Good point Marco, after all aren't we really just flying around a cameraman/person and a radio operator/ess?
http://www.caa.co.uk/docs/122/summar..._transport.pdf
Rather than give a cut/paste job, as I read it we are only public transport flights only because the observers are passengers.
Further reading on the definition of pax would raise the question that if you are carrying observers who are "authorised to supervise training and carry out tests", then thay would be classed as crew and therefore it would not be a public transport flight.
Solution, make each observer a line trainer.
