Understanding the Importance of Part-21 Approved External Technical Marking Kits
What Are External Technical Marking Kits?
External technical marking kits encompass decals, placards, and stencils that convey critical operational and maintenance information directly on the aircraft’s exterior. These markings serve functional, regulatory, and safety purposes, providing key identifiers and operational data for crews, ground staff, and maintenance personnel.
When Are They Needed?
External technical marking kits are typically required:
- When an aircraft undergoes repainting or livery changes.
- For compliance with modifications or repairs that necessitate changes in exterior markings.
- To meet regulatory requirements for maintenance or operational updates
- During new aircraft delivery, from the OEM or to a new region where a refresh of the external markings and additional translations may be required
External marking kits are not standardised in a single comprehensive document for straightforward replacement. For instance, while certain aircraft models like the A320 have a defined minimum set of EASA-required placards and markings outlined in Airbus document Ref PR1413152 iss4, this document explicitly states that it “…does not cover all customised aircraft definitions.” In reality, it addresses only a small fraction of the extensive external technical markings required on the A320. This highlights the complexity and variation involved in ensuring accurate and compliant external markings for each specific aircraft configuration.
In this article we do not discuss aircraft registration markings, which are a special type of external technical marking, as they follow well defined standards and regulations such as CAP 523 (UK), AC 45-2E (FAA) and other regional standards.
Decals vs. Placards: What’s the Difference?
- Decals: Made from durable, adhesive-backed materials, decals are designed for semi-permanent application. They can withstand exposure to the elements and are typically used for high-visibility markings like emergency exits or registration numbers.
- Placards: Often more rigid and thicker than decals, typically not designed for external use. Placards are more suited for structural components or areas requiring durability under mechanical stress, regular cleaning or passenger abuse.
Why Are These Markings Crucial?
External markings:
- Ensure Regulatory Compliance: They align with operational and safety standards, often referenced in aircraft maintenance manuals (AMMs) and illustrated parts catalogues (IPCs).
- Enhance Safety and Functionality: Clearly visible and accurate markings prevent operational errors and reduce risks during ground handling or maintenance.
- Support MSN-Specific Customisation: Correct markings accommodate MSN-specific configurations like unique engines, panel assemblies, or power plant details.
- Meet National Aviation Authorities or Regional Requirements: Certain regions will have specific local regulations and requirements, such as for dual-language emergency markings.
The Scale of External Technical Markings Kits
Marking kits comprise of placards, decals, stencils or a mix of all three for various areas of the aircraft’s external structure. They can cover:
- The general fuselage area
- Doors detailing normal and emergency use based on door type
- Wing placards
- General landing gear placards
- Fuselage service panel placards
- Stabilisers placards
- Landing gear tyre pressure placards
- Engine placards based on the engine type
- Engine panel numbers
- Power plant cowl assembly placards
To illustrate the complexity, let’s consider the Airbus A320 family of aircraft. Below are some numbers we collected based on a single project we carried out recently:
| Aircraft Model | Number of Placard Types | Total Quantity |
| A319 | 439 | 712 |
| A320 | 498 | 833 |
| A321 | 528 | 930 |
This are how some of those decals are listed in an IPC:
And what they look like in reality from a different part of the aircraft:
It’s a common misconception that placards are uniform across aircraft models or that there’s a universal set with only a few MSN (Manufacturer Serial Number)-specific differences. This isn’t the case. For example:
- Even within the “common” set for the same aircraft type, there can be up to a minimum of 25 differences between MSNs.
- MSN-specific categories, such as engine placards or landing gear tire pressure indicators, can result in a further 67 differences per MSN.
In other words, 92 different placards/decals between two MSNs of the same type, and the final quantity is even higher than this! A generic external marking kit with a Certificate of Conformance is clearly unable to accommodate these differences. End result – engineers and technicians running into trouble during maintenance or wasting valuable time during installation, potentially holding up aircraft release, or regulatory issues down the line.
The Role of a Part-21 DOA and POA
To produce and install accurate external technical markings:
- A Part-21 DOA (Design Organisation Approval) creates the design data which include installation locations, Part Numbers, Kit List and so forth by consulting the IPC, aircraft survey and liaising with the MRO or paint facility.
- This design data is passed to a Part-21 POA (Production Organisation Approval), which manufactures the kit and releases it with an EASA Form 1.
- The DOA provides Part-21 approval, detailed installation instructions and IPC supplements, ensuring seamless integration with the aircraft and supports continuing airworthiness as originally intended.
Common Pitfalls of using Generic Kits
- Generic Kits: Failing to account for MSN-specific differences often results in incomplete or incorrect marking kits. Missing or mismatched identifiers can lead to maintenance errors.
- Poor Colour Contrast: Markings must be legible against the aircraft livery; for instance, dark text on dark backgrounds compromises visibility, resulting in costly re-designs, re-prints and last-minute delays.
- Using low quality or non–standard materials: Failure to manufacture external technical markings to certain specifications will result in regulatory non-conformances and durability (e.g. peel-off, degradation to UV light)
- Increased workload for the MRO or paint shop: Getting the right balance of stencils to placards and decals can significantly reduce installation time. A generic kit does not account for this or the standard working practices of your MRO or paint shop.
Key Takeaway
If you’re repainting or modifying an aircraft, it’s critical to address the external technical markings. Partnering with a Part-21 DOA ensures you receive a fully customised and accurate marking kit, and having it manufactured at a Part-21 POA ensures it matches the DOA data and comes with regulatory approval and EASA or UK CAA Form 1 certification.
By investing in the right expertise, you protect your aircraft’s operational integrity, enhance safety, ensure regulatory compliance and keep your MRO partner working efficiently.
Interested in learning more about External Technical Marking kits or other Part-21 subjects? Let’s connect and discuss your requirements! Get in touch via info@knsi.co.uk or call us on +44 (0) 1279 297000.
