Of all the elements that BigMike has mentioned above, Certification in Category A is the most important - this element provides confidence that he helicopter can operate, without limitation, over a hostile environment.
Certification in Category A is required for operations in Performance Classes 1 & 2 by JAR-OPS 3.
CERTIFICATION
Helicopters certificated in accordance with FAR/JAR 29 are said to be in the Transport Category; helicopters certificated in accordance with FAR/JAR 27 are said to be in the Normal Category. (The break between FAR/JAR 27 and FAR/JAR 29 is 7,000lbs or 3,175kg - a helicopter certificated in accordance with FAR/JAR 27 is limited to 9 passengers)
Note: the precise certification standard of any helicopter type is governed by the revision status at the time that the type certificate was first issued. As certification standards develop, they are improved but are not applied retrospectively. It is considered that for Category A, amendment 39 of FAR/JAR 29 is a benchmark revision.
FAR/JAR 29 Category A
Category A is a certification standard which, by redundancy or design assessment to reduce the probability of failure, provides assurance of continued flight. Engine isolation ensures that one engine failure is unlikely to lead to a second, and fire in an engine compartment can be detected, contained and/or extinguished. These provisions give a level of confidence that the helicopter can be operated for continuous periods over a hostile environment.
Category A also requires the provision of performance data so that One Engine Inoperative (OEI) obstacle clearance from take-off, through climb, cruise and landing can be calculated; this data includes: mass related take-off and landing procedures; heliport/helideck size limitations; distances and climb gradients (or rates of climb); and one-engine inoperative climb performance graphs. From these procedures and graphs an operator/pilot can establish a complete OEI flight trajectory.
Although the helicopter is highly manoeuvrable in the slow speed regimes and can take-off from extremely small sites, its relative inefficiency - with respect to fixed wing - in the climb and cruise means it has a limited performance envelope. This is sometimes manifested as a single-engine height limitation or a requirement for reduction in the take-off or landing masses to achieve obstacle clearance. However, the helicopter’s flexibility ensures that it does not need a runway and can take off from obstacle rich confined sites, and elevated platforms, with operational payloads.
FAR/JAR 27 Category A
Light twins certificated in accordance with FAR/JAR 27 may be certificated to Category A in compliance with Appendix C of FAR/JAR 27. Appendix C calls up a number of requirements from FAR/JAR 29, which provide a similar (but not equivalent) level of airworthiness and the provision of performance data. It should not be assumed that all light twins certificated in accordance with FAR/JAR 27 have been certificated to Category A (even if performance data is provided or available).
It is my understanding that the B429 should be the first helicopter that will be provided with data (distances) to enable (simple) compliance with Operations in Performance Class 2 - both onshore and offshore.
Jim