The indicated airspeed jumps erratically with no change in flight attitude.

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

Answer: (D)

Indicated airspeed depends on the pitot-static system to measure dynamic pressure and convert it to a speed reading. If the IAS jumps around while the aircraft’s attitude remains steady, the most likely issue is an unreliable airspeed indication caused by a pitot-static problem—such as a blocked pitot tube, a leaking line, or blocked/static ports. These conditions cause erratic pressure signals to reach the airspeed indicator, so the gauge can swing even though the airplane isn’t changing speed or attitude.

The other options involve changes to the aircraft’s attitude or control surfaces. A jammed elevator or rudder would typically produce cues in pitch or yaw and may require control exceptions, while a stabilizer trim runaway would usually manifest as a pitch change and corresponding speed variation. Since the readings change without any attitude change, the problem aligns with the airspeed indicator itself rather than a mechanical control jam or trim issue.