Boeing Coordination Hole (C/H) Tolerance Requirements: What Subcontractors Need to Know

If you have quoted a Boeing structural part, you have seen the designations C/H and P/H on the drawing. They appear next to hole callouts, usually with a note reference pointing back to a general tolerance block that defines what each classification means.

These are not optional annotations. They define two completely different manufacturing and inspection requirements for what might look like identical .100" diameter holes. Getting them wrong does not just fail inspection. It can cause assembly failures at the aircraft level.

This guide covers Boeing coordination hole tolerance requirements in full, from diameter limits to positional inspection

What Are Coordination Holes (C/H)?

Coordination holes are precision-located reference holes used during aircraft assembly to align structural components. When two or more parts are joined together on an aircraft fuselage, wing, or empennage, the coordination holes ensure that every part fits into the assembly jig in exactly the right position.

The word "coordination" is literal. These holes coordinate the position of the part relative to the assembly tooling and to mating parts. If a coordination hole is out of position by even a few thousandths of an inch, the part will not align correctly in the assembly fixture, and the downstream assembly process fails.

What Are Pilot Holes (P/H)?

Pilot holes are undersized starter holes that will be enlarged during the assembly process. They are drilled at the part manufacturing stage to establish hole location, but they are intentionally smaller than the final fastener hole size. During assembly, the pilot holes are match-drilled or reamed to final size through the mating parts, ensuring perfect alignment between the joined components.

Because the pilot hole will be enlarged later, its positional accuracy requirements are less stringent than a coordination hole. The hole just needs to be close enough for the assembly drill to find it.

BOEING TOLERANCES LEAVE NO ROOM FOR A MISS

Coordination hole tolerances are exactly where a missed spec fails a Boeing FAI. Mavlon extracts every one, hole, tolerance, and datum.

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Boeing Coordination Hole Tolerance Requirements: C/H vs P/H

Here is a typical Boeing general tolerance note for classified holes, taken from a structural fitting drawing:

Coordination Hole (C/H):

• Drill hole diameter: .100" ±.004"
• Positional tolerance: .010" diameter at MMC
• Datum reference: A (primary) / B (secondary, MMC if applicable) / C (tertiary, MMC if applicable)
• Representation: Hole and line vector in the 3D MBD model, identified as C/H

Pilot Hole (P/H):

• Drill hole diameter: .100" ±.008"
• Positional tolerance: .055" diameter at MMC
• Datum reference: A (primary) / B (secondary, MMC if applicable) / C (tertiary, MMC if applicable)
• Representation: Line vector only in the 3D MBD model, identified as P/H

The size tolerance on C/H is half that of P/H (.004 vs .008). And the positional tolerance on C/H is more than five times tighter (.010 vs .055). This is a massive difference in manufacturing cost and inspection requirements.

What This Means for Your Shop

For Coordination Holes (C/H):

Drilling: Standard twist drilling will not hold ±.004" on diameter consistently. Plan for precision reaming or boring as a finishing operation after the initial drill.

Positional accuracy: A .010" diameter positional tolerance at MMC is tight. On a 3-axis mill, this requires careful datum setup, probe verification, and potentially a dedicated boring cycle rather than a canned drill cycle. Temperature variation, tool deflection, and fixture compliance all become factors.

Inspection: CMM verification is essentially mandatory. You need to measure both the hole diameter (to verify the .100 ±.004 size) and the true position relative to datums A, B, and C. The positional tolerance is a diameter zone at MMC, meaning the allowable position error increases as the hole gets larger (bonus tolerance), but at the minimum material condition (.096"), the position must be within .010" of true position.

Tooling: Have calibrated pin gauges for the .096/.104 limits and bore gauges or air gauges for verification.

For Pilot Holes (P/H):

Drilling: Standard drilling is acceptable. The ±.008" diameter tolerance (.092 to .108) is achievable with a standard reamer or even a quality twist drill in a rigid setup.

Positional accuracy: The .055" diameter positional zone is generous by aerospace standards. A properly programmed CNC mill with a probed datum setup will hold this comfortably.

Inspection: CMM is still recommended for first article, but in-process verification with a go/no-go positional gauge may suffice for production runs.

How to Identify C/H and P/H on the Drawing

On a Boeing Product Verification Standard (PVS) or detail drawing, classified holes are identified in several ways:

In the general tolerance block: Look for notes labeled 10F (or similar) for C/H and 11F for P/H. These notes define the diameter, tolerance, positional requirement, and datum reference for each hole type.

In the drawing views: Holes will be annotated with "C/H" or "P/H" next to the hole callout, along with the quantity (e.g., "C/H 2 PLCS" or "P/H 3 PLCS").

In the 3D MBD model: C/H holes are represented as both a hole and a line vector. P/H holes are represented as a line vector only (no hole geometry). This distinction matters if you are working from the CATIA model rather than the 2D PVS.

Count Your Holes Carefully

On a real Boeing structural fitting we analyzed, the drawing showed C/H holes in the Left view (2 PLCS), Section view A-A (2 PLCS), and Front view (2 PLCS). P/H holes appeared in Section view A-A (3 PLCS) and the Front view (3 PLCS).

The critical question: are the holes shown in different views the same holes seen from different angles, or different holes? On a complex 3D part, a single hole may appear in two or three views. The Section view A-A and the Front view may both show the same C/H holes from different perspectives.

Getting the hole count wrong affects your quote. Each C/H requires precision reaming and CMM verification, which takes roughly 3-5x longer per hole than a standard P/H. If you quote 2 coordination holes but the part actually has 4, you have underpriced the job.

The safest approach: count unique hole positions from the 3D model if available. If working from 2D views only, cross-reference the views to identify which holes are the same feature seen from different angles.

The MBD Complication

Many Boeing drawings are now Product Verification Standards (PVS) where the 3D MBD CATIA model is the design authority, not the 2D drawing. The 2D PVS may be intentionally incomplete, showing only the information needed for verification rather than full manufacturing detail.

For classified holes, this means the 3D model contains the definitive hole positions, while the 2D drawing shows the classification (C/H or P/H), tolerances, and inspection requirements. You need both to manufacture the part correctly.

If you receive only the 2D PVS without the 3D model, your first clarification question to the customer should be: "Please provide the 3D CATIA/STEP model, or confirm that all manufacturing data is contained in the 2D drawing."

FAI Implications

In the AS9102 Form 3 for a part with classified holes, each hole type generates multiple FAI characteristics:

For each C/H:

• Hole diameter: .100 ±.004, measured with bore gauge or air gauge
• Positional tolerance: .010 dia at MMC, measured with CMM relative to datums A/B/C

For each P/H:

• Hole diameter: .100 ±.008, measured with bore gauge or standard gauge
• Positional tolerance: .055 dia at MMC, measured with CMM relative to datums A/B/C

The C/H positional tolerance should be classified as "Critical" or "Major" in the FAI designator column. The P/H positional tolerance can typically be classified as "Major."

Mavlon Identifies Classified Holes Automatically

Mavlon's drawing intelligence reads the general tolerance notes, identifies C/H and P/H classifications, extracts the diameter tolerances and positional requirements for each type, and maps them to the correct FAI characteristics with appropriate designators and inspection methods.

When the drawing shows "C/H 2 PLCS" in a view, Mavlon captures the hole classification, links it back to the general tolerance note for the full tolerance definition, and flags it in the feasibility analysis with a warning: "Coordination Holes detected.

Require precision reaming and positional accuracy per Boeing specs.

Test it on your hardest drawing. Not a sample. Yours.