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Direction for blowing out pitot-static lines

Aviation Mechanic Airframe (AMA) practice question 4 of 20 on Aircraft Instrument Systems. ACS element AM.II.H.K9 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONDry compressed air is to be blown through the lines of a pitot-static system to clear moisture. In which direction must it be blown?

  1. AFrom the pitot and static ports inward.
  2. BFrom either end, provided drains are open.
  3. CFrom the instrument end toward the ports.
Show the answer and explanation

Correct answer: C. From the instrument end toward the ports.

  • A — incorrect Blowing inward would drive moisture and debris toward the instruments, which is the direction the procedure prohibits.
  • B — incorrect Open drains do not change the required direction of flow; the procedure specifies one direction regardless of drains.
  • C — correct The handbook directs the technician to disconnect all pitot-static instruments and always blow from the instrument end of the system toward the pitot and static ports.

BACKGROUND

Water trapped in a pitot-static system can cause inaccurate or intermittent flight instrument indications, and the problem becomes worse if that water freezes in flight. Many systems have drains at the low points so moisture can be removed during maintenance, and a system with drains can be drained without requiring a leak check afterward. When drains are absent, dry compressed air or nitrogen may be blown through the lines instead. All pitot-static instruments must be disconnected first, and the air is always blown from the instrument end of the system toward the pitot and static ports so that contamination is carried away from the instruments. This blowing procedure must be followed by a leak check, and the technician must confirm that any drains are closed and secured in accordance with approved maintenance procedures.

STUDY TIP

Link the direction rule to its reason: always push contamination away from the instruments, then remember that blowing the lines always triggers a leak check.

KEY POINTS

  • Disconnect all pitot-static instruments before blowing out the lines.
  • Blow from the instrument end toward the pitot and static ports.
  • Blowing the lines must be followed by a leak check; simple draining need not be.

SOURCES

  • sources/ama-airframe/ch10.txt "Pitot-Static System Maintenance & Tests"
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MORE ON AIRCRAFT INSTRUMENT SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.