Module 7.5-7.6 Engineering drawings, diagrams, standards, fits and clearances

Knowledge levels

Sub-module	A	B1 / B3	B2 / B2L
7.5 Engineering drawings, diagrams and standards	1	2	2
7.6 Fits and clearances	1	2	1

Types of drawing

Drawing	Purpose
Detail drawing	one part with all dimensions, material, finish
Assembly drawing	how parts fit together; parts list
Installation drawing	where an assembly is fitted on the aircraft
Sectional view	an imaginary cut showing internal features (hatched)
Exploded view	parts separated along their axes - used in illustrated parts catalogues (IPC)
Block diagram	functional relationship of units, no wiring detail
Schematic diagram	how a system works (flow of fluid or signals), components shown by symbols
Wiring diagram	actual wires, connectors, pin numbers, wire identifications, splices, ground points
Pictorial (isometric, oblique, perspective)	realistic 3-D impression

Projections

• Orthographic projection shows an object in several 2-D views (front, top, side).
• First-angle projection (European): the plan view is drawn below the front view; the left side view is drawn on the right. The projection method is identified by a small truncated-cone symbol in the title block.
• Third-angle projection (US/UK aircraft drawings): the plan view is drawn above the front view; the right side view on the right.
• Always check the projection symbol in the title block.