I first landed on the IPC roof in London in January 1975 in a Bo105D - can't remember any formal Cat A being in force for that type at that time. In fact in wasn't until four years later in June 1979 that I flew some rooftop take off single engine failure assessment flights on a 105DB with George Locke (ex-CO D Squadron at Boscombe Down) who was MD of Helicopter Marketing, the MBB sales agents in the UK at that time.