NOx Technical Code: Certification of Ammonia and Multi-Fuel Engines (MEPC 84)
Two distinct workstreams run on the NOx Technical Code: multiple engine operational profiles are already adopted and carry three firm dates, while certification of ammonia engines is still a draft awaited at MEPC 85. Conflating them makes it look as though nothing is in force.
Operational Explanation
The NOx Technical Code 2008, referenced by Regulation 13 of MARPOL Annex VI, sets out the test, survey and certification procedures (EIAPP – Engine International Air Pollution Prevention Certificate) for marine diesel engines subject to NOx limits. The Code, however, was historically designed for conventionally fuelled engines, leaving a procedural gap for new-generation engines fuelled by ammonia or in dual-fuel configuration on liquid fuels other than gas (methanol, ethanol).
These are two different workstreams. Multiple operational profiles have been adopted since 11 April 2025; ammonia is the only one of the two still in draft.
Workstream one: multiple operational profiles, already adopted
Resolution MEPC.397(83), adopted on 11 April 2025 at MEPC 83, amends the NOx Technical Code 2008 and is titled “Use of multiple engine operational profiles for a marine diesel engine, including clarifying engine test cycles”. Tacit acceptance on 1 September 2026, entry into force on 1 March 2027. Beware the two-date trap: 1 September 2026 is the acceptance date, not the entry into force.
Application is staged, and the criterion is the EIAPP certificate issue date: for a new individual or parent engine the amendments apply no later than 1 January 2028; for a new member engine added to a family whose parent was already certified before that date, no later than 1 January 2030. An engine that already holds its EIAPP stays outside, with two exceptions: if it undergoes a substantial modification on or after 1 January 2028, and if it is an identical replacement engine installed from that date and already equipped with multiple operational profiles, in which case the new chapter 8 of the Code applies.
The new rows in the Supplement to the IAPP Certificate do exist, but they do not come from the NOx Technical Code: they come from Annex VI. Resolution MEPC.408(84) amends Annex VI with the same subject and is in force from 1 September 2027. The circulated text adds three rows to section 2.2.1 of Appendix I, one per Tier: “NTC 8 (Multiple Engine Operational Profiles)”. The descriptor, the dates and the three Supplement rows are now read on the adopted text of the resolution, which adds to section 2.2.1 of Appendix I the entries 9f (Tier I), 10g (Tier II) and 11e (Tier III), each carrying the descriptor “NTC 8 (Multiple Engine Operational Profiles)”. Adopted 1 May 2026, deemed accepted 1 March 2027, in force 1 September 2027: the date this page already gave is confirmed. Still cited, for the record of the verification, the official IMO list of amendments of 3 July 2026; the three Supplement rows in Circular Letter No.5085 of 24 October 2025, which is the text circulated under article 16(2)(a) and not the adopted one. The PDF of the resolution did not open.
And a resolution entering into force in a matter of days
The page did not mention resolution MEPC.398(83) at all, adopted on the same 11 April 2025, which amends the NOx Technical Code on the “Certification of an engine subject to substantial modification or being certified to a Tier to which the engine was not certified at the time of its installation”. It enters into force on 1 September 2026. It rewrites chapter 7 of the Code and updates Appendix II with a new flow chart. The resolution moreover invites Parties to consider its early application. It is the provision with the nearest deadline on this whole page, and it was the one missing.
Workstream two: ammonia, and here the page was right
The procedural gap for non-carbon fuels exists and is not yet closed. The carbon balance method, by which the Code derives the exhaust gas mass flow rate, does not work on a fuel that contains no carbon. PPR 13 (9–13 February 2026) developed amendments to the NOx Technical Code introducing the hydrogen balance and oxygen balance methods, and MEPC 84 approved them — approved, not adopted. Adoption is expected at MEPC 85. Declared limit: on this point we did not open an IMO document. The content and the adoption session come from the session summaries of four Classification Societies and flag registries, concurring with one another; the expected entry-into-force date we found in no source and do not give.
So, today: EIAPP certification of an ammonia engine is not covered by amendments in force, and anyone ordering such an engine remains in the transitional phase this page describes. But saying that “the NOx Technical Code amendments” in general are not adopted has been false for sixteen months.
