AET Data Bus Systems and Protocols

Question 1

What is the primary architectural characteristic of the ARINC 429 data bus used in commercial transport avionics?

Accepted Answer

Unidirectional simplex bus with one transmitter and up to 20 receivers

Answer

ARINC 429 is a simplex (one-way) bus: a single transmitter sends data to up to 20 receivers on the same wire pair. If two-way communication is needed, a second separate ARINC 429 bus must be used in the opposite direction.

Question 2

What is the maximum data transfer rate of the MIL-STD-1553B data bus commonly used in military aircraft?

Accepted Answer

1 Mbps

Answer

MIL-STD-1553B operates at a fixed 1 Megabit per second (1 Mbps). It uses a time-division multiplexing scheme and a command/response protocol managed by the Bus Controller.

Question 3

In a MIL-STD-1553B network, which device is responsible for managing and initiating all data transfers on the bus?

Accepted Answer

Bus Controller (BC)

Answer

The Bus Controller (BC) initiates all transactions on a MIL-STD-1553B bus. Remote Terminals (RTs) respond only when commanded by the BC. The Bus Monitor (BM) passively records traffic without participating in transfers.

Question 4

How many bits are contained in each ARINC 429 data word?

Accepted Answer

32 bits

Answer

Each ARINC 429 transmission consists of a 32-bit word, divided into a label field (bits 1–8), a source/destination identifier (bits 9–10), data field (bits 11–28), sign/status matrix (bits 29–30), and a parity bit (bit 32).

Question 5

What is the primary advantage of ARINC 664 (AFDX — Avionics Full-Duplex Switched Ethernet) over ARINC 429 in modern aircraft?

Accepted Answer

Vastly higher bandwidth and bidirectional data flow on a single connection

Answer

ARINC 664/AFDX provides 10/100 Mbps full-duplex bandwidth, supporting bidirectional communication over a single connection — a dramatic improvement over ARINC 429's 12.5 kbps or 100 kbps unidirectional bus. It is used in aircraft such as the Airbus A380 and Boeing 787.

(AET) Aircraft Electronics Technician Practice Test

(AET) Aircraft Electronics Technician Practice Test

AET Data Bus Systems and Protocols