Civil Aviation Order 108.10 Instrument 2007

The order defines three core terms. Dye penetrant material means any material forming part of a dye penetrant system, including cleaners, emulsifiers, developers and the penetrant itself. Dye penetrant process means the complete inspection procedure that defines how a dye penetrant system is used. Dye penetrant system means any combination of dye penetrant materials used together to effect an inspection. These definitions are narrow: the order does not cover other non‑destructive testing methods (ultrasonic, eddy current, radiographic) and does not purport to regulate the chemical formulation of the materials beyond the approval pathways. The central classification is Appendix I, which divides dye penetrant systems into seven groups based on the type of penetrant and developer. Groups 1-3 are colour contrast (visible dye) systems using solvent‑removable, post‑emulsifiable or water‑washable penetrants. Groups 4-7 are fluorescent systems, including water‑washable, post‑emulsifiable and solvent‑removable variants. Group 6 is designated “high‑sensitivity, post‑emulsifiable fluorescent penetrant”. The note to paragraph 1.1 warns that the groupings, taken from US Mil‑I‑25135C, set only a minimum sensitivity; a system in a lower‑numbered group could have sensitivity exceeding its group’s minimum. This creates a potential trap for inspectors who assume Group 4 is always less sensitive than Group 6. The concept of “approved” systems is central: automatically approved systems are tied to external specifications that are dynamic (“latest issue”), so compliance requires tracking updates to Mil‑I‑25135 and D.T.D. 929, as well as RAAF and manufacturer approvals. The order also introduces the concept of “equal or greater sensitivity” (section 4.1), allowing substitution of a more sensitive process. That discretion sits with the operator, but it is not unbounded: the substituted process must still be an approved dye penetrant system.

The primary duty‑holders are approved maintenance organisations (AMOs) and licensed aircraft maintenance engineers (LAMEs) who perform or supervise non‑destructive testing of aircraft components. Aircraft owners and operators are indirectly affected because airworthiness release of a component after dye penetrant inspection depends on compliance with this order. Small maintenance shops, particularly those in regional areas with limited access to specialist suppliers, face higher relative compliance burdens: they must procure only from manufacturers who can demonstrate qualification against US or UK military specifications, or obtain Director approval for alternatives. The order also affects manufacturers who wish to have their proprietary dye penetrant systems accepted without individual CASA approval: those systems must be qualified against Mil‑I‑25135 or D.T.D. 929, or be separately approved by CASA (section 3.2). The RAAF Quality Control Branch’s approval stream also means that military maintenance providers are an additional gatekeeper. The order does not explicitly address training or certification of the personnel performing the inspection, leaving that to other CAOs or the CARs. However, by mandating precise technical steps (penetration time, wash water temperature range 10-45°C, drying temperatures, ultraviolet light intensity minimums), the order effectively requires staff to be competent in following these procedures, creating an implicit training cost. For engineers who sub‑contract testing, the order adds contractual complexity: the principal must verify that the sub‑contractor’s systems are approved and that materials are checked per Appendix III. The compliance burden is not trivial for a small operator with one or two aircraft types, as the order does not allow any class‑based exemptions and requires record‑keeping of material checks and ultraviolet lamp tests.

Duty to use only approved dye penetrant systems (section 3.1). The order lists four auto‑approval streams; any other system requires Director approval under section 3.2. A breach of this duty is a breach of the CARs, carrying potential enforcement action including suspension or revocation of approvals, and possible criminal penalties.

Right to seek Director approval for non‑listed systems (section 3.2). The applicant must demonstrate that the alternative system’s sensitivity and non‑corrosive properties are at least equal to an already‑approved system. This right is available, but the demonstration burden is on the applicant; there is no prescribed form or time limit for the Director’s decision, creating regulatory uncertainty.

Duty to perform periodic checks (Appendix III). Penetrant materials that may be subject to contamination must be checked periodically for deterioration. At a minimum, a functioning test of the overall process must be conducted using a sample with natural or artificially induced cracks, assessing contrast, clarity, absence of spurious indications and ease of removal. Ultraviolet lamps and filters must be tested at least once every three months for intensity, with a minimum threshold (1,350 lumens per square metre at 380 mm). There is no stated grace period for overdue checks.

