Airframe Structures

Aircraft Structure and Maintenance

• ATA Zone 100 refers to the lower fuselage (below floor)
• Bonding lead to a remote aircraft component must be 0.5 in wide
• An I-beam is subjected to bending, with different parts subject to tension (upper boom) and shear (the web)
• A radome is protected from static electricity build-up by conductive paint
• Precise points are located on an aircraft by a system of frame stations, water lines, and buttock lines
• A stringer is an example of a fail-safe structure
• Damage tolerant design allows for certain damage to the structure to go un-repaired between scheduled maintenance
• In the ATA 100 zonal system, the passenger entry door will have a designation of 800
• The pressure cabin is subject to hoop stress
• Shear stress is described as slipping away under the action of forces
• The ground cable must be a single strand copper wire 0.5 in cross-sectional area
• FS245, RWS45 refers to a point 245 inches from the datum line of the aircraft and 45 inches from the centreline of the right wing
• The radome is protected from lightning strike by diverter strips
• When shorting the two prongs with the single prong of a bonding tester together, the gauge will read zero

Materials and Structures

• Tension is the stress of elongating or stretching
• A fuselage station is a longitudinal point on the aircraft fuselage
• Composite materials are bonded by special paint
• Semi-monocoque construction offers good damage resistance
• Wing stations are measured outboard from the fuselage centreline
• A tie rod is designed to accept tensile loads
• Primary structure has multiple load paths, making it a fail-safe design
• A redundant structure is a fail-safe structure

Safety and Airworthiness

• Airworthiness requirements for large aircraft are found in CS 25
• An Anthropomorphic Test Dummy (ATD) is used to test aircraft structure and seating mount points for structural integrity
• The bonding lead to a remote aircraft component must be 0.5 in wide

Measurement and Location Systems

• Fuselage station numbers are measured in inches from the front of the aircraft

• Water Lines (WLs) are measured points on a vertical line

• Buttock lines are measurements from the centre line

• Lateral stations have station zero at the centre line### Aircraft Structures Classification

• Secondary structures are lightly stressed parts of the airframe, such as fairings, wheel shields, and minor component brackets, that will not cause failure of the aircraft if damaged.

Redundancy in Aircraft Structures

• A structure with built-in redundancy is called failsafe, meaning it can still function even if one part fails.

Stress and Material Properties

• Stress is the load per unit area acting on a material.
• Stress can cause deformation of a material, but it is not the same as deformation.

Structure Replacement and Classification

• A piece of structure that must be replaced at a specified number of cycles, flying hours, or years, regardless of its physical condition, is classified as safe-life.
• If a structure classification is unclear, it should be upgraded to primary as a precaution.

Safe-Life and Structural Failure

• Safe-life is the maximum number of flying hours that should elapse before a major structural failure occurs.

Bending Stresses

• Bending stresses are a combination of tension and compression stresses.

Airworthiness and Structural Surveys

• The Airworthiness Notice that refers to structural surveys is Notice 89.
• Structural survey inspections are normally called up by the manufacturer.

Wing Station Measurement

• Wing stations are measured from the Butt Line (BL).

Zonal Locations

• Zone 323 is located at the tip of the vertical stabilizer.