The Oxford English Dictionary entry for the prefix "arch-" (at least as of the on-CD-ROM revision, I don't know since) specifically calls out "archangel" as the sole exception to the general pronunciation in English.
The Oxford English Dictionary entry for the prefix "arch-" (at least as of the on-CD-ROM revision, I don't know since) specifically calls out "archangel" as the sole exception to the general pronunciation in English.