He would get all the security needed whether he flies commercial or special chartered plane. The only thing where I may go along with him travelling by charter is that of the inconvenience to others on the commercial flight. However unless he pays for the chartered plane I will go with the inconvenience for others.
Just curious, how is the PM reached in an emergency if he's flying commercial? Is it on an unsecured phone? What privacy/security is he guaranteed if he needs to talk with say...the POTUS?