Divers searched for flight-data recorders in marshland to help unravel why an Atlas Air Boeing 767-300 freighter crashed in Trinity Bay near Anahuac, Texas, on Feb. 23, after a steep descent, killing three crew members.

Briefing reporters at the scene on Feb. 24,NTSB Chairman Robert Sumwalt said controllers advised the pilots of Atlas Air Flight 3591 “that there was light-to-heavy rain ahead and provided radar vectors around the weather” as the 767 approached Houston George Bush Intercontinental Airport (IAH) from the southeast. Controllers lost radar and radio contact with the freighter as it flew at 6,000 ft. and 242 kt.

Video the NTSB received from the Chambers County Jail, located 1.4 mi. from the crash area, showed the aircraft “descending in a steep, nose-down attitude,” Sumwalt said. “…By looking at the video, I saw no evidence of the aircraft trying to turn or pull up at the last moment.”

Minutes after contact was lost, the freighter crashed in the shallow waters of the bay—the northeast portion of Galveston Bay on the Texas Gulf coast. Sumwalt described a debris field of about 200 yards long-by-100 yards wide from the impact. The remains of both wings were located within the debris field; pieces of the landing gear were found northwest of the debris path.

Retrieving the aircraft’s “black box” cockpit voice and flight-data recorders (CVR/FDR) in what local authorities describe as muddy, shallow marshland is a high priority, said Sumwalt, who indicated that underwater locator beacons attached to the recorders had not been detected.

“How are we going to find the black boxes if the ‘pingers’ don’t work? The situation we may be facing here is those pingers may be embedded so much into mud that their effectiveness may be reduced,” he said.

The Texas Department of Public Safety Dive Team had responded to the scene among other rescue organizations. Another option for finding the recorders may be to dredge the crash site, Sumwalt said.

Chambers County Sheriff Brian Hawthorne said responders had recovered two bodies from the crash site.

Atlas Air, which operated the flight for Amazon Air, on Feb. 24 announced that three people on board the freighter were killed. The Airline Professional Association, Teamsters Local 1224, had said earlier that it represented crew members on the flight.

“Our thoughts and prayers are with all those who have been affected,” said Atlas Air CEO Bill Flynn, who traveled to the accident site. “This is a sad time for all of us. Our team continues to work closely with the NTSB, the FAA and local authorities on the ground in Houston.”

Flynn added: “We would like to commend the efforts of all of the first responders. We sincerely appreciate their efforts and support in the investigation.”

The FBI’s Houston field office is assisting the NTSB by taking witness statements and collecting evidence to help document the debris field, Sumwalt said. The FBI also has issued a public appeal for any information, videos or photos of the crash. 

Other parties to the investigation are Atlas Air, Boeing, the National Air Traffic Controllers Association, the Teamsters union and GE Aviation, manufacturer of the aircraft’s CF6-80C2 engines.

The incident marked the first fatal crash of a large cargo airliner in the U.S. since Aug. 14, 2013, when a UPS Airbus A300-600 crashed short of the runway at Birmingham-Shuttlesworth International Airport, in Alabama, killing two crew members.