Turbine Engine Inspection, Troubleshooting, and Compressor Wash

Objective. Students will perform a borescope inspection of turbine engine hot-section and compressor components, evaluate findings against serviceable limits, conduct a compressor wash, and document results in a maintenance record.

Turbine Engine Inspection, Troubleshooting, and Compressor Wash

Maintaining a turbine engine in an airworthy condition depends on systematic inspection, accurate damage evaluation, and meticulous recordkeeping. This lab covers three interconnected tasks every A&P mechanic performs on turbine powerplants: borescope inspection of hot-section and compressor components, compressor wash, and fault isolation using a fault isolation manual (FIM).

Borescope Inspection

A video borescope is a flexible or rigid optical instrument with a small camera head that lets you examine internal engine passages without disassembly. Modern units record still images and video, giving you a permanent inspection record.

Preparation and Safety. Before inserting the scope, confirm the engine is de-energized and tagged out under your shop's lockout/tagout (LOTO) procedure. Rotating components must be stationary and locked. Wear eye protection at all times. If a training engine is on a stand, verify that fuel and ignition systems are isolated.

Access Ports. Compressor stages are reached through borescope ports drilled between stages; turbine sections are accessed through combustion liner ports or dedicated hot-section plugs. Always consult the manufacturer maintenance manual (MM) for the exact port locations and scope diameter limits before insertion.

What to Look For. Record every finding by stage, blade number, and clock position (viewed from the front, 12 o'clock is top dead center). Common findings include:

Nicks and dents — small material displacements from FOD strikes
Tip rubs — abrasion at blade tip caused by contact with the case
Cracks — linear separations; most are cause for rejection
Erosion — gradual material loss from particle ingestion
FOD damage — any deformation from foreign-object debris

Evaluating Against Allowable Limits. The manufacturer's allowable damage limits table specifies maximum nick depth, width, length, and spacing for each stage. A finding is serviceable when all dimensions fall within limits; it is unserviceable (reject) when any dimension exceeds a limit or when a crack of any size is found on a blade airfoil. Document each finding with a sketch or captured image, the measured or estimated dimensions, and your serviceable/unserviceable determination. Your signature on the record is a legal maintenance entry.

Compressor Wash

Salt, dirt, and combustion byproducts accumulate on compressor blades and reduce aerodynamic efficiency — a condition called compressor fouling. A compressor wash restores performance and protects against corrosion.

Types of Wash. A desalination rinse uses clean, demineralized water to remove salt deposits. A detergent wash uses an approved cleaning solution followed by a water rinse to remove oily deposits. Always use the fluid type and dilution ratio specified in the MM; substituting unapproved chemicals can damage coatings or seals.

Wash Procedure (General Sequence).

1. Confirm the engine is at the correct cool-down temperature per the MM — washing a hot engine can cause thermal shock.

2. Don chemical-resistant gloves and eye protection in addition to hearing protection if the engine will be motored.

3. Prepare wash fluid to the specified dilution using demineralized water and measure the concentration if a refractometer or test kit is required.

4. Connect the wash manifold ring or spray nozzle to the engine inlet per MM instructions.

5. Apply fluid at the specified flow rate while motoring the engine (starter only, no ignition) or by gravity feed, depending on the MM procedure.

6. Follow with a clean-water rinse to remove all detergent residue.

7. Perform a dry-motoring run to purge residual fluid from the engine internals before any return to service.

8. Effluent collection. Wash runoff may contain oils, metals, and cleaning agents — it is shop waste and must be collected and disposed of according to your shop's environmental procedures and applicable regulations. Never allow effluent to enter a floor drain connected to a public sewer without authorization.

9. Record the wash in the engine's maintenance log with the date, fluid used, dilution ratio, and your certificate number and signature.

Fault Isolation and Troubleshooting

A fault isolation manual (FIM) organizes troubleshooting into flowcharts or decision trees keyed to specific fault codes or observed symptoms. Working the chart systematically prevents guesswork.

