During a climb through 6,000 feet, an aircraft's static port suddenly becomes obstructed by ice and the alternate static source is not selected. As the aircraft continues to climb above 6,000 feet, the airspeed indicator will
- Aread accurately because pitot pressure is unaffected
- Bremain frozen at the airspeed shown at 6,000 feet
- Cread lower than the actual airspeed
- Dread higher than the actual airspeed
Show answer & explanationAnswer & explanation
Correct answer: C. read lower than the actual airspeed
With the static line blocked, the static reference pressure stays fixed at the value present at the blockage altitude (a higher pressure than the true, lower ambient pressure encountered while climbing). Because airspeed is derived from pitot pressure minus static pressure, using a static pressure that is too high results in a differential that is smaller than actual, so the indicator underreads as the aircraft climbs above the blockage point.
Why the other options are wrong
- A. Airspeed indication depends on both pitot and static pressure, so a static blockage does affect it.
- B. Only the altimeter and VSI freeze; the airspeed indicator still changes because pitot pressure continues to vary.
- D. This would occur during a descent below the blockage altitude, not a climb above it.
Blocked Static Port
When the static port is obstructed, the airspeed indicator behaves like an altimeter, under-reading during a climb above the blockage point and over-reading during a descent below it.
- Static pressure freezes at the value present at the moment of blockage
- Airspeed = pitot pressure minus static pressure
- Altimeter and VSI freeze completely when static-blocked
- Alternate static source should be selected to restore accurate readings
Memory trick: 'Static stuck, speed's outta luck' — climb high, speed reads low.