"The important thing in a congested airspace is spatial separation. Something went wrong with the spatial separation," says Jim Patterson, Former CA Assemblymember and Pilot.
Former State Assemblymember Jim Patterson is an experienced pilot who served for a decade as chairman of the California Legislative Aviation Caucus.
DC PLANE CRASH: A timeline of the deadly collision
In the flight's final moments, air traffic control asked the pilot to shift its landing route from one runway to another. Patterson thinks that could have contributed to the disaster.
"When the air traffic control said, can you land on this other runway you'll notice that the flight of the regional jet actually started to turn into the flight path of the helicopter," says Patterson.
The map below shows the flight paths of both of the aircraft. The American Eagle C-R-J regional aircraft banked left to land on Runway 33. The Army helicopter flying under the callsign 'PAT25' asked to cross the flight path.
Audio from air traffic controls captured the following: ''PAT25, do you have the CRJ in sight? PAT25 has aircraft in sight, visual separation."
The air traffic controller then tells the helicopter pilot to "pass behind" the American Airlines jet. But the two aircraft continue on the same path until they collide.
''Crash! Crash! Crash! this is an alert three! Crash! Crash! Crash!'' said a pilot prior to impact.
Dramatic video captures an explosion erupting in the sky, and wreckage falling from the air.
Since 2008, the NTSB has investigated 145 mid-air collisions in the US, but none have involved commercial flights.
DC PLANE CRASH VICTIMS: What we know about those on AA Flight 5342, Army Black Hawk
Aviation experts say more than one mistake may have led to the crash, including limited night visibility, the control tower's workload, and pilot error.
"If the helicopter was in the wrong altitude and we don't know yet that that's the case. But if they were, then obviously it had a bearing on the accident because it might have if they have been lower, missed the jetliner altogether," says John Nance, ABC News Aviation Analyst.
Fresno is home to one of only four Army Repair Depots for the Black Hawk helicopter involved in the crash, making them a common sight at our local airport, and in the skies above Central California.
The NTSB is now focused on ensuring a collision like this will never occur again.
"Our mission is to understand what happened but why it happened and to recommend changes to prevent it from happening again," says Todd Inman, National Transportation Safety Board Member.
Thursday, the two black boxes from the American jet are on their way to the NTSB lab. They will issue a preliminary report within 30 days. The final report will be released once all the evidence is carefully reviewed -- a process that typically takes a year or two.
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