BOS has a real shortage of gate space and parking stands, so when Icelandair adds a weekend flight from BOS
, they have to ferry the aircraft (B757) up to MHT
and park it there for the week.
I know DL
does maintenance on it during the week, so you can try and pull some strings and hop on it for the ride down to BOS
early Saturday mornings. I've never tried it, but it could be done.