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Cylinder head temperature above the blue arc

Aviation Mechanic Powerplant (AMP) practice question 4 of 12 on Engine Instrument Systems. ACS element AM.III.D.K2 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONA large reciprocating engine is being operated in auto-lean. Its cylinder head temperature gauge carries a blue arc that ends at 230 °C, a green arc above that, and a red line at 260 °C. The gauge indicates 232 °C. What does this reading call for?

  1. AContinued operation in the auto-lean setting
  2. BAn immediate shutdown of the engine
  3. CMoving the mixture control to auto-rich
Show the answer and explanation

Correct answer: C. Moving the mixture control to auto-rich

  • A — incorrect The blue arc marks the range in which auto-lean operation is permitted, and the indication has passed the top of that arc.
  • B — incorrect The red line at 260 °C is the maximum permissible cylinder head temperature, and the indicated temperature is well below it.
  • C — correct The top of the blue arc, 230 °C, is defined as the temperature at which the mixture control must be moved to the auto-rich position, and 232 °C is above that point.

BACKGROUND

Cylinder head temperature (CHT) is sensed by a thermocouple attached to the cylinder that testing shows to be the hottest in that installation, usually under a rear spark plug or in a well in the head. The gauge described in the powerplant handbook is a dual gauge with scales graduated every 10 °C. Its blue arc runs from 100 °C, the minimum desired temperature for efficient operation, to 230 °C, the point at which the mixture control must be moved to auto-rich. The green arc is the range in which operation must be in auto-rich, and its top at 248 °C is maximum continuous power, above which operation is time limited. The red line at 260 °C is the maximum permissible cylinder head temperature.

STUDY TIP

Learn the four CHT numbers as a ladder: 100 °C minimum desired, 230 °C go to auto-rich, 248 °C maximum continuous, 260 °C maximum permissible.

KEY POINTS

  • The top of the blue arc at 230 °C is the point to select auto-rich.
  • 248 °C is maximum continuous power; above it, operation is time limited.
  • The red line at 260 °C is the maximum permissible cylinder head temperature.

SOURCES

  • FAA-H-8083-32B ch10 "Cylinder Head Temperature Indicator"
Practice the Aviation Mechanic Powerplant (AMP) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON ENGINE INSTRUMENT SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.