Your examiner asks: "What are the NOx Tiers under Annex VI, and which applies to your vessel's engines?"

A. Annex VI sets three NOx emission tiers (I, II, III) by keel-laying date and engine rated speed, with Tier III applying the strictest limit and being mandatory specifically for vessels operating within designated NOx Emission Control Areas (broadly aligned with the North American and US Caribbean ECAs, with further areas added over time) — a vessel's actual applicable tier and any NOx ECA obligation is recorded on its EIAPP Certificate and NOx Technical File for each qualifying engine.

B. NOx Tiers apply uniformly worldwide with no ECA-specific element; Tier III applies to every vessel built after 2011 regardless of operating area.

C. NOx Tiers are determined solely by ship size (GT), with no reference to engine characteristics or keel-laying date.

D. There are only two NOx Tiers (I and II); Tier III does not exist under Annex VI.

A. An Emission Control Area (ECA) is a designated sea area (e.g. Baltic Sea, North Sea, North American coasts, Caribbean) with stricter SOx (and in some, NOx Tier III) limits than the global rule. The global sulphur cap is 0.50% m/m (since 1 January 2020, IMO 2020); inside a SOx ECA the limit is stricter, commonly cited at 0.10% m/m, requiring either low-sulphur fuel, approved equivalent means (e.g. an exhaust gas cleaning/scrubber system), or use of an alternative fuel meeting the limit.

B. ECAs apply only to NOx and have no relationship to fuel sulphur content at all.

C. The global sulphur cap and the ECA sulphur cap are numerically identical; ECAs only add extra reporting paperwork.

D. ECA status applies only to passenger vessels; cargo ships transiting the same waters are exempt from the ECA sulphur limit.

A. A documented changeover procedure must be followed before ECA entry, completed in good time so that all fuel oil systems are flushed of higher-sulphur fuel before entry; the date, time, position and fuel oil tank quantities at the time of changeover (both entry and exit) must be logged — this changeover log is a specific item PSC and class auditors check, and is also entered in/cross-referenced with the Oil Record Book.

B. Fuel changeover may be completed instantaneously at the ECA boundary with no advance flushing of fuel lines required.

C. Only the changeover into the ECA needs to be logged; the changeover back to higher-sulphur fuel on exit has no logging requirement.

D. Fuel changeover logging is a class society recommendation only, with no regulatory basis under Annex VI.