AET AET Aircraft Power Systems 5 — Questions and Answers
Question 1: What condition causes a thermal runaway in an aircraft nickel-cadmium battery?
- Excessively low ambient temperature during charging
- A self-sustaining cycle where heat increases charge acceptance, further increasing heat (Correct answer)
- Repeated shallow discharge cycles below 50% capacity
- Overloading the battery with high-resistance loads
Correct answer: A self-sustaining cycle where heat increases charge acceptance, further increasing heat
Thermal runaway occurs when rising battery temperature increases its ability to accept charge current, generating more heat in a self-reinforcing cycle that can lead to fire.
Question 2: Which component in an aircraft AC power system is responsible for detecting a generator fault and removing it from the bus?
- Current Transformer (CT)
- Generator Control Unit (GCU) (Correct answer)
- Transformer Rectifier Unit (TRU)
- Constant Speed Drive (CSD)
Correct answer: Generator Control Unit (GCU)
The Generator Control Unit monitors generator output parameters and trips the Generator Control Breaker (GCB) to disconnect a faulty generator from the bus.
Question 3: An aircraft Transformer Rectifier Unit (TRU) converts:
- DC battery power to AC for avionics
- 28V DC to 115V AC for large loads
- 115V AC three-phase to 28V DC (Correct answer)
- 400 Hz AC to 60 Hz AC for ground equipment
Correct answer: 115V AC three-phase to 28V DC
A TRU uses a transformer to step down voltage and a rectifier bridge to convert three-phase 115V AC aircraft power into 28V DC for DC-powered systems.
Question 4: What is the purpose of a Constant Speed Drive (CSD) on a conventional aircraft AC generator?
- Maintain constant generator output voltage regardless of load
- Drive the generator at a constant rotational speed regardless of engine RPM (Correct answer)
- Prevent overspeeding of the hydraulic pump
- Regulate the generator field excitation current
Correct answer: Drive the generator at a constant rotational speed regardless of engine RPM
The CSD is a hydromechanical device that converts varying engine shaft speed into a constant output speed, ensuring the generator produces 400 Hz AC power.
Question 5: During an aircraft battery capacity check, what indicates a serviceable NiCd battery?
- Battery maintains charge indefinitely with no load applied
- Battery delivers rated ampere-hour capacity to a specified end-cell voltage (Correct answer)
- Individual cells measure exactly 1.2V under full charge with no variation
- Battery temperature stays below ambient during a 1-hour discharge
Correct answer: Battery delivers rated ampere-hour capacity to a specified end-cell voltage
A NiCd battery passes a capacity check when it can deliver its rated ampere-hour capacity while maintaining voltage above the minimum end-cell cutoff voltage.
Question 6: In aircraft wiring, what is the primary reason for twisting wire pairs used for sensitive avionics circuits?
- Reduce wire weight by eliminating shielding
- Cancel electromagnetic interference through opposing field cancellation (Correct answer)
- Improve insulation resistance at high altitudes
- Increase current-carrying capacity of the conductors
Correct answer: Cancel electromagnetic interference through opposing field cancellation
Twisting wire pairs causes their magnetic fields to cancel each other, greatly reducing susceptibility to electromagnetic interference (EMI) pickup.
Question 7: What does a 'split bus' configuration provide in an aircraft electrical power system?
- Higher voltage output for engine start
- Electrical isolation between buses so a single fault cannot affect all systems simultaneously (Correct answer)
- Faster load shedding during generator failure
- Direct connection of all generators to a single master bus
Correct answer: Electrical isolation between buses so a single fault cannot affect all systems simultaneously
A split bus configuration isolates major electrical buses from each other so that a failure or fault on one bus does not propagate to and disable other buses.
AET AET Aircraft Power Systems 5
What condition causes a thermal runaway in an aircraft nickel-cadmium battery?