When an aircraft is covered in fabric — whether Grade A cotton, polyester, or an approved synthetic system — the raw edges of the fabric and the stitching that secures it to the airframe structure are among the most vulnerable points on the entire covering system. Left exposed, these edges can fray, lift in the airstream, and eventually allow moisture and UV radiation to undermine the entire covering. Pinked tape exists specifically to solve this problem. It is a woven fabric tape whose edges have been cut with a zigzag (pinking) blade, producing a serrated margin that resists unraveling and bonds to the doped surface more securely than a straight-cut edge. Understanding why pinked tape is used, how it is applied, and what the FAA-accepted overlap standards are is essential knowledge for any airframe technician — and a reliable subject on the AMT knowledge test.
This article covers pinked tape in the context of certified aircraft fabric covering per FAA Advisory Circular 43.13-1B (Acceptable Methods, Techniques, and Practices — Aircraft Inspection and Repair), which is the primary FAA reference for fabric covering work on certificated aircraft. All dimensional requirements and application methods described here are grounded in that document and in the principles found in the Aviation Maintenance Technician Handbook — Airframe (FAA-H-8083-31).
What Pinked Tape Is and How It Is Made
Pinked tape is a reinforcing tape woven from the same type of fiber as the base fabric covering — typically cotton or polyester — and finished with pinked (zigzag) edges on both sides. The pinking serves two purposes. First, it prevents the woven tape from unraveling along its length during handling and after dope application. Second, the irregular serrated edge dramatically increases the surface contact between the tape and the underlying doped fabric, improving adhesion compared to a straight-cut edge that can peel away cleanly under aerodynamic flutter or vibration. Pinked tape is available in several widths, most commonly 2 inches, 3 inches, and 4 inches, and the technician selects the appropriate width based on the structural element being covered and the loading requirements at that location.
Where Pinked Tape Is Applied
Pinked tape is required at every location where the base fabric covering could be structurally compromised or aerodynamically lifted. The major application sites are:
- Fabric seams: Wherever two panels of covering fabric are joined — either by sewing or by overlapping — the seam must be covered with pinked tape to protect the joint and prevent the edge from peeling away in the airstream.
- Rib lacing (rib stitching): After rib cord is applied to stitch the fabric to the wing ribs, a strip of pinked tape is applied directly over the rib, covering the stitching and all knots. This tape protects the cord from abrasion and UV degradation and prevents aerodynamic forces from lifting the stitching loop.
- Fabric edges at wing tips, trailing edges, and leading edges: Wherever the raw fabric terminates at a structural member, pinked finishing tape secures and seals the edge.
- Inspection openings and drain grommets: The reinforcing patches around these features are finished with pinked tape to protect their perimeters.
- Overlap seams on fuselage and control surfaces: Any place where fabric wraps around a structure and overlaps itself must be taped.
Overlap Requirements — The Critical Numbers
The most heavily tested aspect of pinked tape application is the minimum overlap — the distance that one layer of tape or fabric must extend beyond the feature it is covering or the edge it is bridging. The FAA establishes these minimums in AC 43.13-1B, and the technician must know them precisely because an insufficient overlap is a workmanship defect that can cause the tape to peel, the seam to open, or the rib lacing to become exposed in flight.
Tape Over Rib Stitching
When pinked tape is applied over a rib lacing strip, the tape must be centered over the rib and must extend beyond the rib on each side sufficiently to cover all stitching knots and the cord itself. The standard requirement is that the tape overlap each side of the rib cap strip by a minimum amount established in AC 43.13-1B. In practice, the tape must extend far enough that the pinked edges contact only fully doped, cured fabric — not a raw edge or another tape edge — ensuring a secure adhesive bond on each side.
Fabric Seam Tape Overlap
When pinked tape is applied over a sewn or overlapping fabric seam, it must extend at least 1 inch beyond the edge of the seam or reinforcing fabric it covers under standard conditions, per AC 43.13-1B. This means the total width of tape coverage across the seam is the seam width plus at least 1 inch on both the left and right margins. Because of this requirement, a wider seam calls for a wider tape. The technician must verify that the selected tape width will provide the required margin after the tape is centered over the seam, and always confirm the specific dimension against the applicable AC 43.13-1B table or approved data for the covering system in use.
