How to Balloon a Drawing for FAI: Rules and Steps

The first time I watched a quality engineer balloon a 7-sheet aerospace drawing, it took over 5 hours. By balloon 60, the numbering had gotten inconsistent, three features from Sheet 5 were missing, and a GD&T callout was duplicated across two views.

Learning how to balloon a drawing for FAI correctly the first time saves hours of rework and prevents the customer from rejecting your FAI report on sight.

Ballooning is the bridge between the drawing and the inspection report. Each balloon is a numbered circle placed next to a feature on the drawing, and each number corresponds to a row in AS9102 Form 3. Without this link, the CMM inspector does not know which physical feature on the part corresponds to which measurement requirement.

We covered the overall Form 3 structure in AS9102 Form 1 vs Form 2 vs Form 3 explained. This guide focuses specifically on the ballooning process itself.

How to Balloon a Drawing for FAI: Before You Place a Single Balloon

Step 1: Read the Entire Drawing First

Do not start ballooning on Sheet 1 and work forward. Read the entire drawing first. This preview takes 15 to 20 minutes on a complex drawing but prevents the most common and most expensive ballooning error: discovering on Sheet 5 that a feature you ballooned on Sheet 2 is the same feature seen from a different view.

During the preview, make notes on:

How many sheets and which sheets contain unique geometry vs repeated views. On a 7-sheet bracket, Sheets 2 and 3 might show the main views, Sheets 4 and 5 might show cross-sections and details, Sheet 6 might show GD&T callouts, and Sheet 7 might show surface treatment designations. Knowing this layout before starting prevents surprises.

Where the general notes are.

Usually Sheet 1, but some drawings place additional notes on later sheets. Identify every note block.

Which features appear in multiple views. A bore visible in the Top view, Section A-A, and Detail H is one bore. Flag these during preview so you do not create duplicate balloons later.

Where the GD&T feature control frames are concentrated. Some drawings cluster GD&T on one sheet. Others scatter them across multiple sheets. Know where to find them all.

Where the surface treatment designations are. These are almost always on the last sheet and are the most commonly missed category in Form 3 preparation. We covered this problem in commonly missed specs on aerospace drawings.

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Step 2: Identify the Governing Standards

Before placing any balloons, confirm the tolerance standard from the general notes. Is it ISO 2768mk (European drawings) or ASME Y14.5 with drawing-specific general tolerance notes (Boeing and American OEM drawings)?

This matters for ballooning because:

On ISO 2768mk drawings, every untoleranced dimension gets a balloon because the blanket standard creates an implicit tolerance. We covered the size-dependent tolerance table in our guide on AS9102 Form 3 for ISO 2768mk drawings.

On Boeing PVS drawings, untoleranced dimensions are governed by specific notes (Note 8N, Note 9N) with different scope. Each untoleranced dimension must be classified into the correct note category before the tolerance can be applied. We covered this in AS9102 Form 3 for Boeing drawings.

Skipping this step means you might miss dozens of untoleranced dimensions that need balloons.

The Ballooning Process: Step by Step

Step 3: Balloon General Notes

Start with the general notes block, usually on Sheet 1. Each note that creates an inspectable or verifiable requirement gets a balloon. Notes that are purely informational (drawing scale, projection method) do not get balloons.

Notes that DO get balloons:

"General tolerances per ISO 2768mk." This establishes the blanket tolerance standard. Balloon it as characteristic 1 with a note in Form 3: "Governing standard: ISO 2768-1:1989 medium class, ISO 2768-2:1989 class K."

"Break all sharp edges 0.3 to 0.5mm." This is a verifiable manufacturing requirement. Balloon it.

"Surface finish per PS551170 unless otherwise specified." This establishes a default surface finish requirement. Balloon it.

"Anodize per MIL-A-8625 Type II Class 1 on surfaces marked Class 1." This creates a surface treatment requirement that will be verified. Balloon it.

Notes that DO NOT get balloons:

"Third angle projection." Drafting convention, not inspectable.

