NOx Technical Code: Recertification, Multiple Profiles and the Ammonia/Hydrogen Draft
NOx: modification and recertification, multiple profiles and phased application. For multi-fuel engines, distinguish the adopted requirements, the non-carbon fuels project and the EEDI track.
Operational Explanation
The NOx Technical Code governs testing, surveys and EIAPP certification of engines subject to regulation 13. Distinguish NOx modifications and profiles, the non-carbon fuels project and EEDI verification.
Substantial modifications and profiles can also concern conventional diesel engines, not only ammonia and dual-fuel engines.
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.
MEPC.397(83) enters into force on 1 March 2027; paragraph 4 distinguishes application by EIAPP date. A new individual engine or previously uncertified parent of an Engine Family or Engine Group: no later than 1 January 2028. A new member with its parent certified before 2028: demonstrate family/group compliance before member certification, no later than 1 January 2030. No blanket application to engines already holding an EIAPP: substantial modification from 2028 follows amended definition 1.3.2 and the EIAPP date; an identical replacement installed from 2028 uses the Code version linked to the original EIAPP, unless the replaced engine already had multiple profiles, in which case chapter 8 applies.
MEPC.408(84) enters into force on 1 September 2027, adding entries 9f, 10g and 11e to the IAPP Supplement. Its paragraph 4 refers to the application dates in MEPC.397(83), paragraph 4: no blanket renewal of every Supplement on 1 September 2027.
Modification and recertification: section 7.2 already in force
MEPC.398(83) has been in force since 1 September 2026. It retains former chapter 7 as section 7.1 and adds 7.2 for installed engines substantially modified or certified to a different Tier. The route admits an individual engine or Engine Group, not Engine Family. Agree the test plan with the Administration before scheduling the test (7.2.10). The nominal 100% load point may not fall below 85% of rated power under the plan; otherwise defer the test (7.2.5). Even at an accepted reduced load, retain the test cycle’s 100% point weighting factor in the calculation. Replace the nameplate if rated power or speed changes (7.2.4).
The NOx non-carbon fuels project and the separate EEDI track
The NOx project for non-carbon fuels, such as ammonia and hydrogen, is distinct from adopted instruments. The official MEPC 84 summary, consulted on 16 October 2026, reports approval of amendments for subsequent adoption: it does not present them as already adopted or in force. The full final text of the new methods is not documented here, so no requirements or commencement date are anticipated. Methanol and ethanol contain carbon and fall outside this specific project.
The third track is EEDI: MEPC.411(84), paragraphs 4.2.3–4.2.4 and footnote 3, addresses primary fuel, specific fuel consumption and documents, including liquid-fuel dual-fuel engines. The Administration makes the final primary-fuel decision; manufacturer and verifier supply and examine evidence. This is not a new NOx rule.
Regulatory Reference
Adopted references: MEPC.397(83) (paragraph 4, definition 1.3.2, chapter 8); MEPC.398(83) (7.2); MEPC.408(84) (paragraph 4 and Supplement); MEPC.411(84) (EEDI 4.2.3–4.2.4).
For MEPC.408(84), the adopted text in annex 4 to the MEPC 84 report is available. The IMO Knowledge Centre entry consulted on 16 October 2026 still states “awaiting certification”. The report confirms commencement, the application cross-reference and IAPP Supplement entries; text availability and the entry’s certification status remain distinct.
Scope of Application
Engines subject to regulation 13, including conventional engines, in relevant modification, recertification or profile cases. The non-carbon fuels project and EEDI verification have separate scopes; they do not apply indiscriminately to every EIAPP.
Procedure / How to Complete It
- Identify original engine, identical/non-identical replacement, addition, modification or new Tier. Check regulation 13.2 and the recognized organization's authorization.
- If section 7.2 applies, agree the test plan with the Administration before scheduling. Check individual-engine or Engine Group status, availability of the required load and the nameplate; retain the 85% minimum at the nominal highest point and the 100% weighting described above, or defer the test.
- Connect EIAPP date and engine history with the MEPC.397(83), paragraph 4 matrix set out above: new individual/parent, new member, substantial modification or identical replacement. For a replacement, also check the removed engine’s profiles before choosing the Code version.
- Where chapter 8 applies, identify each profile and its authorized conditions in the Technical File. Use it only within those conditions; record its identifier and evidence that its conditions were met, plus the date and time each change is completed. Multiple profiles do not mean multiple fuels or free choice of calibration.
