ACS Electrical Systems & Avionics 3 — Questions and Answers
Question 1: What is the primary function of a static inverter in an aircraft?
- To convert DC power to AC power for avionics and instruments (Correct answer)
- To convert AC power to DC power for battery charging
- To regulate generator output voltage
- To provide emergency DC power from the AC bus
Correct answer: To convert DC power to AC power for avionics and instruments
A static inverter converts aircraft DC power (from the battery or generator) into AC power required by certain avionics and instruments.
Question 2: When performing a bonding check on an aircraft, what maximum resistance is typically acceptable between two airframe components?
- 1.0 ohm
- 0.1 ohm
- 10 ohms
- 0.003 ohm (Correct answer)
Correct answer: 0.003 ohm
FAA AC 43.13-1B specifies that bonding connections should have resistance not exceeding 0.003 ohm (3 milliohms) for effective static discharge and EMI protection.
Question 3: An ADF receiver bearing pointer rotates continuously and does not settle on a station. What is the most likely cause?
- The station is beyond the receiver's range
- A defective or open sense antenna
- Incorrect frequency selection
- A faulty ADF loop antenna (Correct answer)
Correct answer: A faulty ADF loop antenna
A defective loop antenna causes the bearing pointer to continuously rotate since the system cannot determine directional signal phase difference.
Question 4: What does a transponder's MODE C capability provide to ATC?
- Aircraft identification code only
- Aircraft position in latitude and longitude
- Pressure altitude information encoded with the transponder reply (Correct answer)
- Ground speed and heading data
Correct answer: Pressure altitude information encoded with the transponder reply
Mode C transponders encode pressure altitude data (from the aircraft's encoding altimeter) with each reply, allowing ATC to display altitude alongside the target.
Question 5: What is the purpose of a current limiter (fuse link) installed in series with an aircraft alternator?
- To regulate alternator output voltage
- To protect the alternator from reverse current flow
- To protect the main bus wire from excessive current if the alternator fails internally (Correct answer)
- To disconnect the alternator during engine start
Correct answer: To protect the main bus wire from excessive current if the alternator fails internally
A current limiter protects the heavy alternator output cable from damage in the event of an alternator internal short circuit.
Question 6: Which wire gauge would be correct for a 20-ampere circuit run 15 feet in a non-bundle, non-conduit installation?
- 22 AWG
- 20 AWG
- 14 AWG (Correct answer)
- 18 AWG
Correct answer: 14 AWG
Per FAA AC 43.13-1B wire sizing charts, a 20-ampere circuit at 15 feet requires 14 AWG wire to limit voltage drop to 1 volt.
Question 7: A DME indicator shows distance but the reading fluctuates erratically. Which component is most likely at fault?
- The DME antenna (Correct answer)
- The VOR receiver co-located with the DME
- The aircraft power supply voltage regulator
- The DME transponder reply decoder
Correct answer: The DME antenna
An intermittent DME antenna connection causes fluctuating interrogation signal strength, resulting in erratic distance readings.
ACS Electrical Systems & Avionics 3
What is the primary function of a static inverter in an aircraft?