FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesHard
A technician discovers that a reciprocating engine's crankcase breather line is completely blocked with ice during a flight in cold, moist conditions. What is the most likely consequence of this blockage?
- AA drop in oil pressure due to reduced crankcase suction
- BA rise in cylinder head temperature due to restricted cooling airflow
- CAn immediate loss of engine oil pressure indication on the gauge
- DIncreased crankcase internal pressure, potentially forcing oil out through seals and gaskets
Show answer & explanationAnswer & explanation
Correct answer: D. Increased crankcase internal pressure, potentially forcing oil out through seals and gaskets
The crankcase breather vents blow-by gases and pressure buildup (from piston ring blow-by) to the atmosphere. If the vent line freezes shut, crankcase pressure builds up with nowhere to escape, and this excess pressure can force oil out past seals, gaskets, and the dipstick/filler cap, leading to oil loss and potential leaks rather than a pressure gauge indication change.
Why the other options are wrong
- A. Blockage increases pressure rather than creating suction; oil pressure at the pump is largely unaffected initially.
- B. The breather line has no function related to cylinder cooling airflow.
- C. Oil pressure gauge indication reflects pump discharge pressure, not crankcase internal pressure, and is not directly affected.
Crankcase Breather (Vent) System
A vent line that relieves crankcase pressure caused by piston ring blow-by gases, routing them overboard; blockage causes pressure buildup and potential oil leaks.
- Vents combustion blow-by gases from crankcase
- Blockage (often by ice) raises internal crankcase pressure
- Excess pressure can force oil out at seals, gaskets, or dipstick
Memory trick: 'Blocked breather, oil goes everywhere'