However there are certain circumstances where a crew of 2 may be required even on a single pilot ac. The most common of course is flight instruction where the instructor logs it as P1 and the student logs it as PUT (P2).
Well, which is it? PUT or P2?
There are however other circumstances where a crew of 2 may be required on a single pilot ac. For example, if you are making an instrument approach with an RVR less than 800m in a single pilot ac without a 2 axis autopilot with localiser capture then a crew of 2 is required.
Let's have the reference.