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