WASHINGTON, April 8 (Reuters) - The head of the Federal

Aviation Administration's air traffic organization is stepping

down after more than 35 years with the agency.

Tim Arel, who is chief operating officer of the FAA Air

Traffic Organization, has decided to take part in the USDOT's

voluntary deferred retirement program, sources told Reuters.

Questions have been raised about why the agency did not address

concerns about close calls between helicopters and airplanes

near Reagan Washington National Airport before a Jan. 29 fatal

collision between an American Airlines ( AAL ) regional jet and

Army helicopter killed 67.