8.6 Engine Inspection, Records, Compression, Borescope, and Airworthiness
Key Takeaways
- Engine inspection combines physical condition, records, life-limited parts, approved data, special inspections, and regulatory requirements.
- Compression and borescope results are diagnostic evidence that must be interpreted with procedures, operating history, and follow-up inspection.
- Airworthiness decisions depend on approved or acceptable data, required records, AD compliance, life limits, and manufacturer instructions.
Inspection Evidence, Records, and Return-to-Service Judgment
Engine inspection is where theory becomes an airworthiness decision. The ACS includes inspection requirements under 14 CFR part 43 and part 91, life-limited parts, special inspections, approved data, service information, airworthiness directives, type certificate data sheets, maintenance records, component checking and servicing, and engine mounts and hardware. A mechanic must inspect both the metal and the paperwork. A clean engine with missing required records may still fail the airworthiness decision.
A powerplant records inspection should confirm engine identity, total time or cycles where required, time since overhaul if tracked, life-limited part status, airworthiness directive compliance, required inspection status, major repairs or alterations, service bulletins or instructions when made mandatory or adopted by the maintenance program, and proper maintenance entries. The written test may ask which records prove compliance. The best answer usually ties the requirement to a specific record, approved data, or regulatory basis.
| Inspection evidence | What it can show | Boundary for decision |
|---|---|---|
| Compression check | Cylinder sealing condition and leakage path clues | Follow engine procedure, temperature condition, and minimum criteria |
| Borescope view | Valve, piston, cylinder wall, and combustion-chamber condition | Interpret with limits and do not overrule required disassembly criteria |
| Oil filter or screen | Metal, carbon, gasket material, contamination | Follow metal evaluation and follow-up inspection guidance |
| Engine mounts and hardware | Load path, security, corrosion, cracks, wear | Compare hardware, torque, and mount condition with approved data |
| Records | ADs, life limits, inspections, maintenance release history | Missing or conflicting records must be resolved before release |
| Special inspection | Overspeed, overtemp, prop strike, fire, sudden stoppage | Use event-specific approved instructions |
Compression testing is both useful and hazardous. The propeller may move, compressed air can rotate the engine, and the test may require warm-engine conditions. Follow the procedure for cylinder position, air pressure, adapter installation, and propeller control. Leakage heard at the exhaust, intake, crankcase breather, or adjacent areas helps localize valve, ring, or gasket issues. Do not use one number alone without considering the manufacturer's method and follow-up criteria.
Borescope inspection adds visual evidence. It can reveal burned valves, tuliping, cracks, detonation signs, scoring, corrosion, deposits, or foreign object damage. However, a borescope image is not a license to ignore limits. If approved data requires removal after a certain finding, the image supports that decision. If the image is unclear, the safe answer is additional inspection, not optimistic release.
Special inspections are event-driven. A propeller strike, sudden stoppage, overspeed, overtemperature, fire, lightning strike, hard landing affecting mounts, or ingestion event can require inspections beyond routine checks. The mechanic must locate the applicable instructions before deciding the engine is serviceable. Service letters, service bulletins, instructions for continued airworthiness, airworthiness directives, and type certificate data sheets may all matter, depending on the requirement and aircraft maintenance program.
Engine mounts and mounting hardware are part of the inspection boundary because they carry loads into the airframe. Cracked mounts, deteriorated isolators, elongated holes, corrosion, missing safetying, incorrect hardware, or loose fasteners can make an otherwise healthy engine unsafe. Inspect lines, hoses, clamps, fire seals, drains, controls, and wiring while access is open. A complete inspection joins condition, records, and procedure into one return-to-service judgment.
What does a differential compression test help evaluate?
Why is a powerplant records inspection part of the airworthiness decision?
A propeller strike occurred on a reciprocating-engine aircraft. What is the correct inspection frame?