Regulatory Reference
NOx Technical Code 2008 (referenced by MARPOL Annex VI, Regulation 13); Adopted and dated: res. MEPC.397(83) of 11 April 2025, multiple engine operational profiles and test cycles, in force from 1 March 2027 with application from 1 January 2028 (1 January 2030 for member engines of already-certified families); res. MEPC.398(83) of the same day, certification of engines subject to substantial modification or recertified to a different Tier, in force from 1 September 2026; res. MEPC.408(84), amendments to Annex VI with the same subject as 397(83) plus three new rows in the Supplement to the IAPP Certificate, in force from 1 September 2027. Still in draft: the amendments to the Code introducing the hydrogen balance and oxygen balance methods for non-carbon fuels, developed at PPR 13 and approved — not adopted — at MEPC 84, with adoption expected at MEPC 85 (30 November–3 December 2026). The amendments to the EEDI/survey guidelines on the definition of primary fuel for non-gas dual-fuel engines (methanol, ethanol) also stand.
Scope of Application
Every Company that operates or plans to install ammonia-fuelled engines, or dual-fuel engines on liquid fuels other than gas (methanol, ethanol), subject to EIAPP certification under the NOx Technical Code.
Procedure / How to Complete It
- Separate the two deadlines. Already in force or dated: MEPC.398(83) from 1 September 2026, MEPC.397(83) from 1 March 2027, MEPC.408(84) from 1 September 2027. To be monitored: the amendments on non-carbon fuels, whose adoption is expected at MEPC 85 (30 November–3 December 2026).
- If an engine on board has been or will be subject to a substantial modification, or has to be recertified to a Tier other than the one at installation, apply the chapter 7 procedure as rewritten by MEPC.398(83): it is in force from 1 September 2026, and the resolution itself invited early application.
- For ships with ammonia-fuelled or non-gas dual-fuel engines already at the design or construction stage, coordinate with the engine builder and the Classification Society on the applicable EIAPP certification procedure during the transitional phase.
- For dual-fuel engines on liquid fuels (methanol/ethanol), verify the definition of primary fuel applied for EEDI calculation purposes, according to the updated guidelines.
- Prepare the engine's technical documentation so it can accommodate the new Supplement to the IAPP rows relating to multiple engine operating profiles, once the amendments enter into force.
- Do not assume that an ammonia-fuelled or non-gas dual-fuel engine is automatically excluded from NOx limits in the absence of a dedicated certification procedure: always check the applicable approach with the Classification Society in the meantime.
Practical Example
Example: an owner ordering a newbuild with an ammonia/diesel dual-fuel engine asks the engine builder and the Classification Society for a preliminary assessment of the applicable EIAPP certification procedure, monitoring in parallel the outcome of the formal adoption at MEPC 85 before the ship's delivery.
What Typically Goes Wrong
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| Treating “the NOx Technical Code amendments” as a single block still awaiting adoption, because the ammonia ones are | MEPC.398(83) drops out of view: in force from 1 September 2026, it covers every engine subject to substantial modification or recertified to a different Tier — that is, engines already on board, not just newbuildings | Keep two lists: the adopted resolutions with their dates (397(83), 398(83), 408(84)) and the drafts awaiting adoption (non-carbon fuels, MEPC 85) |
| Primary fuel definition for a methanol/diesel dual-fuel engine not verified against the updated EEDI guidelines | EEDI calculation potentially inconsistent with the current regulatory interpretation | Verify with the Classification Society the applicable primary fuel definition according to the most recent guidelines |
What the PSCO Checks
Operational Tips
- If you are evaluating an ammonia-fuelled or non-gas dual-fuel engine, don't wait for formal adoption at MEPC 85 to start the dialogue with the engine builder and Classification Society.
- Always distinguish between approved and adopted amendments, and do not extend the status of one to the other: on the NOx Technical Code, resolutions adopted in 2025 with firm dates coexist with drafts awaiting MEPC 85. The right question is not “has the Code been amended?” but “which amendment, and with what date”.
- For dual-fuel engines on liquid fuels, check the updated definition of primary fuel for EEDI calculation purposes, as it can affect the ship's energy classification.
Preparation checklist
Educational checklist. This summary supports learning and preparation only. It does not replace the vessel’s approved procedures, manuals, statutory documents, company SMS, or applicable official requirements. Completing it demonstrates neither compliance nor readiness for an inspection: it shows that a list has been read, not that the ship is in order. Always verify the current documents carried on board.
- MEPC.398(83) (substantial modification / recertification to a different Tier) considered for the engines on board: in force from 1 September 2026
- Dates of MEPC.397(83) (1 March 2027) and MEPC.408(84) (1 September 2027) entered in the regulatory calendar
- Drafts on non-carbon fuels monitored toward adoption at MEPC 85
- EIAPP certification procedure for ammonia-fuelled/dual-fuel engines coordinated with the engine builder and Classification Society
- Primary fuel definition for liquid dual-fuel engines verified for EEDI purposes
- Engine technical documentation prepared for the future multiple engine operating profiles
FAQ
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Last substantive revision of this page: 28 August 2026 · page fingerprint b4a6e561eb30