just ahead on cnn they were buying medicine and they were caught in a confrontation. i would have told him don t go any further. more close calls on the ground and more runway incursions experts say are the result of an overloaded system. and it was just a big shake. they accuse the united states of plotting to create an asia pacific version of nato that could risk a repeat of a crisis breaking out in the region. live from london, this is cnn newsroom with max foster and bianca nobilo. it is tuesday, march 7, 9:00 a.m. in london, 3:00 a.m. in eastern texas. matamoros, mexico where investigators are working to track down four americans believed to have been kidnapped by a mexican cartels. and two families in south carolina have identified them. a relative contacted the fbi on sunday as soon as she found out the group is missing. they haven t spoken to their loved ones in days and are hoping for the best. felt a little uneasy because i told them i had a dr
reporter: in boston, a trifecta of trouble. federal authorities say a man attempted to open an exit door on united jet coming from elos angeles and allegedly tried to stab a flight attendant with a broken spoon before being tackled by other passengers. and on the ground two planes collided as one was being pushed back from its gate, all of that just a week after a lear jet almost litt edcollided with ano jet. there is a lot of runway alerting systems and they have a lot of advisory programs, but despite all of the efforts, runway incursions are increasing. statistics are headed wrong way and it is the most dangerous thing in aviation today. reporter: and still more trouble. last week a lufthansa plane carrying among others actor math