The faa has issued an emergency air worthiness directive for at least 600 boeing 737s. a recent emergency landing due to vibration in the tail has mechanics inspecting a mechanism that controls the tail flaps for damage. joining me now, retired american airlines pilot and flight instructor tom casey. tom, good morning to you. this is the most flown airliner in the country? what does this mean for folks, what's an air worthiness test? >> air worthiness directive is a directive issued by the faa for typically inspection of parts that have been discovered to have wear damage, let's say, or as you...