My DH says “an ‘abitual,” “an ‘istoric” and the like, happen when the word beginning the “h” is accented on the second syllable. Therefore the first syllable tends to drops the aitch. Or it did in the past, and still does in some regional accents including in the British Isles and all their former colonies and satrapies.
Satrapies. Beat that!
Vilayet!
Your dh is correct about AN, but the H is also pronounced. “An historic landmark.”
Sadly, this and many other rules of speech are being changed as keypads become the main method of communication among so many illiterates. This H issue is very controversial. I think the major newspapers now use only “A” insread of AN, who knows what their point is!?