Engine Inspection
What is required
Inspection questions test whether you know what is required, what authorizes it, and how to perform the common checks.
Required inspections include the annual inspection (or the 100-hour inspection for aircraft carrying persons for hire), progressive inspections, and inspections mandated by airworthiness directives. Know the difference between an AD (mandatory and regulatory) and a service bulletin (usually recommended unless an AD makes it mandatory).
Core skills: reading the engine logbook for compliance, checking corrosion and preservation status, borescope inspection of cylinders and turbine hot sections, oil analysis, oil filter and pressure screen inspection, magnetic chip detectors, and the differential compression test.
The differential compression test
Apply 80 psi through a calibrated orifice to a cylinder at TDC on the compression stroke. The gauge shows how much pressure the cylinder holds; leakage greater than 25 percent (a reading below 60 psi) requires investigation. Locate the leak by sound: air at the exhaust pipe means the exhaust valve; at the air intake or carburetor means the intake valve; at the crankcase breather or oil filler means rings. A master orifice check confirms the gauge itself is accurate.
Traps
Confusing a 100-hour inspection with an annual; assuming a service bulletin is automatically mandatory; forgetting that air leaking past the rings pressurizes the crankcase and can blow oil out the breather. Compression should be checked with the engine warm and the piston at TDC, and on some engines rocker arms must be loosened so the valves seat.