"Dimensions are in millimeters." Unit declaration, not a characteristic.

"This drawing supersedes revision C." Revision history, not inspectable.

"For reference only." Explicitly not a requirement.

Step 4: Balloon Dimensions Sheet by Sheet

Starting from the first sheet with geometry, work through each view systematically. For each dimension:

Explicitly toleranced dimensions. "62.0 +/-0.1" gets a balloon. The Form 3 row includes nominal (62.0), tolerance (+/-0.1), upper limit (62.1), lower limit (61.9).

Untoleranced dimensions governed by blanket tolerance. "305" on an ISO 2768mk drawing gets a balloon. The Form 3 row includes nominal (305), tolerance (+/-0.5 from ISO 2768-m table, over 120 to 400mm range), upper limit (305.5), lower limit (304.5), and a source note "[ISO 2768-m general tolerance]."

Limit dimensions. ".310/.315" gets a balloon. The Form 3 row shows the limit callout and the converted bilateral tolerance: nominal 0.3125, tolerance +/-0.0025.

Diameter and radius callouts. Each gets its own balloon. A through hole "Dia 4.5 x 6 places" can be treated as one balloon with a note "6 places" or as 6 individual balloons depending on the customer's preference. For FAI, most customers accept one balloon with a note indicating multiple locations, but all 6 must be measured and recorded.

Step 5: Balloon GD&T Feature Control Frames

This is where most errors occur. Each feature control frame gets one balloon. The rules:

One balloon per frame, not per datum. A positional tolerance of 0.010 referencing datums A, B, and C is one balloon. The Form 3 row reads: "Position 0.010 A|B|C." Do not create three separate rows.

Composite feature control frames get one or two balloons. A composite position frame (two rows in one box) can be treated as one balloon with two requirement lines, or as two separate balloons with the same reference location. Ask your customer's preference. Some OEMs (Boeing, Airbus) have specific guidance on this.

Datum features themselves. If a datum (say Datum A, the bottom surface) has an explicit dimensional requirement, it gets its own balloon for that dimension. The datum

identification does not need its own balloon unless the customer specifically requires it.

Profile tolerances. Profile of a surface with datum references is one balloon. Be careful with all-around profile callouts (indicated by a circle at the leader line bend). These apply to the entire profile and are one balloon, not one balloon per surface segment.

We covered GD&T inspection method assignment in AS9102 Form 3 GDT callout inspection method guide. Deciding the inspection method is closely linked to the ballooning step because the method affects how the characteristic is structured in Form 3.

If you would rather not do this by hand, here is how the current ballooning software options compare, and the wider FAI software field beyond ballooning.

Step 6: Balloon Surface Treatment and Process Requirements

Surface class designations (Class 1 anodization-critical, Class 2 standard) each get a balloon. These are verified by visual inspection or process certification and should appear as Form 3 rows with inspection method "Visual" or "Process Cert."

Edge treatment requirements (break all sharp edges, deburr, radius edges) that were captured as general notes in Step 3 do not need to be re-ballooned. If edge treatments appear on specific features with specific callouts different from the general note, those specific callouts get their own balloons.

Paint or coating thickness requirements get balloons if they specify measurable values (e.g., "primer thickness 0.3 to 0.5 mil").

Step 7: Deduplicate Across Views

After ballooning all sheets, this is the critical review step. Go through the entire set of balloons and identify features that appear in multiple views.

The method: for each balloon, ask "does this exact feature appear in another view on another sheet?" Check the dimension value, the location on the part, and the tolerance. If a bore shows as "Dia 9.0 G6" on Sheet 2 and the same bore is visible in Section A-A on Sheet 4 with the same dimension, it is one bore. Remove the duplicate balloon and keep the one in the view where the feature is shown most clearly (usually the view with the most associated GD&T).

On the 7-sheet bracket I analyzed, deduplication reduced the count from 229 raw data points to 120 unique features, then to 95 verified characteristics after removing title block repetitions, reference dimensions, and construction elements. We covered the counting methodology in what counts as a characteristic in AS9102 Form 3.

