I suppose the next question is where do you get your equivalent of Rex Kramer from to do the talk down?...........
https://www.youtube.com/watch?v=U4tU3ZRFoUI
I guess if the aircraft is heading back to home base someone familiar with the aircraft might be available ...OTOH if the flight is heading off downroute then good luck.. "not one of ours" ....
Even at homebase, especially if in the U.K., can our author get our "Rex" through security and to the tower before the inbound aircraft runs out of fuel........maybe the author can arrange for the assisting pilot to be airborne in a company aircraft in the vicinity.....the plot could thicken...