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Cowl flap position during ground operation

Aviation Mechanic Powerplant (AMP) practice question 1 of 13 on Reciprocating Engine Induction and Cooling Systems. ACS element AM.III.J.R1 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONHow should the cowl flaps be set during ground operation of the engine?

  1. AClosed, to bring the engine up to temperature
  2. BOpened wide, because drag does not matter
  3. CSet to the takeoff position for best airflow
Show the answer and explanation

Correct answer: B. Opened wide, because drag does not matter

  • A — incorrect Closing the flaps decreases the exit area and reduces the airflow over the cylinder fins, which raises engine temperature at the time cooling is needed most.
  • B — correct During ground operations the cowl flaps should be opened wide, since drag does not matter and cooling needs to be set at maximum.
  • C — incorrect On takeoff the flaps are opened only enough to keep the engine below the red-line temperature so that drag stays low; that is less than the ground setting.

BACKGROUND

The most common means of controlling engine cooling is the use of cowl flaps, opened and closed by electric motor-driven jackscrews, by hydraulic actuators, or manually on some light aircraft. When extended for increased cooling, the cowl flaps produce drag and sacrifice streamlining for the added cooling. On takeoff, the cowl flaps are opened only enough to keep the engine below the red-line temperature, allowing heating above the normal range so that drag is as low as possible. During ground operations, the cowl flaps should be opened wide, since drag does not matter and cooling needs to be set at maximum. Closing the cowl flaps decreases the exit area at the rear of the cowling, which decreases the volume of air circulating over the cylinder fins and lets engine temperature increase.

STUDY TIP

Judge cowl flap position by the trade between drag and cooling. On the ground there is no drag penalty, so use maximum cooling.

KEY POINTS

  • Cowl flaps are opened wide during ground operation because drag does not matter.
  • On takeoff they are opened only enough to stay below the red-line temperature.
  • Closing the flaps reduces exit area and airflow, raising engine temperature.

SOURCES

  • amp-powerplant/ch06.txt "Reciprocating Engine Cooling Systems"
  • amp-powerplant/ch06.txt "Reciprocating Engine Cooling System Maintenance"
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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.