Aircraft drawings communicate far more than external shape. When a technician needs to understand what lies beneath a skin panel, how a spar web is reinforced, or how fuel passages route through a manifold casting, ordinary orthographic views fall short. Sectional views and cross-section drawings solve that problem by showing the interior of a part or assembly as if it had been cut open and laid flat for inspection. For the Aviation Maintenance Technician (AMT), reading these drawings accurately is not optional — it is a core competency that directly affects the safety of every aircraft you touch.
This article explains what sectional and cross-section drawings are, the conventions that govern how they are drawn, how to interpret the symbols and lines you will encounter, and where these drawings appear in the day-to-day maintenance environment. It is grounded in the guidance provided by the FAA in the Aviation Maintenance Technician Handbook — General (FAA-H-8083-30).
Why Ordinary Views Are Not Enough
A standard orthographic projection gives you front, top, and side views of an object. These are excellent for showing external shape, overall dimensions, and the relationship between features you can see on the outside. However, aircraft structures are rarely simple solid blocks. Spars have flanges, webs, and lightening holes. Hydraulic actuators contain pistons, seals, and internal passages. Fuel manifolds route fluid through multiple intersecting bores. Trying to show all of these internal details with hidden (dashed) lines in a regular view quickly creates a cluttered, unreadable mess. A sectional view cuts through the complexity — literally — by imagining that a cutting plane slices through the object at a carefully chosen location and that everything between the viewer and that plane is removed. What remains is a clear, dimensioned picture of the interior.
How Sectional Views Work
The Cutting Plane
Every sectional view begins with a cutting plane line drawn on the view that shows where the imaginary cut is made. Per standard drawing conventions used in aviation technical illustrations, the cutting plane line is a thick, dark line — often drawn as a series of long dashes alternating with pairs of short dashes. Arrows at each end of the cutting plane line point in the direction the viewer is looking after the cut is made. These arrows are critically important: they tell you which half of the object you are looking at. A section labeled A-A on one view corresponds to a separate drawing (or an adjacent view) labeled Section A-A, showing exactly what you see when you look in the direction of those arrows.
Section Lining (Hatching)
In the resulting sectional view, any material that has actually been cut through is shown with section lining, also called hatching. These are thin, evenly spaced diagonal lines drawn at 45 degrees across the cut surfaces. Section lining serves two purposes: it identifies which portions of the drawing represent solid material that was sliced by the cutting plane, and it distinguishes those areas from open spaces, holes, or cavities that were already present inside the part. When an assembly drawing shows multiple separate parts that have been sectioned, each part's hatching is drawn at a different angle or with a different spacing so the boundaries between components remain visually clear.
Types of Sectional Views
Aviation drawings use several standard types of sections, each suited to a particular situation:
- Full section: The cutting plane passes completely through the object from one side to the other, and the entire near half is removed. This gives the most complete interior picture and is used when the internal geometry is complex throughout the part.
- Half section: The cutting plane removes only one quarter of the object, leaving the other three quarters intact. The result shows interior detail on one side and exterior shape on the other side of the same view. This is useful for symmetrical parts such as bulkheads or circular cross-members, because a single view communicates both inside and outside information without drawing two separate views.
- Broken-out section (partial section): Only a small, irregular portion of the exterior is broken away to expose a specific interior feature. A curved break line bounds the exposed area. This technique is used when the technician only needs to see one local detail — a bolt hole reinforcement, a fitting attachment, or a small internal passage — without redrawing the entire part.
- Revolved section: The cross-sectional shape of a feature (such as a spar cap, a rib, or a structural tube) is rotated 90 degrees and drawn directly on top of the longitudinal view at the location of the cut. This efficiently shows the profile of an elongated structural member without requiring a separate drawing sheet.
- Removed section: Similar to a revolved section, except the cross-sectional shape is drawn adjacent to the main view rather than superimposed on it. A centerline or leader line connects the removed section to its location on the main view. Removed sections are used when the cross-section is too complex or too small to be drawn clearly inside the main view.
Reading Cross-Section Drawings in Practice
A cross-section drawing is essentially a sectional view taken perpendicular to the longest axis of a component. When you look at a wing spar cross-section, for example, you are seeing a slice taken straight across the spar — a view that shows the exact shape of the upper and lower caps, the web thickness, any lightening holes, and any doublers or reinforcement plates. Similarly, a fuselage cross-section shows the frame shape, the skin thickness, and the arrangement of stringers around the circumference.
