>> thank you. cockpit doors on commercial jets and planes in the united states and security rules for them have changed dramatically since the a takes of 9/11 making it hijacking more difficult. the federal aviation administration says cook pit doors be tough enough to withstrand the blast from a grenade. before the attacks the doors were not reinforced and some pilots would leave them wide open, frankly, and invite passengers in to take a look at the controls. justin green is a commercially licensed pilot former marine pilot who works on crash investigations and is live. do you make wholesale changes based on the actions of one man. >> in 9/11, 19 men got into the cockpit in four different planes and take over the airlines, and those changes were made. these changes, the armored cockpit door were made in response to that going forward, this is an easy fiction to have two people in cockpits.