way 100 miles from the mountain. >> so now you begin to ask the question what could cause a decompression and problems. >> looking at the plane's maintenance history, investigators learned there was previous damage to the aft pressure bulk head, the structure in the back of the cabin that keeps the cabin pressurized. it was cracked seven years before the crash. when the plane's tail accidently dragged along the runway, in an incident known as a tail strike. >> a tile strike can occur in one of two phases of flight, either on take justify where the airplane is on the runway and beginning the initial climb or it can occur on landing where the airplane is in a tail low, nose high latitude. either way, it will create some damage. >> the repair of the cracked bulk head is problematic. the structure is so large, more than 15 feet across the airplane