Part-66 Module 13 Study Guide: Preparing for the B2 Aircraft Systems Exam

Module 13 covers the aircraft systems that enable navigation, communication, automatic flight, monitoring and crew alerting. The examination tests more than component recognition, requiring you to understand system inputs, outputs, operating modes, interactions and responses to failures.

Before beginning your revision, check the current EASA Part-66 aircraft maintenance licence requirements and confirm the applicable syllabus with your competent authority.

What is Module 13?

Part-66 Module 13 covers aircraft aerodynamics, structures and systems at the avionic level for B2 applicants. In practical terms, it focuses on how aircraft systems operate, interact and provide information to flight crew and maintenance personnel.

The exact syllabus and examination arrangements depend on the applicable Part-66 requirements and competent authority. Always study from the current official syllabus. Training notes and question banks are useful, but they are not a substitute for checking the latest regulatory material. UK candidates should also consult the UK CAA aircraft maintenance engineer licensing guidance.

Module 13 commonly includes:

• Flight control systems
• Autoflight and automatic landing
• Communication and navigation systems
• Flight instruments and electronic displays
• Inertial reference and air data systems
• Electrical and electronic systems
• Warning and recording systems
• Aircraft information systems
• Cabin and communication-related systems
• Maintenance and built-in test functions
• Digital techniques and system integration

You need to understand what happens when systems are selected, when signals are lost and when the aircraft changes from normal operation to an alternative or degraded mode.

If you are still building your foundation, our Ultimate Exam Guide for Part-66 Engineers provides additional context on licence examinations and preparation.

Why Module 13 is difficult

Module 13 tests systems thinking rather than isolated memory. You may know the function of the autopilot, autothrottle and VNAV, but the examination may ask which modes are compatible under a particular set of conditions, or what happens when one input becomes invalid.

The main challenges are:

• Similar-looking answer options
• Mode logic and mode compatibility
• Automatic changes following failures
• Sensor inputs and computer outputs
• Differences between normal, alternate and degraded modes
• Acronyms and system-specific terminology
• Questions based on aircraft-system principles rather than one specific aircraft type

Learn the logic behind each system. Memorising isolated answers is unreliable because a small change in wording can alter the correct response.

The major Module 13 subjects to revise

1. Autoflight systems

Autoflight is one of the most important areas in Module 13. Understand the relationship between:

• Flight director
• Autopilot
• Autothrottle or autothrust
• Flight management system
• Mode control panel or flight control unit
• Air data and inertial reference systems
• Radio navigation receivers
• Localiser and glideslope inputs
• Servo actuators and trim systems

Study the information flow rather than treating each unit as an isolated component:

1. Sensors and navigation receivers provide data.
2. Computers process that data.
3. The flight director calculates commands.
4. The autopilot may follow those commands.
5. The autothrottle controls thrust or speed.
6. The displays show selected and active modes to the crew.

Examination questions often focus on what is selected, what is active and what happens if an input disappears.

Autothrottle and autopilot mode compatibility

Some Module 13 question material asks which autopilot modes are compatible with autothrottle selected in SPEED mode. The expected answers may include IAS HOLD and ALT ARM. Other questions may identify HDG and V/S HOLD as incompatible combinations.

Do not rely on these combinations without checking the approved training material. The exact logic varies between aircraft. The underlying principle is that speed, altitude, vertical speed, heading and navigation modes assign different control responsibilities to pitch, roll and thrust.

When revising autoflight, relate each function to its input and controlled output:

• Heading: magnetic or inertial reference, controlled through roll.
• Vertical speed: air data and inertial data, controlled through pitch.
• Indicated airspeed: air data, controlled through pitch, thrust or both.
• Altitude: air data and altitude reference, normally controlled through pitch.
• Navigation tracking: radio or FMS guidance, controlling roll and, where applicable, pitch.
• Autothrottle speed mode: air data and a selected target, controlling engine thrust.

2. Autoland and approach modes

Automatic landing questions combine several systems. Revise:

• Localiser capture
• Glideslope capture
• Approach mode
• Flare mode
• Roll-out mode
• Radio altimeter inputs
• Redundancy and fail-operational operation
• Fail-passive operation
• Automatic go-around logic
• System degradation after loss of navigation signals

In a typical question, a go-around initiated after autoland selection requires the aircraft to increase speed and rotate nose up. The exact flight-control and thrust response depends on the aircraft system, but the principle is to establish the required climb attitude and thrust or speed condition.

Questions about localiser loss during final approach test the system's degradation logic. The correct response depends on the aircraft and the wording. Revise the difference between:

• Continuing an approach automatically after a single failure
• Completing the approach but requiring pilot intervention for landing
• Disconnecting the system or initiating a go-around

VNAV selection

Some training material states that VNAV can be selected only when the autopilot and flight director are selected. Check the terminology and engagement conditions used by your approved course material, because aircraft systems distinguish between VNAV availability, selection and engagement.

