How to Complete the UK CAA Form 1: Blocks, Status, and Signatures

Completing the UK CAA Form 1 correctly starts with picking the right blank template for your approval, filling the identification and item blocks the same way on either version, and then following the rules that split at Block 11: production organisations enter one of two statuses and sign Block 13, while maintenance organisations enter one of four statuses and sign Block 14. Whichever release block you don’t use has to be shaded so it cannot be signed by mistake. Get any of those wrong and the certificate is void.

Pick the Right Template First

The CAA publishes two distinct blank forms on its official forms page. “CAA Form 1–21” is the template for production releases under Part 21. “CAA Form 1 MO” is the template for maintenance organisation releases under Part 145.¹ The two templates share the same block layout, but the pre-printed text and applicable release statements differ, and the form reference printed on the document must match the type of release. Using the wrong template is one of the fastest ways to have a certificate rejected.

Production organisations use Form 1-21 when releasing a newly manufactured part, appliance, engine, or propeller into the supply chain. Complete aircraft are not released on a CAA Form 1.² Maintenance organisations use Form 1 MO to certify release to service after work on a component while it is off the aircraft, under 145.A.50.³ One narrow exception on the maintenance side: if an organisation maintains a component for its own use, an internal release procedure documented in the Maintenance Organisation Exposition can replace the formal certificate.

A note on scope. Since 1 January 2021, UK-based organisations holding a UK CAA Production Organisation Approval can no longer issue an EASA Form 1; any EASA Form 1 issued by a UK CAA POA holder after that date has no legal value.⁴ The UK CAA Form 1 replaced it for parts released under UK regulatory authority.

Blocks can be resized to fit your needs, but not to the point where the certificate becomes unrecognisable. Entries may be machine-printed, computer-generated, or handwritten in block letters, and abbreviations should be kept to a minimum.²

Blocks 1 Through 10: Identification and the Item

These blocks work the same way on both templates.

Block 1 identifies the approving competent authority and country. For UK organisations, this is the CAA and United Kingdom.⁵ Block 4 takes the full name and address of the issuing organisation as it appears on its CAA Form 55 Sheet A. Block 5 records the work order, contract, or invoice number so the certificate ties back to the specific job. Block 6 assigns a unique line-item number to each item on the certificate; every entry in the later blocks refers back to this number.

Block 7 is a plain-language description of the item. Block 8 records the part number exactly as it appears on the item or its tag and packaging. Block 9 states the quantity. Block 10 captures the serial number where regulation requires one.²

Block 11: What Status to Enter

This is where the two templates part ways, and it’s the block most commonly filled in incorrectly.

Production (Form 1-21)

Block 11 on a production certificate accepts only two entries:

NEW, for an item manufactured in conformity with approved design data.
PROTOTYPE, for an item manufactured against non-approved design data, such as a part built for testing ahead of type certification.

Maintenance-style terms like “Overhauled” or “Repaired” cannot be entered here on a production certificate.²

Maintenance (Form 1 MO)

Block 11 on a maintenance certificate accepts one of four entries, and only one. If more than one could apply, pick whichever best describes the majority of work performed:⁶

Overhauled: the item has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested to bring it into full conformity with the type certificate holder’s or manufacturer’s service tolerances.
Repaired: one or more defects have been rectified using an applicable standard.
Inspected/Tested: the item has been examined, measured, or functionally tested in accordance with an applicable standard, covering visual inspection, bench testing, and similar activities.
Modified: the item has been altered to conform to an applicable standard, such as a service bulletin or approved modification.

Block 12: Remarks

Block 12 is where the details behind Block 11 get written down, and its content depends on the template.

On a production certificate, a straightforward new-production item may need little in Block 12 beyond referencing relevant data. Certain situations demand specific entries: re-certification of a previously released item after alteration or rectification work, changes from prototype to new status once design data is approved, and corrections to a previously issued certificate all require explanatory statements here.² For manufacturing releases under Part 21 Subpart F, the Statement of Conformity required by 21.A.130 must be included directly in Block 12 rather than referenced in a separate document.⁵

On a maintenance certificate, Block 12 describes the work identified in Block 11 in enough detail, or by reference to supporting documentation, for the installer to determine whether the item is airworthy for its intended use. If the description runs long, a separate sheet can be attached and referenced from the main form. Each statement must clearly identify which line item in Block 6 it relates to.⁶

Block 13 or Block 14: The Release Statement

Only one of these blocks is signed on any given certificate. The other must be shaded, darkened, or otherwise marked so it cannot be used by mistake.

