Turbine Engine Maintenance Flashcards

A technician performing a borescope inspection on a high-bypass turbofan engine discovers several small, smooth-surfaced dents on the leading edges of multiple first-stage compressor blades. What is the most likely cause of this specific type of damage?

Answer: Soft body Foreign Object Damage (FOD)

Smooth-surfaced dents on compressor blades are characteristic of soft body ingestion, such as a bird strike. Hard body FOD (like rocks or metal) typically causes sharp nicks, gouges, and tears. Compressor stalls and fatigue result in different types of damage, usually cracks or fractures.

Which of the following describes the primary long-term effect of operating a turbine engine at or near its maximum temperature limits, which leads to the permanent elongation of turbine blades?

Answer: Creep

Creep is the slow, permanent deformation or stretching of a material caused by prolonged exposure to high levels of stress at high temperatures. Turbine blades are under immense centrifugal stress in a very hot environment, making them susceptible to creep over their service life. Galling, spalling, and brinelling are forms of mechanical surface damage.

What is the primary purpose of performing a routine compressor wash on a turbine engine?

Answer: To remove contaminants from airfoils to restore engine performance

A compressor wash is performed to remove accumulated dirt, salt, and other contaminants from the compressor blades and vanes. This buildup disrupts airflow, reduces compressor efficiency, and causes a rise in Exhaust Gas Temperature (EGT) for a given power setting. Washing cleans the airfoils, restoring aerodynamic efficiency and engine performance.

During a hot section inspection, an A&P technician identifies thermal cracking on several first-stage turbine nozzle guide vanes. What is the most common cause for this type of failure?

Answer: Frequent and rapid thermal cycling

Thermal cracking, or thermal fatigue, is caused by the stress of repeated and rapid heating and cooling cycles. The nozzle guide vanes are directly exposed to the hottest gases from the combustor, and the temperature changes drastically between engine start-up, operation, and shutdown, leading to stress cracks over time.

After replacing a fuel control unit on a turbofan engine, the maintenance manual calls for an engine trim check. What is the primary objective of this procedure?

Answer: To adjust the fuel control to ensure the engine produces rated thrust at specified limits

Trimming a turbine engine involves making fine adjustments to the fuel control system. The goal is to ensure the engine's performance parameters (like Engine Pressure Ratio (EPR), fan speed (N1), or Exhaust Gas Temperature (EGT)) are within the manufacturer's specified limits for a given power lever setting, thus ensuring it can produce its rated thrust without exceeding operational limits.

A technician is approved to perform a minor repair on a small nick in a compressor blade by blending. Which of the following is a critical requirement for a successful blending repair?

Answer: The repair must have smooth, generous radii to prevent stress concentrations.

The most critical principle of blending is to create a smooth, contoured depression with generous radii. This eliminates the sharp edges of the original damage, which act as stress risers where a fatigue crack could form. A sharp-edged or V-shaped repair would create new stress concentrations and is unacceptable.