Should you need to eject just say "I'm ejecting", don't bother with all that MAYDAY nonsense.
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I might say that to my GIB (if so equipped), otherwise, I'm pulling the "handles" and getting out. Let ATC figure it out. Of course, it is always best to transmit as much information to ATC (or whomever) prior to ejection ... if there's enough time.
By the way, I have no experience with ejection seat-equipped aircraft. I'm just a card-carrying coward, and as soon as the idea "eject" entered my brain, I'm outta there. I do, however, have a couple of friends who successfully ejected from stricken aircraft ... one from an F-105 at near M-1.
Cheers,
Grog