To point out differences CAA Vs FAA, the FAA Instrument rating is neither single or twin, it is an instrument rating for that category and class. With it you can fly on instruments in similar flying machines. Separately, you must meet currency requirements in the aircraft category and class (as in rotorcraft-helicopter) to fly with passengers (logged 6 hours actual or simulated instruments and 6 instrument approaches in the last 6 months). That means that an S-76 pilot must keep current, and he/she can fly any helicopter on instruments.
If you fly commercially (psrt 135 air taxi for example), you must meet the commercial standards - which require a type check on the aircraft that you fly for hire, that must be repeated each 6 months. The type check spot checks your instrument proficiency, as well as handling and emergencies. The check is typically given by your company check pilot (an FAA designee), often as part of a regular revenue trip. It can also be given in a sim.
[ 24 February 2002: Message edited by: Nick Lappos ]</p>