AM Troubleshooting & Diagnostics 3 — Questions and Answers
Question 1: A turbine engine's exhaust gas temperature (EGT) is higher than normal at takeoff power. Which fault is least likely to be the cause?
- Compressor fouling or damage
- Turbine blade erosion
- Fuel nozzle clogging causing uneven combustion
- Engine oil level low by one quart (Correct answer)
Correct answer: Engine oil level low by one quart
Oil level has little effect on EGT; high EGT is typically caused by reduced compressor efficiency, turbine degradation, or abnormal combustion.
Question 2: When a continuity check on a wire harness shows zero ohms between two conductors that should be separate, this indicates:
- An open circuit
- A short circuit between the two conductors (Correct answer)
- Correct wiring
- High resistance corrosion
Correct answer: A short circuit between the two conductors
Zero ohms between conductors that should be isolated means they are shorted together, creating an unintended electrical path.
Question 3: During ground testing, fuel is found in the engine oil. What is the MOST likely cause on a reciprocating engine?
- Overfilled fuel tanks
- Failed primer system or leaking fuel injection nozzle flooding the intake (Correct answer)
- Fuel pump pressure too high
- Carburetor float level too low
Correct answer: Failed primer system or leaking fuel injection nozzle flooding the intake
Fuel can enter the crankcase via a leaking primer or flooded injection nozzle, allowing raw fuel to pass the rings into the oil.
Question 4: An autopilot system causes repeated uncommanded roll inputs. After verifying the control surfaces are free, the technician should next check:
- The magnetic compass deviation card
- Rate gyro or attitude sensor outputs and autopilot servo feedback signals (Correct answer)
- The fuel quantity imbalance between tanks
- The battery voltage level
Correct answer: Rate gyro or attitude sensor outputs and autopilot servo feedback signals
Uncommanded autopilot roll inputs suggest erroneous sensor data from the rate gyro or attitude sensor, or servo feedback issues.
Question 5: A composite airframe shows a dull thud when tapped in an area that normally produces a sharp tap sound. This indicates:
- Normal variation in composite density
- Delamination or disbonding within the composite layers (Correct answer)
- Surface paint delamination only
- An internal stiffener location
Correct answer: Delamination or disbonding within the composite layers
A dull tap (coin-tap test) on composite structure indicates internal delamination or disbonding between layers.
Question 6: Troubleshooting a brake system that requires excessive pedal travel before braking occurs, the technician should first check:
- Brake pad material thickness
- Hydraulic fluid level and the system for air entrainment (Correct answer)
- Brake disc flatness (runout)
- Anti-skid valve operation
Correct answer: Hydraulic fluid level and the system for air entrainment
Excessive pedal travel in a hydraulic brake system is a classic symptom of low fluid or air in the system, both of which must be corrected before adjusting components.
Question 7: An aircraft oxygen system pressure reads lower than expected after a known-good fill. Which is the BEST next diagnostic step?
- Immediately replace the oxygen cylinder
- Perform a leak check using an approved oxygen-compatible leak detection method (Correct answer)
- Bleed and refill the system
- Check regulator output pressure only
Correct answer: Perform a leak check using an approved oxygen-compatible leak detection method
Unexplained pressure loss requires a leak check using approved soap solutions or electronic detectors rated for oxygen service before any components are replaced.
AM Troubleshooting & Diagnostics 3
A turbine engine's exhaust gas temperature (EGT) is higher than normal at takeoff power.
Which fault is least likely to be the cause?