A&P Turbine Engine Systems Inspection Questions and Answers — Questions and Answers
Question 1: A technician performing a borescope inspection on a turbine engine's hot section observes small, pitted, and corroded-looking areas on the turbine blades, a condition not consistent with impact damage. This type of high-temperature corrosion, often found in engines operating in salt-laden or industrial environments, is known as what?
- Foreign Object Damage (FOD)
- Sulfidation (Correct answer)
- Creep
- Thermal Fatigue
Correct answer: Sulfidation
Sulfidation is a form of high-temperature corrosion that attacks turbine blades and vanes. It's caused by a chemical reaction between sulfur compounds in the fuel and salt ingested from the air, creating a corrosive mixture at high temperatures. This damage appears as pitting and corrosion, unlike the dents and nicks from FOD, the slow stretching from creep, or the cracking from thermal fatigue.
Question 2: During a routine inspection of a turbine engine's compressor section, a small nick is found on the leading edge of a blade. What is the generally accepted repair method for this type of minor damage, provided it is within the limits specified by the engine maintenance manual?
- Welding the damaged area with a compatible alloy.
- Stop-drilling both ends of the nick to prevent cracking.
- Blending the damaged area smooth with a fine file or stone. (Correct answer)
- Replacing the entire compressor stage.
Correct answer: Blending the damaged area smooth with a fine file or stone.
The standard and approved procedure for repairing minor nicks and scratches on compressor blades is blending. This process involves carefully removing material with a file or stone to create a smooth, contoured surface, which eliminates the stress concentration caused by the sharp edges of the nick and prevents crack formation. Welding is not a field-level repair, stop-drilling is for cracks, and replacing an entire stage for minor damage is unnecessary and not cost-effective.
Question 3: Which of the following non-destructive inspection (NDI) methods is most effective for detecting minute surface and near-subsurface cracks in a conductive turbine engine component, such as a turbine disk, often without requiring its complete removal from the engine?
- Borescope Inspection
- Tap Testing
- Magnetic Particle Inspection
- Eddy Current Inspection (Correct answer)
Correct answer: Eddy Current Inspection
Eddy current inspection uses electromagnetic induction to detect surface and near-subsurface flaws in conductive materials. It is highly sensitive to small cracks and is a preferred method for inspecting critical components like turbine disks and blades in-situ. Borescope is a visual method, tap testing is for composites, and magnetic particle inspection requires the part to be ferrous and is primarily for surface-breaking flaws.
Question 4: A technician inspects a magnetic chip detector from a turbofan engine's oil system and finds a small quantity of fine, fuzzy metallic particles. What is the most appropriate first course of action?
- Consult the engine maintenance manual for specific criteria on particle analysis. (Correct answer)
- Immediately ground the aircraft and schedule the engine for overhaul.
- Drain the oil system and flush it with an approved solvent.
- Clean the chip detector, reinstall it, and perform an engine ground run.
Correct answer: Consult the engine maintenance manual for specific criteria on particle analysis.
The engine maintenance manual contains specific instructions and limits for the type, size, and quantity of particles found on a magnetic chip detector. The first step is always to consult this documentation to determine if the findings are within acceptable limits or if further action, such as oil filter inspection or spectrographic oil analysis, is required. Overhauling the engine or simply cleaning the plug without investigation are inappropriate initial steps.
Question 5: What is the primary operational limit that the Exhaust Gas Temperature (EGT) indicating system is designed to protect?
- Compressor stall margin.
- Maximum fuel flow pressure.
- Turbine inlet temperature limits. (Correct answer)
- Accessory gearbox oil temperature.
Correct answer: Turbine inlet temperature limits.
The EGT indicating system measures the temperature of the exhaust gases as they leave the combustion chamber and enter the turbine section. This reading provides the most practical indication of the Turbine Inlet Temperature (TIT), which is the most critical temperature in the engine. Exceeding the TIT limits can cause severe damage to the turbine blades and vanes, which are the most temperature-sensitive components.
Question 6: During a borescope inspection of a combustor can, a technician observes a significant buildup of hard carbon deposits on a fuel nozzle tip, a condition known as coking. Which of the following is the most likely result of this condition?
- A uniform decrease in engine operating temperature.
- A distorted fuel spray pattern causing localized hot spots. (Correct answer)
- An increase in the engine's overall compression ratio.
- Improved fuel atomization and combustion efficiency.
Correct answer: A distorted fuel spray pattern causing localized hot spots.
Coking on a fuel nozzle disrupts the intended shape and atomization of the fuel spray. This leads to an uneven distribution of fuel within the combustor, which can create localized areas of intense heat known as hot spots. These hot spots can cause severe damage, such as burning or cracking of the combustor liner or turbine vanes. Coking degrades, rather than improves, combustion efficiency.
