The National Transportation Safety Board is investigating the fatal crashes of the American Airlines 737-800 and Boeing 737-700 jets, which were grounded after they took off from Atlanta to Fort Lauderdale in October 2001.
But the NTSB has been slow to act, and the planes involved in the incidents are still flying.
The two planes were the most fatal in airline history.
The NTSB said in a statement it is looking into the “tremendous” loss of human life during the crashes.
The agency also said that a “significant” number of its records have been lost in the fires, and it is working to restore them.
The American Airlines plane crashed in Minneapolis on Oct. 24, 2001, killing all 224 passengers and crew on board.
The Boeing 737 crashed on Sept. 25, 2002, in Fort Lauderdale.
The Air France Boeing 767 crashed in France on Sept, 12, 2003, killing 130 people and injuring nearly 3,000 others.
Both planes were grounded for months as investigators investigated the causes of the accidents.
Both crashes killed more than 100 people.
NTSB investigators have also found evidence that the airlines did not follow safe procedures in dealing with the aircraft’s fire, and that the airline had failed to properly assess the damage, the agency said in its statement.
The Federal Aviation Administration said in July that it will investigate the two crashes.