I85PREP
⌘ K
Part-66 Module 5 study materials
Part-66 Module 5 study resources

Part-66 Module 5 practice questions

One question at a time. Build your Part-66 Module 5 understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Electronic Instrument Systems

On a transport category aeroplane, the primary purpose of the EICAS is to display engine and system parameters to the crew, together with alerting messages. Which of the following best describes the function of EICAS?

  1. To present weather radar imagery on the navigation display
  2. To display engine and system parameters to the crew Correct answer.
  3. To control the lateral modes of the autopilot
  4. To compute the aircraft's position from radio aids

Explanation

EICAS (Engine Indication and Crew Alerting System) concentrates engine parameters, system status and caution/warning messages on the centre display units. Position computation and autopilot mode control are functions of the flight management and autopilot systems, and weather radar imagery is presented on the navigation display.

Question 2Electronic Instrument Systems

Which set of information is normally presented on the primary flight display of an EFIS equipped aeroplane?

  1. Attitude, airspeed and altitude Correct answer.
  2. Weather radar returns and terrain
  3. System synoptic diagrams
  4. Engine oil pressure and fuel flow

Explanation

The primary flight display gathers the flight-critical attitudes and pitot-static data, normally attitude, airspeed, altitude, heading and flight director or ILS guidance, into the pilot's central field of view. Engine parameters, radar and synoptics are shown on other display units.

Question 3Electronic Instrument Systems

In an aircraft electronic instrument system, ARINC 429 is best described as:

  1. A unidirectional digital data bus Correct answer.
  2. A bidirectional fibre-optic bus
  3. A cockpit voice and data recorder link
  4. An analogue synchro transmission system

Explanation

ARINC 429 carries 32-bit digital words in one direction only, from a single transmitter over a screened twisted pair to one or more receivers. It is not bidirectional, not analogue and not a recorder interface.

Question 4Electronic Instrument Systems

A liquid crystal display unit produces its image by:

  1. Deflecting an electron beam onto a phosphor screen
  2. Modulating backlight through liquid crystal cells Correct answer.
  3. Ionising gas in a matrix of small cells
  4. Rotating an array of micro-mirrors

Explanation

In an LCD the liquid crystal cells act as light valves that modulate light from a backlight, with colour filters and polarisers forming the image. There is no electron beam, no gas discharge and no moving mirror array in a standard LCD panel.

Question 5Electronic Instrument Systems

The purpose of standby attitude and airspeed indications on a glass cockpit aeroplane is to:

  1. Give the maintenance crew a quick system status check
  2. Provide attitude data if the main displays fail Correct answer.
  3. Act as the master reference for the autopilot
  4. Display engine parameters after a dual FADEC failure

Explanation

Standby instruments are an independent, self-contained means of providing attitude and pitot-static information if the electronic display system or its power supply is lost. They are not used for engine indication, maintenance status or as the autopilot reference.

Question 6Electronic Instrument Systems

On an EFIS aeroplane fitted with two symbol generators, failure of one symbol generator normally results in:

  1. The affected display units going blank with no recovery
  2. Reversion to standby instruments only, with no display recovery
  3. Total loss of all electronic displays
  4. Transfer of the affected displays to the remaining generator Correct answer.

Explanation

Symbol generator architectures are designed with redundancy so that the remaining generator can drive the displays of the failed channel, either automatically or by selection on the display select panel. Complete loss of all displays or permanent blanking would defeat that redundancy.

Question 7Electronic Instrument Systems

The flight mode annunciator at the top of the primary flight display shows:

  1. The thrust limit and target N1 for the engines
  2. Radio height and decision height annunciation
  3. The aircraft's position relative to the active waypoint
  4. The engaged and armed modes of the guidance systems Correct answer.

Explanation

The flight mode annunciator reports which autopilot, autothrust and flight director modes are engaged, armed or captured so that the crew can confirm the automation is doing what was selected. Waypoint position belongs to the navigation display, thrust limits to the engine display and radio height to the altitude area of the PFD.