Block 13 for Production Releases

Block 13a is the production release statement. Tick one of two boxes: “approved design data and are in a condition for safe operation” for items built to approved data, or “non-approved design data specified in block 12” for prototype items, with the non-approved data identified in Block 12.² Block 13b takes the authorised signature. Blocks 14a through 14e are not used and must be shaded.

Block 14 for Maintenance Releases

Block 14a is the maintenance release statement. Mark the appropriate box indicating which regulation the completed work falls under. The phrase “unless otherwise specified in block 12” built into the certification statement covers three situations: where the maintenance could not be completed, where it deviated from the Part 145 standard, or where it was carried out under a different national regulation, which must then be specified in Block 12.⁶ Block 14b takes the signature. Blocks 13a through 13e must be shaded.

One Certificate, One Type of Release

A single CAA Form 1 cannot mix production-released and maintenance-released items. It also cannot combine items certified against approved design data with items certified against non-approved data.² A batch containing a newly manufactured component and a repaired one needs two certificates. A batch of parts where some are built to approved data and others are prototypes needs two certificates.

The certificate also does not automatically authorise installation. It certifies the item’s condition and conformity, but the installer must independently confirm the part is acceptable under the airworthiness authority governing the receiving aircraft.²

Who Is Allowed to Sign

Only personnel specifically authorised under the rules and policies of the CAA may sign Blocks 13b or 14b.² For maintenance organisations, certifying staff must hold a valid licence or authorisation compliant with ICAO Annex I, and the organisation must evaluate that licence against UK Part 66 categories and apply any necessary limitations.⁷

Minimum experience thresholds are tied to the category of work:

Category A (line maintenance): 3 years of maintenance experience.
Category B1 or B2 (line maintenance or base maintenance support): 5 years of maintenance experience.
Category C (base maintenance): 8 years of maintenance experience.

All certifying staff must also have completed Human Factors training and UK Aviation Legislation training at the level specified in UK Part 66 Appendix I modules 9 and 10. On top of those baseline qualifications, staff need at least 6 months of relevant experience within the two years preceding the date their authorisation is issued.⁷ A signature from someone whose authorisation has lapsed or whose scope doesn’t cover the work performed will invalidate the certificate.

Using Electronic Signatures

Electronic signatures are permitted, but the system generating them must meet a specific set of security requirements documented in the organisation’s exposition and submitted to the CAA for approval. The system must guarantee secure access for each certifying staff member, ensure data integrity with evidence of authenticity through recording and backups, and be active only at the location where the part is being released. Blank forms cannot be signed electronically; the system must prevent it.⁸

The signature itself must be uniquely linked to the signatory, capable of identifying them, and created using means the signatory maintains under their sole control. When an electronically signed certificate is printed, it must carry a watermark-type statement reading “PRINTED FROM ELECTRONIC FILE,” and Block 13b or 14b must state “Electronic Signature on File.”⁸ For electronic exchange between organisations, the CAA recommends established industry methods such as ATA Spec 2000 Chapter 16.

Fixing a Mistake After Issue

If the recipient of a CAA Form 1 spots an error, they must notify the issuing organisation in writing. The originator can then issue a corrected certificate provided they can verify and fix the error. A corrected certificate gets a new tracking number, a new signature, and a new date. It is a fresh document, not an amendment.²

The issuing organisation does not need to re-inspect or re-verify the condition of the item. However, Block 12 of the new certificate must contain a specific statement: “This certificate corrects the error(s) in block(s) [identify which blocks] of the certificate [original tracking number] dated [original issuance date] and does not cover conformity/condition/release to service.” Both the original and the corrected certificate must be retained for the full retention period associated with the first certificate.²

1
UK Civil Aviation Authority. Forms
2
Civil Aviation Authority. Appendix I – CAA Form 1 Authorised Release Certificate
3
Civil Aviation Authority. 145.A.50 Certification of Maintenance
4
EASA. Brexit – On the Consequences of the UK Withdrawal From the EASA System
5
UK Civil Aviation Authority. AMC No 2 to 21.A.130(b) Statement of Conformity for Products, Parts, Appliances and Materials
6
Civil Aviation Authority. Appendix II – Authorised Release Certificate CAA Form 1
7
UK Civil Aviation Authority. Part 145 Appendix IV Certifying Staff and Support Staff Not Qualified to Part 66
8
UK Civil Aviation Authority. AMC No 1 to 21.A.163(c) Computer Generated Signature and Electronic Exchange of the CAA Form 1