HP's 757's have constant MTC issues. Another one this morning in DCA. 7am to PHX has mel can only take 112 pax. 69 pax have to be removed. These AC have MTC all the time and rarely operate on schedule. Where did they come from? I thought US ac 600 ,The Gem of the Eastern Fleet was bad news,but it was nothing compared to these P'sOS. Delay is now up to 2 1/2 hours , but will probably go to 3 plus.