having a daughter go to new zealand and then the stuff with the plane, makes you wonder what s going on with the planes. reporter: united insists it is not technically grounding its 757s, but it will cycle every single one of the jets through a maintenance check to ensure these key computer changes were done correctly. what does all this mean for passengers? well, if you re booked on one of these united 757s there s a good chance your flight will be delayed and possibly even canceled. it is an inconvenience in that my husband will be waiting for us, because he s already down there for work. and i m not sure how we re going to get there now. reporter: the checks take up to an hour and a half for every aircraft. lisa stark, abc news, washington. u.s. and mexican investigators say there is no motive yet for a deadly attack on two american law enforcement agents. they were driving along a highway in northern mexico when they were stopped at a roadblock. that is when gunmen who may