Common Turbine Engine Malfunctions.

High exhaust gas temperature (EGT): May indicate compressor fouling, fuel control malfunction, combustion liner damage, or turbine blade deterioration.
Low oil pressure: Check oil level first; then suspect pressure-relief valve, scavenge pump, or internal leak.
Compressor stall: Characterized by a loud bang and surge in EGT/torque; causes include damaged inlet guide vanes, FOD, rapid throttle movement, or icing.
Hung start: Engine lights off but N1 speed does not accelerate to idle; suspect insufficient starter torque, fuel control issue, or hot-section restriction.

Documentation. Each troubleshooting session must be recorded: symptom observed, FIM reference used, tests performed, findings, and recommended corrective action. This record supports continued airworthiness and is subject to FAA review.

Safety Summary

Apply LOTO before any borescope insertion or wash prep on an installed engine.
Use correct PPE for each task: hearing protection during motoring runs, chemical-resistant gloves and eye protection during wash, eye protection during borescope work.
Never introduce foreign objects into borescope ports beyond the scope probe.
Collect and properly dispose of all wash effluent.
All maintenance entries must be accurate, legible, and signed with your FAA certificate number.

Key terms10

BorescopeA flexible or rigid optical instrument with a camera head used to inspect internal engine components through access ports without disassembly.

Allowable damage limitsManufacturer-specified maximum dimensions (depth, width, length) for nicks, dents, and other surface damage beyond which a component is classified unserviceable.

Compressor foulingAccumulation of salt, dirt, or oily deposits on compressor blade airfoils that reduces aerodynamic efficiency and can accelerate corrosion.

Clock positionA method of locating a finding inside an engine by reference to a clock face viewed from the front of the engine, with 12 o'clock at the top.

Fault isolation manual (FIM)A structured troubleshooting guide that uses decision-tree flowcharts keyed to symptoms or fault codes to direct a mechanic to the probable cause of a malfunction.

Compressor stallAn aerodynamic disruption in which airflow through the compressor separates from blade surfaces, causing a surge accompanied by a bang and spike in exhaust gas temperature.

Hung startA condition in which a turbine engine ignites but N1 rotor speed fails to accelerate to idle, indicating insufficient energy or a restriction preventing normal acceleration.

EffluentLiquid waste produced during a compressor wash, which may contain lubricating oils, metal particles, and cleaning agents and must be collected and disposed of per environmental regulations.

Desalination rinseA compressor wash using demineralized water only, performed to remove salt deposits from compressor blades and prevent corrosion.

FOD (Foreign Object Damage)Damage to engine components caused by ingestion of any foreign object such as stones, hardware, ice, or wildlife.

In class: Using a video borescope, inspect accessible compressor and turbine blades on a training engine for nicks, dents, tip rubs, cracks, and FOD damage; record each finding with its location (stage, blade number, clock position) and evaluate against the manufacturer's allowable damage limits chart. · Perform an on-wing compressor wash following the manufacturer's procedure: dilute wash fluid per specification, apply through the inlet, collect and dispose of effluent per shop environmental procedures, and record the wash in the maintenance log. · Troubleshoot four instructor-simulated turbine engine malfunctions (e.g., high exhaust gas temperature, low oil pressure, compressor stall indication, hung start) using a fault isolation manual flowchart and document the diagnosis and recommended corrective action.
Materials: Training turbine engine (on stand or mounted); video borescope with recording capability; compressor wash kit and approved wash fluid; manufacturer maintenance manual and allowable damage limits tables; fault isolation manual; maintenance record forms; PPE (hearing protection, eye protection, chemical-resistant gloves)
Check: All borescope findings accurately recorded with location and serviceable/unserviceable determination matching instructor key; compressor wash performed in correct sequence with no environmental violations; at least three of four fault-isolation diagnoses correct; lab log signed off.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.