Question 8Electronic Instrument Systems

In a typical EFIS installation, the display unit itself consists of:

  1. The symbol generator and the data bus couplers
  2. The EFIS control panel and the dimming sensor
  3. The screen plus its drive electronics Correct answer.
  4. The air data computer and the display screen

Explanation

The display unit is the line replaceable panel containing the screen, its drive and deflection or addressing electronics and the power supply needed to form a picture. The symbol generator, air data computer and control panel are separate units connected to it.

Question 9Electronic Instrument Systems

Selecting a higher range on the EFIS control panel causes the navigation display to:

  1. Change the display from rose to arc presentation
  2. Show a larger area of the map at a smaller scale Correct answer.
  3. Increase the number of weather radar echoes displayed
  4. Show a smaller area of the map at a larger scale

Explanation

The range selector sets the maximum distance represented by the outer edge of the display, so a higher range covers more ground with each pixel representing a greater distance. The number of echoes is set by the radar receiver, and rose or arc presentation is chosen by a separate mode selector.

Question 10Electronic Instrument Systems

Which of the following is supplied by the air data computer to the electronic display system?

  1. Engine N1, N2 and exhaust gas temperature from the FADEC
  2. Attitude, turn rate and body acceleration from the gyros
  3. Barometric altitude, heading and drift angle from the compass
  4. Airspeed, altitude, vertical speed and Mach number Correct answer.

Explanation

The air data computer processes pitot and static pressures and total air temperature to produce computed airspeed, pressure altitude, vertical speed, Mach number and temperature data. Heading and attitude come from the inertial and compass systems, and engine parameters come from the engine control units.

Question 11Electronic Instrument Systems

On an Airbus aeroplane, the ECAM system presents:

  1. Radio frequencies and ATC messages on the lower display
  2. Navigation and flight plan data on the outer display units
  3. Only engine parameters, with systems shown on the overhead panel
  4. Engine parameters and system synoptics on the centre displays Correct answer.

Explanation

ECAM uses the two centre display units, the upper one for engine and warning display and the lower one for system synoptic diagrams and status. Navigation and flight plan data appear on the outer navigation displays, and radio management is handled by a separate unit.

Question 12Electronic Instrument Systems

Compared with a cathode ray tube, an LCD display unit in the flight deck:

  1. Is lighter and needs no high-voltage supply Correct answer.
  2. Requires a higher anode voltage supply
  3. Is heavier but more resistant to vibration
  4. Has a shorter service life and a narrower angle

Explanation

LCD panels are flat, lighter and do not need the electron gun, high-voltage anode supply or heavy shielding of a CRT. They also offer a longer life and better resistance to the shock and vibration of the flight deck environment.

Question 13Electronic Instrument Systems

On an electronic engine indication display, an amber digital readout normally means:

  1. A value outside its normal limits Correct answer.
  2. An advisory message with no limits involved
  3. A value within the normal operating band
  4. An invalid or failed sensor input

Explanation

Colour coding on electronic engine displays uses amber for a parameter that has moved outside its normal operating limits and requires crew awareness, while green shows normal values and red indicates a limit exceedance. Invalid data is normally flagged by dashes or an amber boxed failure indication rather than a live amber value.

Question 14Electronic Instrument Systems

An AFDX network differs from ARINC 429 principally because AFDX:

  1. Transmits analogue synchro signals over screened cable
  2. Relies on token passing between all line units
  3. Uses a single twisted pair in one direction only
  4. Uses switched Ethernet with virtual links Correct answer.

Explanation

AFDX, defined in ARINC 664 Part 7, is a switched full-duplex Ethernet network in which virtual links guarantee bandwidth and timing, and redundant networks provide fault tolerance. ARINC 429 by contrast is a simple unidirectional serial bus using a single twisted pair per direction of data flow.

Question 15Electronic Instrument Systems

Within a 32-bit ARINC 429 word, the 8-bit label is used to:

  1. Identify the parameter contained in the word Correct answer.
  2. Indicate the sign and validity of the data field
  3. Provide single-bit parity for the word
  4. Carry the source and destination identifier

Explanation

The label is an 8-bit octal code that tells the receiver what parameter the word contains, so the same bus format can carry many different parameters. Sign and validity are conveyed by the sign/status matrix bits, the source/destination identifier occupies its own two bits, and parity is the single final bit.

