Little-known aspect of Britannia flight numbers: many thought they were random but until you listed out the flights by day of week, the pattern didn't become obvious. BY1 / 8 / 15 / 22 / 29 and so on were Monday numbers, BY 2 / 9 / 16 / 23 / 30 Tuesday and on it went. 198 would therefore be a Tuesday number and indeed 22 October 1996 was a Tuesday (and a "Reus day", back in the era). Useless piece of trivia, but there you go.
ha ha. I worked that out as well! Remember flying on BY047 NCL-IBZ on a Friday in 87 and BY014 on a Sunday NCL-TFS in 95!
always wondered is there was any other indicators in the number but didn’t appear to be base or destination or aircraft type dependent! .