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Wet-sump system and inverted flight

Aviation Mechanic Powerplant (AMP) practice question 7 of 9 on Engine Lubrication Systems. ACS element AM.III.G.K3 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONA mechanic is asked why a simple wet-sump lubrication system is not readily adaptable to inverted flying. What is the reason?

  1. AThe scavenge pump cannot prime when inverted.
  2. BOil foams and loses its load-carrying film.
  3. CThe entire oil supply floods the engine.
Show the answer and explanation

Correct answer: C. The entire oil supply floods the engine.

  • A — incorrect A simple wet-sump system has no scavenge pump; oil drains back to the sump by gravity, and scavenge pumps belong to dry-sump systems.
  • B — incorrect Foaming is caused by oil mixing with air and is controlled by tank return-line design and baffles; it is not the stated reason a wet-sump system is unsuited to inverted flight.
  • C — correct In a wet-sump system the oil supply is carried in the sump under the engine, so inverting the aircraft allows the whole supply to flood the engine.

BACKGROUND

A wet-sump system stores the oil supply in a sump or pan that forms part of the engine, and the quantity is limited by the sump capacity. Oil level is measured by a vertical rod that protrudes into the oil from an elevated hole on top of the crankcase, and a screen strainer in the bottom of the sump strains particles before the oil reaches the suction side of the pressure pump. Parts oiled by pressure throw a lubricating spray into the cylinder and piston assemblies, after which the oil drains back into the sump and the cycle repeats. Because the reservoir is simply the bottom of the engine, the system is not readily adaptable to inverted flying, since the entire oil supply floods the engine. The lubrication system must function properly in all flight attitudes the aircraft is expected to operate in, and in wet sump engines that requirement must be met when only half of the maximum lubricant supply is in the engine.

STUDY TIP

Contrast the two basic systems by asking where the oil is stored: inside the engine for wet sump, in a separate tank for dry sump. That single difference explains the flooding limitation and the need for scavenge pumps in dry-sump installations.

KEY POINTS

  • A wet-sump system stores the oil in a sump that is part of the engine.
  • Oil drains back into the sump by gravity after lubricating the moving parts.
  • Inverted flight floods the engine with the entire oil supply, so the system is not readily adaptable to it.

SOURCES

  • sources/amp-powerplant/ch06.txt "Wet-Sump Lubrication System Operation"
  • sources/amp-powerplant/ch06.txt "Lubrication System Requirements"
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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.