Question 16Electronic Instrument Systems

A laser gyro inertial reference unit must be aligned before flight because alignment:

  1. Establishes the local vertical and true north Correct answer.
  2. Recharges the internal backup battery
  3. Synchronises the unit with the magnetic compass
  4. Verifies that the pitot and static ports are clear

Explanation

During alignment the inertial platform measures the local gravity vector and senses the Earth's rotation rate to determine true north, giving a valid attitude and heading reference. It does not test the pitot-static system, charge batteries or depend on the magnetic compass for its heading reference.

Question 17Numbering Systems and Data Conversion

Convert the binary number 1011 to its decimal equivalent.

  1. 13
  2. 9
  3. 15
  4. 11 Correct answer.

Explanation

Each binary digit carries a place value that doubles from right to left: 1, 2, 4, 8. Summing the place values where a 1 appears gives 8 + 2 + 1 = 11.

Question 18Numbering Systems and Data Conversion

The decimal number 25 expressed in binary is:

  1. 11011
  2. 11001 Correct answer.
  3. 10011
  4. 10101

Explanation

Subtracting the largest powers of two gives 16 + 8 + 1 = 25, so the 16, 8 and 1 columns hold a 1 and the rest hold 0. Reading the columns from most to least significant gives 11001.

Question 19Numbering Systems and Data Conversion

How many bits are contained in one byte?

  1. 32 bits
  2. 8 bits Correct answer.
  3. 16 bits
  4. 4 bits

Explanation

A byte is defined as a group of eight binary digits, which allows 256 different combinations. It can be split into two 4-bit nibbles, each of which maps directly to one hexadecimal digit.

Question 20Numbering Systems and Data Conversion

What decimal value does the octal number 17 represent?

  1. 17
  2. 7
  3. 14
  4. 15 Correct answer.

Explanation

Octal is base 8, so each position has a weight of a power of eight: 1 x 8 + 7 x 1 = 15. The digit 7 is valid in octal because octal digits only run from 0 to 7.

Question 21Numbering Systems and Data Conversion

In the hexadecimal system, which decimal value does the symbol C represent?

  1. 12 Correct answer.
  2. 10
  3. 13
  4. 15

Explanation

Hexadecimal uses sixteen symbols: 0 to 9 keep their decimal values, and the letters A to F represent ten to fifteen in order. Counting A = 10, B = 11, C = 12, the symbol C stands for twelve.

Question 22Numbering Systems and Data Conversion

The binary number 1101 0111 is equal to which hexadecimal value?

  1. D7 Correct answer.
  2. D6
  3. B7
  4. 7D

Explanation

A hexadecimal digit maps to exactly four binary bits, so the byte is split into the nibbles 1101 and 0111. The first nibble 1101 is 13 (D) and the second 0111 is 7, giving D7.

Question 23Numbering Systems and Data Conversion

In an 8-bit two's-complement system, the binary pattern 0000 1010 (+10) is negated to give:

  1. 1000 1010
  2. 1111 0110 Correct answer.
  3. 1111 0101
  4. 0000 1010

Explanation

Negating in two's complement means inverting every bit and then adding 1. Inverting 0000 1010 gives 1111 0101, and adding 1 gives 1111 0110, which represents -10.

Question 24Numbering Systems and Data Conversion

The decimal number 47 expressed in binary-coded decimal (BCD) is:

  1. 0100 1011
  2. 0111 0100
  3. 0010 1111
  4. 0100 0111 Correct answer.

Explanation

In BCD each decimal digit is coded separately in a 4-bit group, so 4 becomes 0100 and 7 becomes 0111. Joining the two groups gives 0100 0111.

Question 25Numbering Systems and Data Conversion

Adding the binary numbers 1011 and 0110 gives:

  1. 10001 Correct answer.
  2. 11001
  3. 10011
  4. 10101

Explanation

In decimal the sum is 11 + 6 = 17, which is 10001 in binary. Column by column the addition produces a carry out of the 1s, 2s and 4s columns, leaving a final carry into the 16s column.

