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Compressor discharge air temperature and the aftercooler

Aviation Mechanic Powerplant (AMP) practice question 7 of 13 on Reciprocating Engine Induction and Cooling Systems. ACS element AM.III.J.K4 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONMost turbochargers can raise induction air temperature by a factor of five. At full takeoff power on a 100 °F day, what temperature could the air leaving the compressor reach?

  1. AAbout 500 °F
  2. BAbout 230 °F
  3. CAbout 300 °F, the throttle inlet limit
Show the answer and explanation

Correct answer: A. About 500 °F

  • A — correct Five times 100 °F gives about 500 °F, which is why full power takeoff on a 100 °F day can produce induction air exiting the compressor at up to 500 °F.
  • B — incorrect 230 °F is the low end of the typical maximum allowable throttle air inlet temperature, not the temperature the compressor can produce.
  • C — incorrect 300 °F is the high end of the typical maximum throttle air inlet temperature range; the compressor discharge can far exceed it.

BACKGROUND

An aftercooler is installed in the induction air path between the compressor stage and the air throttle inlet. Most turbochargers are capable of compressing induction air to the point at which the air temperature is raised by a factor of five, so full power takeoff on a 100 °F day could produce induction air leaving the compressor at up to 500 °F. Typical maximum air throttle inlet temperatures run from a low of 230 °F to a high of 300 °F, so uncooled compressor discharge air would exceed the limit on every reciprocating engine model. Exceeding those maximums places the combustion chambers closer to detonation. The aftercooler cools the compressed air, which reduces the likelihood of detonation and increases charge air density.

STUDY TIP

Multiply the outside air temperature by five to see why an aftercooler is needed, then compare the result with the 230 °F to 300 °F throttle inlet limits.

KEY POINTS

  • Turbocharger compression can multiply induction air temperature by about five.
  • Maximum air throttle inlet temperatures typically range from 230 °F to 300 °F.
  • The aftercooler cools compressed air to reduce detonation risk and raise charge density.

SOURCES

  • amp-powerplant/ch03.txt "Turbocharger Controllers & System Descriptions"
Practice the Aviation Mechanic Powerplant (AMP) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON RECIPROCATING ENGINE INDUCTION AND COOLING 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.