- Check the link between the engines concerned and new IAPP Supplement entries 9f, 10g and 11e under MEPC.408(84), paragraph 4. Use the application dates referenced to 397 without scheduling blanket renewal on 1 September 2027.
- For the separate EEDI track, prepare the primary-fuel, specific-consumption and documentary evidence under MEPC.411(84), paragraphs 4.2.3–4.2.4 and footnote 3. Involve the manufacturer and verifier; the final primary-fuel decision remains with the Administration.
- For ammonia/hydrogen agree the route with the Administration and authorized organizations; the future project is not a NOx exemption.
Practical Example
A conventional diesel being recertified to a new Tier follows section 7.2: agree the plan before scheduling the test. If the highest point cannot reach at least 85%, defer the test. For methanol/diesel dual-fuel also assess the EEDI primary fuel, without equating it to the NOx non-carbon fuels project.
What Typically Goes Wrong
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| Using Engine Family instead of Engine Group under section 7.2 | Certification may be prepared using a procedure not permitted for a family | Check individual-engine or Group status represented by the parent and agree the plan with the Administration |
| Ignoring the removed engine’s profiles in an identical replacement | An inapplicable Code version or verification route may be selected | Establish the original EIAPP and replaced engine’s profiles and apply the 397 paragraph 4(c)(ii) branch |
| Applying 397/408 to every engine from entry into force alone | Blanket tests or renewals not provided by the matrix may be scheduled | Separate entry into force from EIAPP dates and application; connect each case with 397 paragraph 4 and the 408 cross-reference |
| Using a profile without its conditions or records | The operating configuration lacks support from authorized conditions and required evidence | Connect identifier, conditions and data in the Technical File; also record the completion date and time of a change under chapter 8 |
| Treating EEDI primary fuel as NOx classification | The energy-calculation choice may be confused with emissions certification | Assess 411 separately from NOx/EIAPP; gather evidence for the manufacturer/verifier and Administration decision |
What the PSCO Checks
Operational Tips
- Maintain an engine–certification–Code version–date matrix.
- Separate adoption, entry into force and application.
- Agree tests and documentation before committing the operational window.
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.
- Identify original engine, identical/non-identical replacement, addition, modification or new Tier. Check regulation 13.2 and the recognized organization's authorization.
- MEPC.398(83) has been in force since 1 September 2026. It retains former chapter 7 as section 7.1 and adds 7.2 for installed engines substantially modified or certified to a different Tier. The route admits an individual engine or Engine Group, not Engine Family. Agree the test plan with the Administration before scheduling the test (7.2.10). The nominal 100% load point may not fall below 85% of rated power under the plan; otherwise defer the test (7.2.5). Even at an accepted reduced load, retain the test cycle’s 100% point weighting factor in the calculation. Replace the nameplate if rated power or speed changes (7.2.4).
- MEPC.397(83) enters into force on 1 March 2027; paragraph 4 distinguishes application by EIAPP date. A new individual engine or previously uncertified parent of an Engine Family or Engine Group: no later than 1 January 2028. A new member with its parent certified before 2028: demonstrate family/group compliance before member certification, no later than 1 January 2030. No blanket application to engines already holding an EIAPP: substantial modification from 2028 follows amended definition 1.3.2 and the EIAPP date; an identical replacement installed from 2028 uses the Code version linked to the original EIAPP, unless the replaced engine already had multiple profiles, in which case chapter 8 applies.
- Where chapter 8 applies, identify each profile and its authorized conditions in the Technical File. Use it only within those conditions; record its identifier and evidence that its conditions were met, plus the date and time each change is completed. Multiple profiles do not mean multiple fuels or free choice of calibration.
- MEPC.408(84) enters into force on 1 September 2027, adding entries 9f, 10g and 11e to the IAPP Supplement. Its paragraph 4 refers to the application dates in MEPC.397(83), paragraph 4: no blanket renewal of every Supplement on 1 September 2027.
- The third track is EEDI: MEPC.411(84), paragraphs 4.2.3–4.2.4 and footnote 3, addresses primary fuel, specific fuel consumption and documents, including liquid-fuel dual-fuel engines. The Administration makes the final primary-fuel decision; manufacturer and verifier supply and examine evidence. This is not a new NOx rule.
- For ammonia/hydrogen agree the route with the Administration and authorized organizations; the future project is not a NOx exemption.
FAQ
Related Topics
Certified substantive revision: 16 October 2026 · page fingerprint 4d2d76e169ff