Question 26Numbering Systems and Data Conversion

The hexadecimal number 2A converted to decimal is:

  1. 42 Correct answer.
  2. 52
  3. 26
  4. 36

Explanation

Each hexadecimal place is a power of sixteen, and A stands for 10. The value is therefore 2 x 16 + 10 x 1 = 42.

Question 27Numbering Systems and Data Conversion

Which statement describes a defining property of Gray code?

  1. successive values differ by only one bit Correct answer.
  2. it can represent each decimal digit as a single digit
  3. it eliminates errors in serial data transmission
  4. it requires fewer bits than the equivalent binary number

Explanation

In Gray code, each step from one value to the next changes exactly one bit position. This limits the ambiguity of a reading taken while several bits are changing at once, which is why it is used in rotary encoders and position sensors.

Question 28Numbering Systems and Data Conversion

The standard ASCII character code represents each character using how many bits?

  1. 7 bits Correct answer.
  2. 6 bits
  3. 4 bits
  4. 16 bits

Explanation

Standard ASCII is a 7-bit code, which gives 128 distinct character codes covering the upper and lower case alphabet, digits and control characters. An eighth bit is sometimes added as a parity or extension bit but is not part of the basic code.

Question 29Numbering Systems and Data Conversion

In a system using even parity, a data byte contains five 1s. What value must the parity bit take?

  1. 1 Correct answer.
  2. 2
  3. 5
  4. 0

Explanation

Even parity requires the total number of 1s, including the parity bit, to be an even number. Since the data already contains five 1s, an odd count, the parity bit must be 1 to bring the total to six.

Question 30Numbering Systems and Data Conversion

The 8-bit two's-complement pattern 1111 0001 represents which decimal value?

  1. -14
  2. 241
  3. -16
  4. -15 Correct answer.

Explanation

Because the most significant bit is 1, the value is negative. Inverting 1111 0001 gives 0000 1110 (14) and adding 1 gives 15, so the pattern represents -15.

Question 31Numbering Systems and Data Conversion

The binary number 1101.101 expressed in decimal is:

  1. 13.25
  2. 12.625
  3. 13.5
  4. 13.625 Correct answer.

Explanation

To the left of the point the values are 8 + 4 + 1 = 13. To the right the place values halve each step, giving 1/2 + 0 + 1/8 = 0.625, so the full value is 13.625.

Question 32Numbering Systems and Data Conversion

The octal number 345 converted to hexadecimal is:

  1. E3
  2. D5
  3. C5
  4. E5 Correct answer.

Explanation

First convert to decimal using powers of eight: 3 x 64 + 4 x 8 + 5 = 229. Dividing 229 by 16 gives 14 remainder 5, and 14 is the hexadecimal digit E, so the result is E5.

Question 33Data Buses

What are the two standard transmission bit rates defined for ARINC 429?

  1. 1 Mbit/s and 10 Mbit/s
  2. 1 kbit/s and 10 kbit/s
  3. 12.5 kbit/s and 100 kbit/s Correct answer.
  4. 155 kbit/s and 1 Mbit/s

Explanation

ARINC 429 defines two operating speeds, a low speed of 12.5 kbit/s and a high speed of 100 kbit/s, with the high speed being the norm on transport aircraft. The bit rate is fixed for a given bus and is not negotiated between terminals.

Question 34Data Buses

How is an ARINC 429 bus configured?

  1. A ring in which every terminal repeats the signal to the next
  2. Bidirectional, with any connected terminal able to transmit at any time
  3. A single transmitter feeding one or more receivers, with data flowing one way only Correct answer.
  4. Two transmitters sharing a common pair and resolving collisions

Explanation

ARINC 429 is a simplex, unidirectional bus: one transmitting LRU drives a twisted pair that may feed up to 20 receivers. Where two-way exchange is needed, two separate buses are installed, one for each direction. There is no arbitration because only one transmitter exists on a bus.

Question 35Data Buses

On a CAN bus, a dominant bit is represented by which logic state?

  1. Logic 0 Correct answer.
  2. Logic 1
  3. A floating high-impedance level
  4. Alternating polarity on successive bit times

Explanation

CAN is defined so that the dominant state corresponds to logic 0 and the recessive state to logic 1. Because a dominant bit overrides a recessive one, a node sending 0 wins arbitration against a node sending 1. This convention underpins both arbitration and error signalling.