Duty to follow Appendix II process when no alternative specified (section 4.2). If neither a CAO nor an approved maintenance document specifies a dye penetrant process, the process in Appendix II becomes mandatory. This includes surface preparation (prohibiting shot peening, sand blasting or other mechanical sealing before inspection), mandatory drying at 70-110°C for at least 5 minutes (or 40 minutes at 70°C), a minimum 20‑minute penetration time, and a mandatory 10‑minute or half‑penetration‑time wait before final inspection (whichever is greater).

Right to use a process of equal or greater sensitivity (section 4.1) when a specific process is already prescribed. This gives operators some flexibility to use more sensitive systems (e.g. swapping a Group 3 colour contrast for a Group 6 fluorescent) without further approval. However, the right does not extend to using a lower‑sensitivity process; it is a one‑way ratchet.

Duty to clean parts within four hours after developer application (Appendix II, paragraph 6), especially for magnesium alloys.

Duty to use compatible materials on repeat inspections (Appendix II, paragraphs 7.1 and 7.2). The same process and materials from the same manufacturer must be used unless compatibility is established. Fluorescent penetrants must not be used to repeat an inspection where a colour contrast penetrant was used first.

The instrument itself does not prescribe penalties; enforcement comes from the parent regulation, subregulation 38(1) of the CAR 1988, which makes compliance with a CAO a legal obligation. Breach of a CAO is an offence under the Civil Aviation Act 1988 and the CARs, carrying maximum penalties that vary depending on whether the breach is by an individual or a body corporate. Historically, strict liability offences under the CARs for failing to follow maintenance procedures have resulted in fines, and in serious cases, suspension or cancellation of an AMO’s certificate. The order’s highly prescriptive nature means that even minor deviations , using a developer at the wrong temperature, exceeding the four‑hour cleaning window, failing to record a three‑monthly ultraviolet lamp check , are technically breaches. In practice, CASA’s enforcement approach has been risk‑based, but the order provides no safe harbour for de minimis non‑compliance. The economic consequences of enforcement extend beyond fines: an AMO with a compliance issue may lose its approval, which destroys the business. For an individual engineer, breach could lead to suspension of licence, effectively ending employability. The order also creates liability exposure in civil litigation: if a component fails and dye penetrant inspection was performed in a manner that did not meet the CAO’s requirements, the AMO or engineer could face negligence claims, and the insurer may deny cover. The two‑year limitation period for regulatory offences under the Civil Aviation Act adds a temporal pressure, but the order itself is permanent in effect until amended or revoked.

This CAO sits within the hierarchy of the Civil Aviation Regulations 1988. It overrides any inconsistent operator‑developed procedures that have not been approved. It incorporates by reference four external documents: US Mil‑I‑25135 (latest issue), UK D.T.D. 929, RAAF Quality Control Branch standards, and manufacturer overhaul manuals or process specifications. These documents are dynamic , “latest issue” , so an operator must keep track of revisions to US and UK specifications. Failure to do so could result in using a system that was approved at the time of qualification but has since been superseded or withdrawn. The order does not create any inconsistency with the Work Health and Safety Act 2011 (Cth or state equivalents), but the handling of dye penetrant chemicals, developers and solvents (especially trichlorethylene, which is a hazardous substance) is governed separately by WHS regulations. The CAO’s requirement to use trichlorethylene vapour degreasing “where possible” (Appendix II, paragraph 1.3) may conflict with WHS obligations to eliminate or minimise use of carcinogenic substances; the operator must navigate that tension. There is also potential interaction with the Australian Dangerous Goods Code if penetrant materials are stored or transported. The order does not address data privacy, export controls or intellectual property in the system formulations. For imported aircraft components, the CAO’s acceptance of US and UK specifications means that foreign‑approved systems are automatically recognised, reducing trade friction. However, a manufacturer in, say, Brazil or Japan would need to either qualify against Mil‑I‑25135 or D.T.D. 929, or seek Director approval under section 3.2, which adds a compliance cost not faced by US or UK suppliers.

