Originally Posted by
Sally4th
I would guess there is also an element of what sounds good over the radio. Cactus has two syllables and hard consonants so it is very clear.
Ah, we have a winner. The main reason to adopt a callsign different from the airline's name is that the name itself is too long, or too heavy with mushy-sounding vowels that get lost in radio transmission. Note that all alternate callsigns have clipped, hard consonants: Clipper, Critter, Cactus, Speedbird, Redwood. The airlines they denote would be less easy to pick out of static: BeeOhAyyCee.... Pannamerricun... Virginamerricuh... etc. (The Speedbird call predates the BOAC / BEA merger.)