Question 36Data Buses

Which property makes fibre-optic cable attractive for aircraft data buses?

  1. It is immune to electromagnetic interference Correct answer.
  2. It removes the need for any protocol on the bus
  3. It uses simple, low-cost copper connectors throughout
  4. It can deliver electrical power to remote units along the same cable

Explanation

Optical fibres carry light rather than current, so they neither pick up nor radiate electromagnetic energy; this makes them inherently immune to EMI and free from crosstalk. They also provide galvanic isolation between terminals. Power must still be supplied by separate wiring.

Question 37Data Buses

The label field of an ARINC 429 word occupies how many bits?

  1. 10
  2. 8 Correct answer.
  3. 4
  4. 16

Explanation

Each ARINC 429 word is 32 bits long and begins with an 8-bit label that identifies the parameter being transmitted. The remaining bits carry the source/destination identifier, the data, the sign/status matrix and a parity bit.

Question 38Data Buses

An ARINC 429 word uses odd parity. If the first 31 bits contain 12 ones, what must the parity bit be?

  1. 1, because 12 is below the mid-point of 16
  2. 1, making the total number of ones odd Correct answer.
  3. 0, because the total must then be even
  4. 0, so that the count remains at 12

Explanation

Odd parity requires the total number of ones in the 32-bit word, including the parity bit, to be odd. With 12 ones already present, the parity bit must be 1 to give 13. Setting it to 0 would leave an even count and be flagged as a parity error at the receiver.

Question 39Data Buses

ARINC 664 Part 7 (AFDX) is derived from which underlying technology?

  1. A controller area network using 11-bit identifiers
  2. A 1 Mbit/s command/response bus using Manchester coding
  3. Switched Ethernet operating at 100 Mbit/s Correct answer.
  4. A 12.5 kbit/s simplex bus carrying 32-bit words

Explanation

AFDX builds on full-duplex 100 Mbit/s switched Ethernet, adding virtual links, bandwidth allocation gaps and redundancy management to give deterministic timing. Frames are standard Ethernet frames with an added sequence number. This distinguishes it clearly from the older simplex and command/response buses.

Question 40Data Buses

MIL-STD-1553B transmits data at which rate, and using which line coding?

  1. 1 Mbit/s, using Manchester II bi-phase Correct answer.
  2. 100 kbit/s, using bipolar return-to-zero
  3. 2 Mbit/s, using pulse-width coding
  4. 10 Mbit/s, using 8B/10B coding

Explanation

MIL-STD-1553B operates at 1 Mbit/s over a shielded twisted pair, using Manchester II bi-phase encoding so that each bit has a mid-bit transition and the signal is self-clocking. Words are 20 bit times long, comprising a 3-bit sync, 16 data bits and a parity bit.

Question 41Data Buses

Why are terminating resistors fitted at each end of a CAN bus?

  1. To limit the current drawn by each connected node
  2. To provide a DC return path for the recessive state
  3. To raise the bus voltage above the transceiver threshold level
  4. To absorb the signal energy and prevent reflections Correct answer.

Explanation

A transmission line must be terminated in its characteristic impedance, typically 120 ohms at each end of a CAN bus, so that the travelling wave is absorbed rather than reflected. Reflections would otherwise superimpose on later bits and corrupt the bit levels. The parallel combination also presents the correct load to the transceivers.

Question 42Data Buses

Compared with RS-232, what is a characteristic of RS-485?

  1. It can connect only two devices, point to point
  2. It uses optical fibre as its standard medium
  3. It is differential, multi-drop, and suits long cable runs Correct answer.
  4. It is single-ended and normally limited to about 15 metres of cable

Explanation

RS-485 uses a balanced differential pair, which rejects common-mode noise and allows cable runs of up to roughly 1200 metres and many nodes on one bus. RS-232, by contrast, is single-ended, limited to short runs and intended for two devices. The differential nature is the key reason for its greater noise immunity and reach.

Question 43Data Buses

In an ARINC 429 word, what do the two sign/status matrix (SSM) bits indicate?

