that involves installing some new circuit breakers and relays as well as making some wiring changes. the work takes about an hour to an hour and a half for each plane. the faa did not require the airline to do this. united is voluntarily doing the maintenance. united says only domestic flights are affected but many affected passengers say united never told them what s going on. it s nerve-racking on the parents. i m a nervous wreck already with a daughter going to new zealand. and then, you know, the stuff with the plane. makes you wonder what s going on with the planes. if there was a problem, they should have had a backup plan. reporter: an airline spokesperson confirms united discovered this problem during routine maintenance checks tuesday afternoon. they say they expect to have all of the repairs completed by wednesday afternoon. at o hare airport in chicago, john garcia for abc news. u.s. and mexican officials are investigating a deadly attack on two american law enforcem