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Calendar limit on oil system servicing

Aviation Mechanic Powerplant (AMP) practice question 1 of 9 on Engine Lubrication Systems. ACS element AM.III.G.K6 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONAn engine with a full-flow oil filtration system has accumulated 30 hours since its last oil service, which was performed 4 months ago. Under the typical recommendations, what is indicated?

  1. AWait until 25 hours more accumulate
  2. BWait until 50 hours have accumulated
  3. CService the oil system now
Show the answer and explanation

Correct answer: C. Service the oil system now

  • A — incorrect The 25-hour figure applies to engines employing a pressure screen system and to the first service on new or newly overhauled engines, and in any case the calendar limit has already been reached.
  • B — incorrect The 50-hour interval applies to full-flow filtration systems, but the 4-month calendar maximum is reached first and governs here.
  • C — correct A time maximum of 4 months between servicing is recommended in addition to the hourly interval, so reaching 4 months calls for service even though only 30 hours have accumulated.

BACKGROUND

Oil in service is constantly exposed to harmful substances such as gasoline, moisture, acids, dirt, carbon, and metallic particles, so common practice is to drain the entire lubrication system at regular intervals and refill with new oil. A typical interval for oil change is 25 hours, along with a pressure screen cleaning and oil sump suction screen check, for all engines employing a pressure screen system. Typical 50-hour interval oil changes generally include oil filter replacement and a suction screen check for all engines using full-flow filtration systems. One manufacturer also recommends the first oil change and screen cleaning at 25 hours for new, remanufactured, or newly overhauled engines and for engines with newly installed cylinders. A time maximum of 4 months between servicing is also recommended for oil system service.

STUDY TIP

Whenever an interval has both an hourly and a calendar limit, service at whichever comes first. Note which interval goes with a pressure screen system and which goes with a full-flow filtration system.

KEY POINTS

  • Pressure screen systems typically use a 25-hour oil change with screen cleaning.
  • Full-flow filtration systems typically use a 50-hour oil change with filter replacement.
  • A maximum of 4 months between servicing is recommended regardless of hours flown.

SOURCES

  • sources/amp-powerplant/ch06.txt "Oil & Filter Change & Screen Cleaning"
  • sources/amp-powerplant/ch06.txt "Draining Oil"
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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.