Huge disadvantage
Re: Cut the rubbish
An Airline with only one plane will always be at a huge disadvantage to carriers with 50 to 100 aircrafts.
It will never compete on a cost basis. Secondly passengers will always be loyal to only one thing. PRICE.
Lastly having only one plane is highly risky from the reliability point of view.
Just a single equipment failure like some kind instrument malfunction will render the 737 grounded for up to days at a time, ruining the schedule for all booked passengers, and costing S.A. a fortune.
John M.D.