Jimbo, Jezza et al (who's Al?)
In the FAA world the critical element is not the certificate (licence) held, but the operation. If the operation is Part 91, a 1st or 2nd class medical is appropriate if the pilot is gaining valuable consideration (doing it for dosh). If the pilot is flying for fun, then a class 3 is sufficient. The certificate (Private, Commercial or ATP) is irrelevant. To work for reward on a Part 91 op, the pilot MUST hold a Commercial or higher certificate, and a class 2 or higher medical.
In summary, a class 2 medical is fine for an ATP or Commercial holder on a Part 91 operation.
