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Sample SACAA AME Avionics Practice Questions
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1Which digital logic gate produces a HIGH (1) output state ONLY when all of its input signals are in the HIGH (1) state?
A.OR gate
B.AND gate
C.NAND gate
D.NOR gate
Explanation: An AND gate is a fundamental digital logic gate that outputs a logic HIGH (1) if and only if all of its inputs are simultaneously HIGH (1). If any input is LOW (0), the output is LOW (0).
2According to De Morgan's laws, a NOR gate with inputs A and B is logically equivalent to which gate configuration?
A.An AND gate with inverted inputs (NOT A AND NOT B)
B.An OR gate with inverted inputs (NOT A OR NOT B)
C.A NAND gate with non-inverted inputs
D.An XOR gate with inverted inputs
Explanation: De Morgan's first law states that NOT (A OR B) = (NOT A) AND (NOT B). Therefore, a NOR gate is logically equivalent to an AND gate whose inputs have been inverted.
3What is the primary function of a D (Data/Delay) Flip-Flop in avionics digital logic circuits?
A.To multiply binary numbers
B.To store a single bit of digital data and transfer it to the output on an active clock edge
C.To convert analog voltage into a digital pulse train
D.To invert incoming digital signals continuously
Explanation: A D flip-flop captures the logic level present on its D input at the precise moment of an active clock transition (rising or falling edge) and holds that state at its output Q until the next active clock edge, functioning as a 1-bit memory cell.
4What is the standard total bit length of a single ARINC 429 digital data bus word?
A.16 bits
B.24 bits
C.32 bits
D.64 bits
Explanation: An ARINC 429 word consists of exactly 32 bits, divided into functional fields: Label (bits 1-8), SDI (bits 9-10), Data (bits 11-29), SSM (bits 30-31), and Parity (bit 32).
5Which bit position in a standard ARINC 429 word is designated for error detection parity, and what is the standard parity convention used?
A.Bit 1, Even Parity
B.Bit 8, Even Parity
C.Bit 32, Odd Parity
D.Bit 30, Odd Parity
Explanation: Bit 32 is the MSB of the ARINC 429 word and is reserved for Parity. The ARINC 429 standard specifies Odd Parity, meaning bit 32 is set to 0 or 1 such that the total number of logic 1s in the 32-bit word is odd.
6In fiber optic cables used for aircraft data links, what must be the relationship between the refractive index of the core (n1) and the cladding (n2) to achieve total internal reflection?
A.The refractive index of the core (n1) must be greater than the cladding (n2)
B.The refractive index of the cladding (n2) must be greater than the core (n1)
C.The refractive indices n1 and n2 must be exactly equal
D.The core refractive index must be zero
Explanation: Total internal reflection inside an optical fiber occurs only when light propagates from a medium of higher refractive index (n1, the core) toward a medium of lower refractive index (n2, the cladding) at an angle of incidence greater than the critical angle.
7In an ARINC 429 BNR (Binary) word, what information is conveyed by the Sign/Status Matrix (SSM) located at bits 30 and 31?
A.Hardware bus speed and label direction
B.Operating status such as Normal Operation (NO), Failure Warning (FW), No Computed Data (NCD), or Functional Test (FT)
C.Transmitter physical address and receiver pin assignment
D.Checksum count for error correction
Explanation: Bits 30-31 of an ARINC 429 word form the Sign/Status Matrix (SSM). For BNR data, SSM codes indicate status: 00 = Failure Warning, 01 = No Computed Data, 10 = Functional Test, and 11 = Normal Operation (plus sign/direction indications depending on parameter type).
8What are the standard data transmission bit rates defined by the ARINC 429 specification for High-Speed and Low-Speed operation?
A.High-Speed = 1 Mbps, Low-Speed = 100 kbps
B.High-Speed = 100 kbps, Low-Speed = 12.5 to 14.5 kbps
C.High-Speed = 10 Mbps, Low-Speed = 1 Mbps
D.High-Speed = 500 kbps, Low-Speed = 64 kbps
Explanation: ARINC 429 defines two operational speeds: High-Speed at 100 kbps (+/- 1%) and Low-Speed in the range of 12.5 to 14.5 kbps (+/- 1%).
9Which signal modulation format and voltage waveform characteristics are used on an ARINC 429 twisted shielded pair transmission line?
A.NRZ (Non-Return-to-Zero) with 0V and +5V TTL logic levels
B.Bipolar RZ (Return-to-Zero) with differential +10V (HI), 0V (NULL), and -10V (LO) nominal levels
C.Manchester II biphase encoding with 0V to +3.3V differential swing
D.PWM (Pulse Width Modulation) with +28V DC pulses
Explanation: ARINC 429 uses Bipolar Return-to-Zero (RZ) signaling over a twisted shielded pair. Line A relative to Line B swings +10V +/- 1V for a logic HIGH ('1'), -10V +/- 1V for a logic LOW ('0'), and 0V +/- 0.5V for a NULL state between bits.
10How is the 8-bit Label field (bits 1 through 8) transmitted on the wire in an ARINC 429 data word?
A.Bit 1 first (MSB first)
B.Bit 8 first (LSB of the label transmitted first)
C.Bits 1 through 8 simultaneously on 8 parallel lines
D.Bit 32 first, followed by Label bits in reverse order
Explanation: ARINC 429 transmits the Label field (bits 1-8) in reverse bit order compared to the rest of the word: bit 8 is transmitted first on the wire, followed by bit 7, bit 6 down to bit 1. The remaining bits 9-32 are transmitted LSB to MSB in numerical order.
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