The instrument was made on 11 December 2007 by Bruce Byron, Director of Aviation Safety, and commenced on 12 December 2007. It repealed and substituted the prior CAO 108.10 in its entirety. The text provided does not contain any subsequent amending instruments. Given that over fifteen years have passed, it is likely that later CAOs or amendments have been made, but those are not in the source material. The instrument is self‑contained as a new order, not an amendment to a larger CAO. The making of this instrument under subregulation 38(1) of the CAR 1988 indicates that it has the same legal force as a regulation, but it can be amended or revoked more quickly by CASA without parliamentary amendment. The use of “latest issue” in the auto‑approval references means that the order’s approval scope automatically expands or contracts as those external specifications are updated. This is a form of indirect amendment: when Mil‑I‑25135 issues a new revision, systems qualified under the old revision may become non‑approved unless they are also qualified under the new revision. The order’s silence on transition periods creates uncertainty: an operator holding stock of penetrant materials qualified under a now‑superseded Mil‑I‑25135 revision could be unknowingly non‑compliant.

The source text mentions no court or tribunal cases. The instrument is highly technical and prescriptive, which reduces the likelihood of litigation over interpretation of its terms. Most disputes would arise in administrative review proceedings before the Administrative Appeals Tribunal (AAT) if CASA refuses to approve an alternative system under section 3.2, or if CASA issues an enforcement notice alleging non‑compliance. There is no reported AAT decision specifically on CAO 108.10 that is publicly available and noted in the source, but that does not mean enforcement actions have not occurred. In general aviation, operators sometimes challenge CASA’s interpretation of “approved maintenance document” or “equal sensitivity”, but such disputes are usually resolved without publication. The order’s incorporation by reference of US and UK military specifications could generate argument over what “latest issue” means at the time of inspection , for example, if a manufacturer has a current qualification but CASA later argues that a newer issue exists and the system is no longer approved. No such case is cited, but the risk of differing interpretations is real. The note to Appendix I paragraph 1.1 warns that a Group 4 system may be of Group 6 sensitivity, which could lead to disputes if an inspector uses a Group 4 system believing it is adequate, only to have a regulator argue that a Group 6 system was required under paragraph 2.2 for fatigue cracks. The source does not resolve that ambiguity; litigation would turn on evidence of the specific system’s sensitivity.

Mandatory penetration time is 20 minutes minimum (Appendix II, paragraph 2.3). Many operators may feel that a shorter time is sufficient for small parts; the order does not allow any reduction unless the penetrant manufacturer qualifies the system for a shorter time outside the 2-50°C range. The time starts only after the surface is completely covered; holding a part in a penetrant bath for less than 20 minutes is a breach.

Drying temperature is tightly bounded (Appendix II, paragraph 1.2). Parts must be heated to between 70°C and 110°C; the time at temperature is a minimum of 40 minutes at 70°C or 5 minutes at 110°C. Overheating beyond 110°C is not permitted, even if it would speed drying.

No kerosene or gasoline as cleaning solvents (Appendix II, paragraph 1.3). Only trichlorethylene vapour degreasing or volatile solvents are allowed. Kerosene and gasoline are expressly prohibited because they can leave residues in flaws.

Prohibition on mechanical cleaning that seals surface openings (Appendix II, paragraph 1.4). Shot peening, glass bead peening and sand blasting must be avoided immediately before inspection. If such treatments are unavoidable, they must be followed by hand sanding with a sharp, well‑lubricated “wet and dry” paper. This adds a step many shops might skip.

Post‑emulsifiable systems prohibited on surfaces with abrupt changes (Appendix I, paragraph 2.3). Parts with threads, splines, keyways or any abrupt concavity cannot be inspected with Groups 2, 5 or 6 systems, because excess penetrant of varying depth would be retained.

Liquid suspended developers banned on surfaces with abrupt changes (Appendix I, paragraph 2.4). Where threads, splines, keyways or other abrupt concavities exist, only dry developer powder with fluorescent penetrant is allowed.