Overlap at Structural Members
At leading edges, trailing edges, and wing tips where the fabric is folded over a spar or structural tube, the fabric overlap (not the tape itself) must meet the minimums specified in the applicable Supplemental Type Certificate (STC) data sheet for approved synthetic systems, or the minimums in AC 43.13-1B for Grade A cotton work. For overlapping fabric panels (where one panel overlaps another instead of a sewn seam), the overlap of the fabric itself must be at least 1 inch in areas of low loading, with greater overlaps required on high-stress surfaces. The pinked tape applied over such an overlap must again extend at least 1 inch beyond the overlap edge on each side.
Tape Application Sequence and Doping
Correct overlap is meaningless if the tape is not properly bonded. The approved method requires the technician to first apply a brush coat of dope to the fabric surface in the area where the tape will be placed. The tape is then laid into the wet dope, smoothed from the center outward to prevent bubbles and wrinkles, and then brush-coated with additional dope on top. This dope-tape-dope sandwich ensures the tape is fully impregnated and becomes an integral part of the covering surface rather than simply sitting on top of it. After curing, additional coats of dope and finish are applied over the entire surface.
Why Overlap Requirements Matter for Safety
The aerodynamic environment on a fabric-covered surface is surprisingly harsh. At cruise speeds, dynamic pressure creates a constant suction effect that tries to lift any edge that is not firmly bonded. A pinked tape that has too small an overlap on one side may begin to peel from its edge, creating a flutter that propagates along the tape length, eventually lifting the tape entirely. Once tape lifts, the rib stitching or seam beneath is exposed to the airstream, and the structural integrity of the covering system degrades rapidly. In extreme cases, fabric can separate from the wing structure, causing catastrophic control surface failure. The overlap minimums in AC 43.13-1B represent the FAA's engineering determination of the minimum bond area needed to prevent this failure mode under normal and maneuvering loads.
Key Numbers and Rules
- Minimum tape overlap beyond a seam: 1 inch on each side beyond the edge of the seam or feature it covers, per AC 43.13-1B.
- Minimum fabric panel overlap (overlapping joints, not sewn): At least 1 inch in low-stress areas; more in high-load areas per AC 43.13-1B or the applicable STC data.
- Common tape widths: 2-inch, 3-inch, and 4-inch; width selection must provide the required overlap margins after centering over the feature.
- Application method: Dope-tape-dope (wet bed, then top coat) to fully impregnate the tape.
- Governing reference: AC 43.13-1B, Chapter 2 (Fabric Covering); FAA-H-8083-31 Airframe Handbook, Chapter 3.
- STC systems: Polyester fabric systems approved under an STC (e.g., Poly-Fiber, Ceconite) may have manufacturer-specified requirements that differ from or supplement AC 43.13-1B — always consult the approved data.
Common Test Traps
- Confusing overlap sides: The 1-inch minimum overlap applies to EACH side of the seam or feature, not the total tape width. Students sometimes misread the rule as applying to the total tape width and select the wrong tape width on exam questions.
- Assuming all tape is the same: Pinked tape and straight-cut tape are not interchangeable in approved applications. The exam may offer straight-cut tape as a distractor; only pinked tape is acceptable for the applications described in AC 43.13-1B.
- Ignoring STC data for synthetic systems: If a question specifies a Poly-Fiber or similar approved synthetic covering, the answer must reference the manufacturer's STC data sheet, which can differ from the AC 43.13-1B Grade A cotton standards.
- Skipping the dope bed: A question may ask about the correct application sequence. Laying tape on un-doped fabric (dry application) is not approved — the dope bed is required for proper adhesion.
- Rib tape width selection: The tape must be wide enough to extend beyond both edges of the rib cap strip AND provide the required margin. Selecting a tape that only just covers the rib cap with no margin is a common mistake in practical and written test scenarios.