IOGP-690 §25C: why one offshore seat needs up to three people

Ask a helicopter MRO how many mechanics an offshore contract needs and the quick answer is "two — one for day shift, one for night." That answer has sunk more than one contract's margin. This guide explains the rotation arithmetic behind IOGP-690 §25C, the oil & gas industry's aviation standard, and shows how to price offshore manning before the customer audit does it for you.

01The three hard limits

• 12-hour duty cap. No mechanic may be on duty more than 12 hours in any 24-hour period. A delayed arrival at 17:55 cannot be finished "just another hour" by the day crew — you need a rested second shift or the aircraft waits.
• 10-hour rest rule. After any duty period, at least 10 consecutive hours off before the next. This makes split shifts and back-to-back doubles mathematically impossible.
• 7 days off per month. Every mechanic must receive at least 7 rest days each calendar month. This is the rule that makes rotations mandatory — you cannot park two people on a rig permanently and comply.

Together these mean: the rig needs coverage 24/7, 365 days a year, but each individual can only be on the rig for a fraction of the year. The gap between those two numbers is filled with additional people on the roster — and that is where the multipliers come from.

02The rotation multiplier, explained in one formula

"NCS" stands for the North Continental Shelf — the North Sea oil & gas region (UK and Norwegian sectors), where the 2-weeks-on / 4-weeks-off pattern became the industry norm. It is generous to the crew and brutal to the roster: each person covers only one-third of the year, so three people rotate through every single seat.

03Worked example: 24/7 coverage for two AW169s

A contract: two Leonardo AW169s on a North Sea platform, operator requires 24/7 maintenance coverage, crews on 2/4 NCS rotation.

Two people on the rig at any moment. Twelve on the payroll. The ten who are home on their off-weeks are still salaried, still current, still consuming training budget. If the bid was priced on "two mechanics offshore," the contract is losing money from the first rotation — or the roster is quietly non-compliant and waiting for the audit.

04The audit moment

Oil & gas customers (the IOGP member companies) audit contractors against 690. The manning question arrives in a predictable form: "Show us your roster, your duty records, and how the roster satisfies §25C." A two-person roster claiming 24/7 coverage fails on inspection — no rest pattern exists that makes it legal. The auditor doesn't need to find a violation; the arithmetic is the violation. At that point the correction is re-pricing the contract mid-term, or losing it. Hence the industry's expensive classroom.

05Build it before you bid it

• Decide coverage first: day-only, extended, or 24/7 (2×12h or 3×8h) — this sets seats.
• Apply the rotation multiplier for the contracted pattern — not the one you hope to negotiate later.
• Add leave, sickness and training on top (the 1.25 permanent factor already embeds this; offshore patterns assume it in the on/off cycle).
• Document the derivation. One page showing seats × multiplier × support functions is the difference between defending a price and apologising for it.