Step 8: Verify the Final Count

Cross-check your balloon count against the drawing complexity. Typical ranges:

Simple single-sheet part (10-20 dimensions, minimal GD&T): 15 to 30 balloons.

Medium 2-3 sheet part (30-50 dimensions, some GD&T): 40 to 65 balloons.

Complex 5-7 sheet part (100+ dimensions, heavy GD&T): 75 to 120 balloons.

If your count is far outside these ranges, investigate. Too many usually means duplicates or title block data in Form 3. Too few usually means missed untoleranced dimensions or missed GD&T from later sheets.

Balloon Placement Best Practices

Proximity. Place the balloon as close to the feature as possible. The leader line should clearly point to the specific feature being called out, not to the general area.

Avoid obscuring. Do not place balloons over dimension text, GD&T symbols, or other annotations. If the area is congested, extend the leader line to clear space.

Consistency. Use the same balloon size, font, and leader line style throughout the entire drawing package. Mixing styles looks unprofessional and raises questions during review.

Leader lines. Use thin leader lines (0.3-0.5pt) that do not dominate the drawing. The line should end with an arrow or dot touching the feature. Avoid crossing leader lines from different balloons.

Color. Many shops use red balloons on the drawing to distinguish them from the original black annotations. This is not required by AS9102 but it helps the reviewer quickly identify ballooned features vs original drawing content.

Common Ballooning Mistakes and How to Avoid Them

Skipping later sheets. By Sheet 5 of a 7-sheet drawing, the quality engineer has been at this for 3 to 4 hours. Attention drops. GD&T callouts on Sheet 6 and surface designations on Sheet 7 get missed. Fix: always do a dedicated final pass through every sheet after the initial ballooning, specifically looking for missed items.

Ballooning reference dimensions. Dimensions in parentheses are reference only and are not inspectable. Do not balloon them. If you are unsure whether a dimension is reference, check the general notes. Some drawings explicitly state "Dimensions in parentheses are for reference only."

Splitting GD&T into multiple balloons. A positional tolerance with three datum references is one balloon, not three. The Form 3 row captures the full datum reference frame in one entry.

Ballooning title block data. Part number, material, weight, revision level, and approval signatures belong in Form 1, not as Form 3 characteristics. Do not balloon them.

Inconsistent numbering across revisions. When the drawing is revised and the FAI is updated, keep original balloon numbers where possible. Add new numbers for new features. Renumbering everything breaks traceability to the previous FAI. We covered this in AS9102 Form 3 characteristic numbering rules.

No reference location in Form 3. Every balloon must have a reference location (sheet number, view name) recorded in the Form 3 row. Without this, the reviewer cannot find the characteristic on the drawing, which violates the Rev C traceability requirement.

How Long Should Ballooning Take?

Based on conversations with quality engineers at GE Aerospace, Collins Aerospace, Mahindra Aerostructures, and Sansera Engineering, the typical times for manual ballooning (including the corresponding Form 3 row creation) are:

Simple single-sheet part: 1 to 2 hours. Medium 2-3 sheet part: 2 to 4 hours. Complex 5-7 sheet part: 4 to 8 hours. Very complex multi-sheet with heavy GD&T: 8 to 16 hours.

These times include the balloon placement on the drawing AND the corresponding Form 3 row creation (nominal, tolerance, limits, designator, inspection method). The two tasks happen simultaneously because each balloon generates one Form 3 row.

We published detailed time breakdowns in our guide on how long does FAI preparation take in aerospace.

Mavlon Balloons and Extracts Simultaneously

Mavlon reads every sheet, identifies every inspectable characteristic, assigns sequential balloon numbers with reference locations, and outputs a pre-populated Form 3 with the full data for each balloon. The quality engineer receives both the characteristic list and the balloon mapping without placing a single circle manually. The 4 to 8 hour process becomes a 30-minute review.

Bring Your Drawing to a Demo to see your drawing ballooned and extracted.