they were blowing up what appeared to be old hawaiian DC9 variants.

pressurized two planes to 16k feet. detonated C4 in the first and blew a huge hole in the side and roof. detonated the second with a blast coating installed (looked like huge white bubble wrap). another huge hole, however it was 30% smaller than the first.

in both instances an AC flying at 16K or higher would have broken into bits.