AET Technical Knowledge and Skills 2 — Questions and Answers
Question 1: What is the standard word length for data transmitted on an ARINC 429 data bus?
- 16 bits
- 24 bits
- 32 bits (Correct answer)
- 64 bits
Correct answer: 32 bits
ARINC 429 uses a 32-bit word format that includes label, source/destination identifier, data, sign/status matrix, and parity bit fields.
Question 2: A VOR receiver indicates a 'TO' flag with full left CDI deflection. The aircraft is flying directly TOWARD the station. What is the most likely cause?
- The OBS is set 90° off from the inbound course (Correct answer)
- The aircraft is on the correct course and the CDI is calibrated correctly
- The VOR station is transmitting an alarm signal
- The receiver AGC circuit has failed
Correct answer: The OBS is set 90° off from the inbound course
A full CDI deflection with a TO flag while flying toward the station indicates the OBS course selector is set approximately 90° off from the actual bearing to the station.
Question 3: Standard aircraft AC bus voltage and frequency for most commercial transport aircraft is:
- 28V AC at 400 Hz
- 115V AC at 60 Hz
- 115V AC at 400 Hz (Correct answer)
- 26V AC at 400 Hz
Correct answer: 115V AC at 400 Hz
Most transport-category aircraft use 115V AC at 400 Hz, which allows smaller and lighter transformer and motor designs compared to 60 Hz ground power.
Question 4: Which component of an ILS system provides lateral course guidance to the runway centerline?
- Glide slope transmitter
- Outer marker beacon
- Localizer transmitter (Correct answer)
- Middle marker beacon
Correct answer: Localizer transmitter
The localizer transmitter, located beyond the departure end of the runway, radiates two overlapping lobes on 90 Hz and 150 Hz to provide lateral guidance to the runway centerline.
Question 5: A Mode C transponder reply includes which of the following information?
- Aircraft ID and heading
- Aircraft ID only
- Pressure altitude and squawk code (Correct answer)
- GPS position and altitude
Correct answer: Pressure altitude and squawk code
Mode C transponder replies encode the aircraft's pressure altitude (in 100-ft increments) along with the 4-digit squawk code assigned by ATC.
Question 6: DME (Distance Measuring Equipment) operates on the principle of measuring:
- The phase difference between two RF signals
- Round-trip pulse propagation time between aircraft and ground station (Correct answer)
- Doppler shift of a carrier frequency
- Signal strength attenuation over distance
Correct answer: Round-trip pulse propagation time between aircraft and ground station
DME measures the slant-range distance by timing the round-trip delay between an interrogation pulse sent by the aircraft and the reply pulse from the ground transponder.
Question 7: When troubleshooting an avionics system using a dual-trace oscilloscope, what is the primary advantage of using the 'chop' mode versus 'alternate' mode at low frequencies?
- Chop mode provides higher bandwidth for fast signals
- Chop mode switches between traces rapidly enough that both appear continuous at low sweep speeds (Correct answer)
- Chop mode eliminates ground loops in the measurement
- Chop mode automatically triggers on both channels simultaneously
Correct answer: Chop mode switches between traces rapidly enough that both appear continuous at low sweep speeds
At low sweep speeds, chop mode rapidly switches between channels many times per sweep so both traces appear solid, whereas alternate mode only updates one trace per sweep causing flicker.
AET Technical Knowledge and Skills 2
What is the standard word length for data transmitted on an ARINC 429 data bus?