the cause of these frightening close calls. reporter: the close calls involve air traffic controllers on each end of the country. may 9th in houston, united flight 601 was departing from vancouver on runway 9 as united flight 437 was leaving from mexico city on runway 15. the controller apparently made a serious mistake. 601, thank you, heading 340. instead of telling the vancouver flight to turn left he told him to turn right into the path of the other plane. the controller then quickly realized his mistake. united 601, stop your climbing and stop your turn, united 601. reporter: the planes came 400 feet vertically, .8 miles laterally. seconds away from disaster. arriving united 737 flew right over the top of a departing express jet regional flight that had been cleared for takeoff on an intersecting runway. do you have him in sight? maintain visual. oh, yeah, he s real close.
separating just in time. aviation correspondent rene marsh has the latest. reporter: kate, it has happened again. two planes with passengers on board get too close in the skies. now this morning the faa is investigating. two more passenger planes get too close in the skies. pilot 601, thank you, turn right, right turn. reporter: on may 9, united flights 601 and 437 took off from bush enter continental airport in houston at roughly the same time. shortly after takeoff flight 601 is told to turn right, putting it in the path of the other plane. moments later, the controller seems to realize the mistake. 601, stop your turn right there, sir. united 601 stop your turn, stop your climb and stop your turn united 601. reporter: the two planes came within nearly a mile of each other laterally and 400 feet vertically. one aviation analyst says at takeoff speed they were seconds
that it was an air traffic controller new in this position that directed one of the planes to take a wrong turn. this evening, the faa is trying to figure out why it happened. an air traffic controller in training directs a united jetliner to turn putting it on a possible collision with another jet taking off from the airport. seconds later, according to the faa, the controller realizes his mistake. stop your turn. stop your climb and stop your turn united 601. reporter: the two flights less than a mile away. listen to stunned pilots second later. i had no idea what was going on in the tower but it was pretty gnarly looking. reporter: putting a spotlight on something that actually happens every day. in the skies over the pacific, at new york s jfk and newark. he s real close. reporter: the rules of
close in the skies and this morning we know the faa is now investigating. 601, a right turn. two more passenger planes get too close in the skies. on may 9th, united flight 601 and united 437 took off from bush intercontinental airport in houston at roughly the same time. shortly after takeoff, flight 601 is told to turn right putting it in the path of the other plane. moments later, the controller seems to realize the mistake. 601, stop the turn right there, sir. stop your turn. stop your climb. stop your turn 601. reporter: the two planes came within nearly a mile of each other. 300 passengers on both flights may not have been aware of the close call but the pilots were left with questions as to what went wrong. 601, you know what happened there? basically crossed directly