  1. The bit rate in use on that bus
  2. The validity and sign of the data in that word Correct answer.
  3. The parity of the preceding word
  4. The identity of the transmitting terminal

Explanation

The SSM bits tell the receiver how to interpret the data field, for example whether the value is positive or negative, or whether it is a valid computed value, a no-computed-data condition or a failure warning. They therefore act as a built-in health and sign indicator for each parameter.

Question 44Data Buses

Why are the two wires of a signal pair twisted together with a defined pitch?

  1. To make the cable stiffer and easier to route along the aircraft frames
  2. To increase the capacitance between the pair and so filter out high-frequency noise
  3. To allow the same pair to carry both the signal and a DC supply
  4. To equalise the pickup in both wires so that induced noise cancels Correct answer.

Explanation

Twisting ensures that both conductors occupy nearly the same positions relative to any interfering field, so the same noise voltage is induced in each. Because the receiver responds only to the difference between the wires, the common-mode noise cancels. The defined pitch also controls crosstalk between adjacent pairs.

Question 45Data Buses

Two CAN nodes start transmitting at the same instant. Which frame wins arbitration?

  1. The one with the highest numerical identifier
  2. Whichever node has waited longest since its last transmission
  3. The one with the lowest numerical identifier Correct answer.
  4. The node with the greatest number of data bytes

Explanation

During arbitration each node compares the bit it sends with the bus level; a node sending a recessive 1 while another sends a dominant 0 loses and withdraws. A numerically lower identifier contains more leading dominant bits, so it wins. This gives identifiers an implicit priority without any loss of data.

Question 46Data Buses

An AFDX end system transmits each frame on both redundant networks A and B. How does the receiving end system handle the two copies?

  1. It uses network A for data and network B only for acknowledgements
  2. It stores both copies until the end of the bandwidth allocation gap and compares them byte by byte
  3. It alternates between A and B on successive frames of the same virtual link
  4. It accepts the first valid copy and discards the duplicate using the sequence number Correct answer.

Explanation

AFDX redundancy management places a sequence number in each frame so that the receiver can recognise duplicates. The first frame with a valid integrity check and the next expected sequence number is passed on, and any later copy is discarded. This gives fault tolerance without adding latency by waiting for the second network.

Question 47Data Buses

In an ARINC 429 word, the data field occupies bits 11 to 29. How many data bits does this provide, and in what order are they transmitted?

  1. 18 bits, including the sign bit within the field
  2. 21 bits, including two spare bits at the top
  3. 19 bits, least significant bit first Correct answer.
  4. 16 bits, most significant bit first

Explanation

Bits 11 through 29 inclusive give 19 data bits, which can represent values to about one part in 524288. ARINC 429 transmits each field least significant bit first, so the receiver must reassemble the magnitude accordingly. The sign is not part of this field; it is carried in the SSM bits.

Question 48Data Buses

In ARINC 664, what does the bandwidth allocation gap (BAG) of a virtual link define?

  1. The maximum number of virtual links that may be configured in one end system
  2. The propagation delay budget allowed between the two redundant networks
  3. The number of retransmissions permitted before a frame is declared lost
  4. The minimum interval between consecutive frames on that virtual link Correct answer.

Explanation

The BAG is the minimum time between the first bits of two successive frames belonging to the same virtual link, and it is one of the parameters used to guarantee bandwidth and bounded latency. Together with the maximum frame size it determines the link's allocated bandwidth. Values are powers of two from 1 ms to 128 ms.

Question 49Logic Circuits

A two-input AND gate produces a logic 1 output only when:

  1. The two inputs are at opposite levels
  2. Both inputs are at logic 1 Correct answer.
  3. Both inputs are at logic 0
  4. At least one input is at logic 1

Explanation

An AND gate performs logical multiplication, so its output is 1 only for the single input combination 1·1. Any input at 0 forces the output to 0.

Question 50Logic Circuits

With its input held at logic 0, the output of a NOT gate is:

  1. 1 Correct answer.
  2. 0
  3. Undefined
  4. High impedance

Explanation

An inverter always produces the complement of its input, so an input of 0 yields an output of 1. A high-impedance state applies only to tri-state devices with an enable control.