A larger aircraft should never be put into service .. .

A.until the (airport's) landing fees can be negotiated to a level equal to or less than the smaller aircraft weight.

B.in most cases because of the extremely high non-operating costs associated with the larger equipment.

C.until the average passenger load achieved on the existing aircraft exceeds the load required for the larger aircraft to break even on the route(s)concerned.

D.unless the payload-weight ratio equals the stage length-to-weight ratio.