The schwa is spelled <er> or <or> in this list. The /eə/ diphthong is spelled <air>, <are>, and <ère> in the loan word première.
This is a contrast between a short vowel which is always unstressed and a diphthong. It is not a problem for learners.
coarser corsair cos cares courser coursair coursers corsairs hector hectare hectors hectares premier première premiers premières