To use a cross-section drawing correctly, always begin by locating the cutting plane on the overall assembly or detail drawing. Confirm you are looking at the correct station — aircraft structures are often divided by fuselage stations (FS), wing stations (WS), or buttock lines (BL), and a cross-section drawing is meaningless unless you know precisely where along the structure it applies. The drawing title block and any station callouts in the vicinity of the cutting plane line will give you this information.
Next, identify what each hatched region represents. On a simple machined part this is straightforward. On a composite or bonded assembly, the drawing may use different hatch patterns or symbolic callouts to distinguish aluminum from steel, or metal from a honeycomb core. The drawing's material legend or notes block will decode these symbols. Never assume — always verify the material designation against the notes.
Dimensions on sectional views follow the same rules as on any other view. Dimension lines, extension lines, and leader lines point to the features being measured. Tolerances, finish marks, and weld symbols that apply to an interior surface are placed directly on the sectional view where that surface is visible, not on an exterior view where the surface would have to be shown as a hidden line.
Common Applications in Aircraft Maintenance
AMTs encounter sectional and cross-section drawings throughout maintenance documentation:
- Structural repair manuals (SRMs): Repairs to skins, spars, frames, and stringers are almost always defined with cross-section drawings that show doubler placement, fastener patterns, and the exact geometry of the repaired zone.
- Illustrated parts catalogs (IPCs): Exploded assembly drawings often include local sectional views to show how seals, snap rings, or bushings are installed in bores that would otherwise be invisible.
- Overhaul manuals: Hydraulic and fuel system component overhauls rely on full sections of actuator bodies and valve housings to show internal bore diameters, land widths, and port locations that dictate both reassembly procedure and inspection limits.
- Engineering orders (EOs) and service bulletins (SBs): Modifications that involve structural additions typically supply cross-section drawings to show how new members integrate with existing structure at each affected station.
Key Numbers and Rules
- Section lining is drawn at 45 degrees to the principal horizontal or vertical lines of the view as the standard angle; alternate angles (30° or 60°) are used when the part outline is itself close to 45° to avoid confusion.
- Adjacent parts in an assembly section use different hatch angles or spacing to differentiate them — never the same pattern touching each other.
- A cutting plane line takes precedence over a centerline when both occur at the same location on a drawing; the cutting plane is drawn as the dominant line.
- Features that are not sectioned even when the cutting plane passes through them include: bolts, rivets, screws, shafts, rods, ball bearings, keys, and webs of standard structural shapes. These are drawn in full (as solid exterior views) to avoid misleading cross-sections of fasteners.
- The section label letters (A-A, B-B, C-C, etc.) are assigned in alphabetical order from left to right or top to bottom on the drawing sheet.
Common Test Traps
- Arrow direction confusion: The arrows on the cutting plane line point toward the portion of the object you are looking at — not the portion being removed. Many students read them backward and end up interpreting the wrong half of the assembly.
- Hatching does not mean solid material throughout: Hatching only marks material that was cut by the cutting plane. An adjacent area that is not hatched inside the same outline is an internal cavity — this distinction is critical when verifying bore diameters or wall thicknesses.
- Fasteners are never sectioned: A bolt passing through a sectioned part is drawn as a complete, uncut bolt even though the cutting plane slices the surrounding structure. Marking through a fastener as if it were sectioned is an error the written test exploits.
- Revolved vs. removed sections: A revolved section is drawn on the view at the cut location; a removed section is drawn away from the view. They look similar but carry different implications for scale and orientation — read the title and connecting lines carefully.
- Ignoring station callouts: Using a cross-section drawing without confirming the fuselage or wing station it represents is a dangerous habit. A spar at FS 120 may have a very different cross-section from the same spar at FS 200; applying the wrong section can lead to incorrect repair dimensions.
Mastering sectional and cross-section drawings gives you a powerful window into structures and components you cannot see with your eyes alone. By learning to locate the cutting plane, interpret hatching, and read dimensions from interior surfaces, you develop the drawing literacy that every aircraft maintenance technician depends on for safe, accurate work.