Andy Hawkins schrieb:

What's I find strange is that the stated format of the mayday ralay
does not follow international conventions. I wonder who wrote it?

The introduction says it is based on ICAO Annex 10 Volume 2 (Communications
Procedures).

It is.

International Civil Aviation Organization
International Standards and Recommended Practices and Procedures for Air
Navigation Services

Annex 10
Aeronautical Telecommunications

Sixth Edition October 2001


5.2.1.5.8 The following words and phrases shall be used in
radiotelephony communications as appropriate and shall have the meaning
ascribed hereunder:

Phrase: I SAY AGAIN
Meaning: "I repeat for clarity or emphasis."