Quote from me:
"Sorry to challenge the consensus, but I'm fairly sure EAAC's long-haul flights (Super VC10s by then) used "East African" as the callsign. Knowing pilots, "East Aff" would be a tolerable abbreviation for short-haul flights (DC-9s, F27s) on VHF, but it would not come over with sufficient clarity on HF R/T. "
Since posting that, I've met a younger colleague who - although he never flew for EAAC - learned to fly at Nairobi-Wilson aerodrome in the 1970s. When I asked him what was EAAC's callsign, he unhesitatingly said "East Af".
That backs up the Comet memoir on Sothicpress, so either my recollection above is completely wrong, or the callsign used was different on HF.