable Airspeed

Answer: (D)

When the airspeed indicator fluctuates without any change in the aircraft’s configuration, the most likely issue is an air data system fault rather than a mechanical problem with the flight controls. The airspeed indicator relies on the pitot-static system to sense dynamic pressure. If the pitot tube is blocked, the static ports are leaking, or the air data sensor itself is failing, the readings can wander or alternate erratically. In such a case you can’t trust the airspeed indication, so the indication is labeled unreliable airspeed.

That’s why the other possibilities don’t fit as well. An elevator jam would primarily affect pitch and flight attitude, and you’d notice abnormal nose-up or nose-down tendencies and control feel. A rudder jam would show up as unusual yaw or steering difficulty. A stabilizer trim runaway would cause rapid, persistent trimming changes and a strong tendency to alter the flight attitude or trim state, often with autopilot or control surface activity—not just a fluctuating airspeed readout.

So, fluctuating IAS with no configuration change points you to an air data problem and the need to treat the airspeed indication as unreliable, cross-check with other instruments, and follow procedure to maintain safe flight using known parameters and available standby indications.