4L Emergencies - Pitot/Static and Associated Instruments

Question 0

1. What instruments are affected when the pitot tube freezes? (FAA-H-8083-25)

Answer 0

a. Pitot tube blocked and associated drain hole remains clear—Airspeed decreases to zero, altimeter and vertical speed read normal.
b. Pitot tube and drain hole blocked—Airspeed indicator acts as an altimeter; reads high in climb and low in descent. Altimeter and vertical speed read normal.

Question 1

2. What instruments are affected when the static port freezes? (FAA-H-8083-25)

Answer 1

Airspeed Indicator—Accurate at the altitude frozen as long as the static pressure in the indicator and the system equals outside pressure. If the aircraft descends, the airspeed indicator would read high (outside static pressure greater than that trapped). If the aircraft climbs, the airspeed indicator will read low.
Altimeter—Indicates the altitude at which the system was blocked.
Vertical speed—Indicates level flight.

Question 2

3. Does the pitot system have any protection from ice?

Answer 2

Yes. The heated pitot system consists of the following components:

a. A pitot tube with a heating element,
b. A “pitot heat” rocker switch, and
c. A 10-amp push-to-reset circuit breaker.

Question 3

4. What corrective action is needed if the pitot tube freezes? If the static port freezes? (FAA-H-8083-25)

Answer 3

Pitot tube—Turn pitot heat on.

Static port—Use alternate air if available, or break the face of a static instrument (either the VSI or A/S indicator).

Question 4

5. What indications should you expect while using alternate air? (FAA-H-8083-15)

Answer 4

In many unpressurized aircraft equipped with a pitot-static tube, an alternate source of static pressure is provided for emergency use. If the alternate source is vented inside the airplane, where static pressure is usually lower than outside, selection of the alternate static source may result in the following indications:
Altimeter—will indicate higher than the actual altitude
Airspeed—will indicate greater than the actual airspeed
Vertical speed—will indicate a climb while in level flight
Note: Always consult the AFM/POH to determine the amount of error.