Aircraft Maintenance Licence: Category B1 Knowledge Levels

Category B1 Licence and Knowledge Levels

• The Category B1 licence is governed by CASA B1-11b and includes Aeroplane Structures, Turbine Aeroplane Aerodynamics, and Systems.
• The knowledge levels for categories A, B1, and B2 are indicated by numerical indicators (1, 2, or 3) against each applicable subject.
• Category C applicants must meet either the category B1 or category B2 basic knowledge levels.

Knowledge Level 1

• Objectives:
  • Be familiar with basic elements of the subject
  • Give a simple description of the subject using common words and examples
  • Use typical terms

Knowledge Level 2

• Objectives:
  • Understand theoretical fundamentals of the subject
  • Give a general description of the subject using typical examples
  • Use mathematical formulae in conjunction with physical laws
  • Read and understand sketches, drawings, and schematics
  • Apply knowledge in a practical manner using detailed procedures

Knowledge Level 3

• Objectives:

  • Have a detailed knowledge of theoretical and practical aspects of the subject
  • Combine and apply separate elements of knowledge in a logical and comprehensive manner
  • Know the theory of the subject and interrelationships with other subjects
  • Give a detailed description of the subject using theoretical fundamentals and specific examples
  • Understand and use mathematical formulae related to the subject
  • Read, understand, and prepare sketches, simple drawings, and schematics
  • Apply knowledge in a practical manner using manufacturer's instructions
  • Interpret results from various sources and measurements and apply corrective action where appropriate### Airframe Structures - General Concepts

• Airworthiness requirements are derived from pertinent regulations, standards, and specifications (Level 2)

• There are three main categories of airworthiness requirements: Transport Category Aircraft, Structural Design Requirements, and Airworthiness Requirements for Structural Strength

• Transport Category Aircraft have specific requirements for structural strength, including those related to fatigue, damage tolerance, and durability

• Structural Design Requirements encompass factors such as safety, performance, and reliability

• Airworthiness Requirements for Structural Strength address issues like stress, strain, and fatigue in aircraft structures

• There are three approaches to structural design: safe-life, fail-safe, and damage-tolerant

• Safe-life design focuses on preventing failure, fail-safe design focuses on ensuring safety in the event of failure, and damage-tolerant design focuses on detecting and repairing damage

• Durability is a critical aspect of airworthiness, as it affects the long-term performance and safety of the aircraft

• Zonal and station identification systems are used to locate and identify specific areas of the aircraft

• There are several types of zones, including aircraft reference zones, major zones, subzones, and zones, each with its own reference datum

• Position identification and location systems are used to identify specific positions on the aircraft, including fuselage, wing, and engine positions

• Clock position is a method of identifying locations on the aircraft using a 12-hour clock face

Airframe Structures Loads and Forces

• Stress, strain, and fatigue are critical factors in aircraft structures
• Stress-strain curves are used to analyze the behavior of materials under different loads
• Tension, compression, shear, torsion, and bending are all types of loads that affect aircraft structures
• Hoop stress is a type of stress that occurs in circular structures, such as fuselage and wing sections
• Fatigue is a critical factor in aircraft structures, as it can lead to failure over time

Aircraft Drainage

• Corrosion is a major concern in aircraft systems, and drainage is critical to preventing corrosion
• Drainage systems are designed to remove water and other fluids from the aircraft
• Pressurized fuselage drain valves, drain holes, and ventilation systems are all used to manage drainage and prevent corrosion

System Installation Provisions

• System installation provisions are critical to ensuring the safe and reliable operation of aircraft systems
• Provisions include factors such as hydraulic systems, air conditioning systems, electrical/avionics systems, fuel storage, and main landing gear
• Waste disposal and potable water systems are also critical to aircraft operation

Lightning Strikes

• Lightning strikes are a major concern in aircraft operation, as they can cause significant damage and safety risks
• Aircraft are designed to withstand lightning strikes, and protection systems are used to prevent damage

Aircraft Electrical Bonding

• Bonding is critical to ensuring the safe and reliable operation of aircraft electrical systems
• Bonding leads are used to connect electrical components and prevent electrical shocks### Airworthiness Requirements
• An aircraft is airworthy only when it conforms to the regulations under which it has been certified
• Regulatory authorities work together closely to set uniform requirements
• Airworthiness standards are organized into sections, called parts, and each part deals with a specific type of activity
• Examples of airworthiness standards:
  • Part 23: Normal, Utility, Acrobatic, and Commuter Aircraft
  • Part 25: Transport Category Aircraft
  • Part 27: Normal Category Rotorcraft
  • Part 29: Transport Category Rotorcraft
  • Part 33: Aircraft Engines
  • Part 35: Propellers
  • Part 39: Airworthiness Directives
  • Part 43: Maintenance, Preventive Maintenance, Rebuilding, and Alteration
  • Part 65/Part 66: Aircraft Maintenance Engineer Licensing
  • Part 145: Aircraft Maintenance Organisations
  • Part 147: Aviation Maintenance Technicians Schools

Structural Design Requirements

• The structural design criteria are determined by the type of aircraft and its intended use
• The criteria must consider:
  • Manoeuvres
  • Speeds
  • Useful loads
  • Gross weights
  • Inadvertent manoeuvres
  • Effects of turbulent air
  • Severity of ground contact during landing
• Certification of airframe structure generally requires testing and/or analysis to demonstrate:
  • Static strength
  • Fatigue strength

Structural Classifications

• Primary structure: critical to the safety of the aircraft; examples include fuselage, wings, and horizontal and vertical stabilisers
• Secondary structure: failure may cause significant damage but not lead to loss of aircraft; examples include wing fixed leading and trailing edges, dorsal fin, and nose radome
• Tertiary structure: failure would not significantly affect the operation of the aircraft; examples include brackets, clamps, and mounting hardware

Fatigue Design Philosophy

• Fatigue considerations comprise an important part of aircraft structural design
• Three distinct design approaches:
  • Safe-life (safety by retirement): specifies a safe lifespan within which there is no significant risk of structural failure of a component
  • Fail-safe (safety by inspection): a structure should be able to sustain the limit load even when one of its elements has failed
  • Damage-tolerance (safety by inspection): a structure is able to sustain a given level of fatigue, corrosion, manufacturing defects or accidental damage and still withstand design loads without structural failure or excessive structural deformation for a predetermined period

Fail-Safe and Damage-Tolerance

• Fail-safe disadvantages:
  • Components are taken out of service even though they may have substantial remaining lives, creating unnecessary costs
  • Cracks sometimes occur prematurely, creating a safety problem
• Damage-tolerance:
  • Can be applied to a structure that is able to sustain a given level of fatigue, corrosion, manufacturing defects or accidental damage and still withstand design loads without structural failure or excessive structural deformation for a predetermined period
  • Uses testing and analysis to determine the critical crack length, residual strength, and inspection intervals
  • Non-destructive testing is used to detect cracks before they reach critical length

Durability

• Durability is the structure's ability to sustain degradation from sources such as fatigue, accidental damage, and environmental deterioration to the extent that they can be controlled by economically acceptable maintenance and inspection programs
• Durability of an aircraft structure comes from having a slow crack growth characteristic and the ability to contain or restrict the progress of damage