Sulphur‑ and chlorine‑free penetrants mandatory for titanium and nickel alloys (Appendix I, paragraph 2.5). Using a standard penetrant on these alloys can cause embrittlement or corrosion; the order makes no exception for small parts.

Repeat inspection restrictions (Appendix II, paragraphs 7.1 and 7.2). If a first inspection is inconclusive, the same process and materials from the same manufacturer must be used. Switching from colour contrast to fluorescent is forbidden. The note says the restrictions do not apply to routine service inspections after an elapsed period in service, but this distinction is easily confused.

UV lamp intensity checks every three months (Appendix III, paragraph 2.1). The minimum is 1,350 lumens per square metre (1,020 μW/cm²) at 380 mm, measured with specified meters. Missing a quarterly test by even a day is a breach; there is no grace period.

Cleaning parts within four hours of developer application (Appendix II, paragraph 6). For magnesium alloys, final cleaning is even more urgent. After four hours, penetrant residues become more difficult to remove and can cause corrosion.

Emulsification time is critical and must be determined experimentally (Appendix II, paragraph 3.3). There is no standard time; the operator must run tests for each part at each temperature to find the minimum time for acceptable background. If an operator uses a fixed time across different parts, it will likely be wrong for some.

Compliance begins with a clear inventory of all dye penetrant systems used by the organisation. Each system must be cross‑referenced against the four approval streams in section 3.1. For systems qualified against US Mil‑I‑25135 or UK D.T.D. 929, the operator must maintain copies of the current issues of those specifications and evidence (e.g. manufacturer’s certificate of compliance) that the system is qualified. For systems approved by the RAAF Quality Control Branch, the operator needs written confirmation from the RAAF. For systems approved in a manufacturer’s overhaul manual or process specification, the operator must have a copy of the relevant document. If a system falls outside all four streams, the operator must submit an application to CASA under section 3.2, with test data demonstrating sensitivity and non‑corrosive properties at least equal to a listed system. The application should include a detailed comparison. CASA has no statutory time limit to respond, so operators should allow several months.

For process control, the operator should adopt Appendix II as the default process for all dye penetrant inspections unless a CAO or approved maintenance document specifies otherwise. This means writing a company procedure that mirrors Appendix II verbatim, including surface preparation, penetrant application, dwell times, washing parameters (including water temperature range 10-45°C, no detergents), emulsification (if applicable), drying temperature (do not exceed 110°C), developer application (matching Appendix I paragraph 2.4 for surface changes), inspection (ultraviolet intensity at least 970 lumens per square metre for fluorescent, white light at least 1,080 lumens for colour contrast), and final cleaning within four hours. The operator must also establish a calibration schedule for ultraviolet lamps: a quarterly test against the 1,350‑lumens‑per‑square‑metre minimum, with records kept for audit. Penetrant materials must be subject to a functioning test using a reference sample with known cracks, at intervals determined by usage and contamination risk. The minimum requirement is an overall process test assessing contrast, clarity, absence of spurious indications and ease of removal. Before each test, the reference sample must be thoroughly cleaned to remove residues from prior tests.

Training of personnel is critical. The order does not prescribe certification, but the operator must ensure that each inspector can correctly interpret sensitivity requirements (e.g. knowing when Group 6 is required under Appendix I paragraph 2.2 for fatigue cracks), can perform the emulsification time experiment, and understands the prohibition on mechanical cleaning. Record‑keeping should capture: system approval documentation, batch numbers of penetrant materials, date and result of each functioning test, date and result of each ultraviolet lamp test, and individual inspection records for each part. The operator also needs to monitor changes to US Mil‑I‑25135 and UK D.T.D. 929; subscribing to notification services from the issuing bodies is advisable. Finally, the operator should review any Work Health and Safety obligations that may conflict with trichlorethylene use, and seek alternative approved cleaning solvents if required. A compliance audit checklist should cover: approved systems list, material check records, lamp test records, training records, and evidence that Appendix II has been followed for any inspection not covered by a specific manual process. Non‑compliance exposes the operator to penalties under the CARs and potential civil liability. The cost of compliance is not trivial, but it is a necessary price for maintaining airworthiness certification in Australian civil aviation.