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Combustion chamber secondary cooling air temperature drop

Aviation Mechanic Powerplant (AMP) practice question 5 of 9 on Turbine Engine Air Systems. ACS element AM.III.K.K1 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONSecondary (cooling) air flowing between the outer casing and a can-type combustion liner lowers the combustion gases from about 3,500 °F to near 1,500 °F. Approximately how much is the gas temperature reduced?

  1. AAbout 1,000 °F, half of the drop
  2. BAbout 5,000 °F, the two added
  3. CAbout 2,000 °F
Show the answer and explanation

Correct answer: C. About 2,000 °F

  • A — incorrect A 1,000 °F reduction would leave the gases near 2,500 °F, far above the stated 1,500 °F value.
  • B — incorrect Adding the two temperatures is not the reduction; the reduction is the difference between them.
  • C — correct The gases leave the burning zone at about 3,500 °F and are cooled to near 1,500 °F, a reduction of roughly 2,000 °F.

BACKGROUND

In a gas turbine engine only part of the air entering a combustion chamber is burned. The liner is perforated with holes, louvers, and slots that split the incoming air into two main streams. Primary (combustion) air enters at the front of the liner and mixes with fuel, while secondary (cooling) air passes between the outer casing and the liner and rejoins the gas stream through larger holes farther aft. That secondary air cools the combustion gases from about 3,500 °F to near 1,500 °F so the turbine section can survive them. Louvers along the length of the liner also lay a film of cooling air along the inside wall, which helps keep the flame centered and prevents the liner walls from burning.

STUDY TIP

Remember the pair of numbers 3,500 °F and 1,500 °F, and practice subtracting them; the test may ask for either the end temperature or the size of the drop.

KEY POINTS

  • Liner holes divide incoming air into primary (combustion) air and secondary (cooling) air.
  • Secondary air cools the gases from about 3,500 °F to near 1,500 °F, a drop of roughly 2,000 °F.
  • Louvers film-cool the inside of the liner wall and help keep the flame centered.

SOURCES

  • amp-powerplant ch01 "Combustion Section" (can-type liner primary and secondary air)
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MORE ON TURBINE ENGINE AIR 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.