When a word contains a vowel plus an R, then the vowel is controlled by the R.  The vowel may be a static ER or a movement ER (ARE, AIR, OR, IRE, EAR).  This happens in these words:

Start:  S-T-ARE-T

Beer:  B-EAR

Fire:  F-IRE

Four:  F-OR

Care:  C-AIR

Fir:  F-ER

Hurt:  H-ER-T