3. Flight control systems and fly-by-wire

For B2 candidates, fly-by-wire is a major subject. Understand:

• Pilot control inputs
• Flight control computers
• Control law changes
• Electrical signalling
• Hydraulic or electrical actuation
• Position feedback
• Redundancy
• Reversion modes
• Protections and limitations
• Maintenance indications and fault recording

In a fly-by-wire system, the control position is converted into an electrical signal and processed by flight control computers. The computers then command actuators and monitor feedback from the control surfaces.

A typical question asks how pitch and roll control positions are detected. The answer given in some study material is LVDTs, or Linear Variable Differential Transformers, used to measure linear displacement and provide position feedback. Learn both the abbreviation and the purpose of the device.

When revising sensors, ask:

• What physical quantity is being measured?
• Is the measurement linear or rotary?
• Does the sensor provide pilot input, surface position or system feedback?
• What happens if the signal is invalid?
• Are multiple channels compared?
• Does the system reject the input, downgrade its control law or generate a warning?

4. RVSM and altitude information

Reduced Vertical Separation Minimum operations depend on accurate altitude measurement, display and control. Some question material gives an expected tolerance of separation of ±80 feet.

Revise the wider system, including:

• Pressure altitude measurement
• Air data computers
• Altitude alerting
• Autopilot altitude capture and hold
• Transponder altitude reporting
• Independent altitude displays
• Static system integrity
• Altimeter accuracy and maintenance requirements

Understand what the value describes and how it relates to the equipment and monitoring required for RVSM operations.

5. Air data and inertial reference systems

Air data and inertial systems provide information used by most major avionics functions. Revise:

• Pitot and static pressure
• Total air temperature
• Air data computers
• Indicated airspeed
• Mach number
• Barometric altitude
• Vertical speed
• Angle of attack
• Inertial reference units
• Attitude and heading reference systems
• Accelerometers and gyroscopes
• Alignment
• Drift
• Redundancy and comparison monitoring

Understand how a blocked pitot tube differs from a blocked static port, and how the resulting information may affect displays, autoflight and warning systems.

For inertial systems, distinguish between measuring acceleration, measuring angular rate, calculating attitude, calculating position, providing heading and combining inertial information with radio or satellite navigation.

6. Navigation systems

Revise the principles and indications associated with:

• VOR
• DME
• ILS
• ADF
• Radio altimeter
• GNSS
• FMS
• Inertial navigation
• Weather radar
• Terrain awareness and warning systems
• Traffic alert and collision avoidance systems

Pay attention to the difference between the selected navigation source, tuned frequency, armed mode, captured mode, active mode, displayed deviation and system validity.

A mode may be armed but not active. A navigation source may be selected but invalid. A system may continue to display information while the associated guidance mode has disengaged.

7. Displays, warnings and central maintenance computers

Modern aircraft process, prioritise and distribute information. Understand the purpose of:

• Electronic flight instrument systems
• Primary flight displays
• Navigation displays
• Engine and system displays
• Electronic centralised aircraft monitoring
• Central warning systems
• Master caution and warning logic
• Central maintenance computers
• Fault messages
• Built-in test equipment
• Data buses and remote data concentrators

A central maintenance computer may collect faults from several aircraft systems, record them and present maintenance information to the crew or ground engineer.

Distinguish between a fault being detected, recorded, displayed as a maintenance message and presented as a crew warning. Not every recorded fault produces an immediate cockpit indication.

8. Communication systems

Revise both the equipment and the signal path. Typical subjects include:

• VHF communication
• HF communication
• Satellite communication
• Audio control panels
• Interphone systems
• Selective calling
• Emergency locator transmitters
• Passenger address systems
• Cabin interphone
• Data link communication
• Antennas and transmit-receive switching
• Static discharge and interference

Know how audio is selected, routed and prioritised. Also distinguish between communication, navigation, surveillance and data link functions. These may share antennas, control panels or computers, but their purposes are different.

9. Electrical and electronic system fundamentals

Although Module 13 is not Module 3, B2 candidates need sufficient electrical and electronic knowledge to understand aircraft-system operation. Revise:

• AC and DC distribution
• Transformer rectifier units
• Inverters
• Batteries
• External power
• Generators
• Busbars
• Contactors and relays
• Circuit protection
• Essential and emergency supplies
• Static electricity
• Electromagnetic interference
• Shielding and bonding
• Data buses
• Digital and analogue signals

For every system, ask:

1. What is the normal power source?
2. What is the alternate source?
3. What happens after a bus failure?
4. Which equipment is essential?
5. What indications show the failure?
6. Can the system shed loads or reconfigure automatically?

How to study Module 13 effectively

Start with the syllabus, not the question bank

Use question banks to become familiar with examination style, but do not treat them as your primary textbook. Begin with the current Module 13 syllabus and divide it into subject groups. Match each group with approved course material, training notes, diagrams, practice questions and your own condensed notes.

This approach prevents you from memorising answers without understanding the systems they describe. If you are considering formal training, use our Part 147 training schools resource to explore approved training options.

