They must pronounce it S P A, not "spa". In which case, it's "an" because S sounds like "ess", which starts with a vowel-like sound, so you use "an". I also p

They must pronounce it S P A, not "spa". In which case, it's "an" because S sounds like "ess", which starts with a vowel-like sound, so you use "an". I also pronounce it S P A, so "an" seemed immediately correct to me.