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Altimeter lag after long level flight

Aviation Mechanic Airframe (AMA) practice question 16 of 20 on Aircraft Instrument Systems. ACS element AM.II.H.K19 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONAfter a long period of level flight, an analog altimeter responds sluggishly to an abrupt altitude change. What is this characteristic called?

  1. AScale error.
  2. BHysteresis.
  3. CPosition error.
Show the answer and explanation

Correct answer: B. Hysteresis.

  • A — incorrect Scale error is a mechanical misalignment of the instrument scale and is corrected by periodic testing and adjustment, not by a change of flight profile.
  • B — correct Hysteresis is the term for the diaphragm material taking a set during long periods of level flight, causing the indication to lag during a following rapid altitude change.
  • C — incorrect Position error is the inaccuracy caused by the location of the static vent and varies with speed and attitude, not with time spent in level flight.

BACKGROUND

The pressure altimeter measures absolute pressure with an aneroid, and several distinct inaccuracies affect it. Scale error is a mechanical error in which the scale is not aligned so the pointers indicate correctly, and it is kept small by periodic testing and adjustment with calibrated equipment. Position error, also called installation error, comes from the location of the static vent, because airflow over the airframe changes with speed and attitude; an air data computer can remove it on modern aircraft. Static system leaks can also corrupt the pressure sample, which is why leak checks are required every 24 months regardless of whether a discrepancy has been noticed. Hysteresis is different again: the diaphragm material takes a set during long periods of level flight, so after an abrupt altitude change the indication lags or responds slowly while the diaphragm expands or contracts.

STUDY TIP

Group the altimeter errors by cause: mechanical scale, static vent location, system leaks, temperature, and diaphragm set.

KEY POINTS

  • Hysteresis is diaphragm set after long level flight that makes the indication lag.
  • Scale error is a mechanical misalignment corrected by calibrated testing.
  • Position error comes from the static vent location and can be removed by an air data computer.

SOURCES

  • sources/ama-airframe/ch10.txt "Altimeters & Altitude" (scale error, position error, hysteresis)
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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.