Build system diagrams

Draw the signal path for each major system. An autoflight diagram, for example, should show:

1. Sensors and receivers
2. Air data and inertial systems
3. Flight management and flight control computers
4. Flight director commands
5. Autopilot servos and autothrottle
6. Control surfaces and engine thrust
7. Position and performance feedback

Use the same method for ILS, fly-by-wire, flight displays, central maintenance computers, electrical power distribution, radio communication and navigation systems.

Make a mode-logic table

Create tables covering selected, armed and active modes, engagement conditions, disengagement conditions, compatible modes, incompatible modes and failure responses. Include VNAV selection, localiser and glideslope capture, autoland failure responses and go-around mode changes.

Check all terminology against the aircraft or training system used on your course. Mode names and engagement conditions can vary between manufacturers.

Learn what happens next

For every major system, practise answering:

• What happens when it is selected?
• What happens when it is engaged?
• What happens when an input is lost?
• What happens when one channel fails?
• What does the crew see?
• What does the maintenance computer record?
• What alternate source becomes available?
• Does the system continue, degrade or disconnect?

Treat numerical facts carefully

Create a separate list of numerical data, including the RVSM tolerance of ±80 feet. For each value, note what it describes, why it matters, which system uses it and whether it is a limitation, tolerance, threshold or performance value.

How to handle multiple-choice questions

Read the condition before the question

Words such as these can change the answer:

• Selected
• Armed
• Engaged
• Captured
• In speed mode
• During autoland
• At 400 feet
• After signal loss
• In degraded mode
• With autopilot selected
• With flight director selected

Read these conditions carefully. They often define the entire problem.

Eliminate physically or logically impossible answers

If a question asks what happens during an automatic go-around, an answer describing only a speed increase may be incomplete if the expected action also includes a nose-up rotation.

If a question concerns fly-by-wire position feedback, distinguish between pilot control input, flight control surface position, sensor type and feedback to the computer.

Be cautious with incomplete or duplicated material

Some old question banks contain duplicate options, incorrect lettering, truncated questions, outdated terminology or aircraft-specific answers presented as universal. If a question is incomplete, return to the system description and establish the actual failure logic rather than relying on the answer key.

A practical two-week revision plan

Days 1 and 2: Syllabus and system architecture

• Read the Module 13 syllabus.
• Divide it into subject groups.
• Identify weak areas.
• Review aircraft system architecture.
• Start a glossary of abbreviations.

Days 3 and 4: Autoflight

• Review the autopilot, flight director and autothrottle.
• Study selected, armed and active modes.
• Revise compatibility and incompatibility.
• Practise VNAV, approach and go-around questions.
• Draw the control loops.

Days 5 and 6: Flight controls and air data

• Revise conventional and fly-by-wire systems.
• Study LVDTs and position feedback.
• Review air data and inertial reference systems.
• Cover redundancy and reversion modes.

Days 7 and 8: Navigation

• Revise VOR, DME, ILS, ADF and GNSS.
• Study FMS and inertial navigation.
• Review radio altimeters and terrain systems.
• Practise signal-loss and invalid-data scenarios.

Days 9 and 10: Displays, warnings and maintenance computers

• Review electronic flight displays.
• Study warning priorities.
• Revise CMC and BITE functions.
• Distinguish between crew indications and maintenance messages.

Days 11 and 12: Communications and electrical systems

• Revise VHF, HF, satellite and cabin communication.
• Review electrical power sources and bus switching.
• Study essential and emergency supplies.
• Cover shielding, bonding and interference.

Days 13 and 14: Examination practice

• Complete timed question sets.
• Review every incorrect answer.
• Identify repeated errors.
• Return to the syllabus instead of repeating questions without analysis.
• Complete a final review of mode logic and numerical facts.

Final Module 13 checklist

Before sitting the B2 aircraft systems examination, make sure you can explain:

• The difference between autopilot, flight director and autothrottle
• The meaning of selected, armed and active modes
• Compatible and incompatible autoflight modes
• The conditions for VNAV selection
• What happens during an automatic go-around
• How autoland capability can degrade after a failure
• How fly-by-wire systems receive and monitor control-position information
• The role of LVDTs in position measurement
• The RVSM separation tolerance of ±80 feet
• The operation of air data and inertial reference systems
• The function of navigation receivers and FMS equipment
• How electronic displays and warning systems prioritise information
• The role of a central maintenance computer
• The difference between a recorded fault and a cockpit warning
• How aircraft communication systems route audio and data
• How electrical power is distributed and reconfigured
• Why redundancy, monitoring and failure logic matter

Final thoughts

Module 13 is challenging because it requires you to understand the aircraft as an integrated machine. Sensors feed computers, computers command actuators, displays report the result and maintenance systems record faults.

Use question banks, but verify every answer against reliable technical material. Draw diagrams, learn the logic behind autoflight and fly-by-wire, treat numerical values carefully and check any question that appears incomplete or aircraft-specific. For further aviation maintenance guidance and career insights, visit the AeroTech Careers Blog.

With a structured study plan and a clear understanding of system interactions, Module 13 is manageable.