The Wall Street Journal reported that the National Transportation Safety Board (NTSB) is suspecting pilot error in the Atlas Air Flight 3591, which crashed on February 23 in Texas, killing all three on board.

Flight 3591, which crashed on February 23 in Texas, killing all three on board. The plane was carrying US Postal Service and Amazon cargo.

Several pilots told Business Insider that the pilot's actions that the NTSB reported happening were unusual.

Inspectors with the National Transportation Safety Board (NTSB) suspect that pilot error — not aircraft malfunctions — led to the deadly Atlas Air crash on February 23, The Wall Street Journal reported on Friday. All three people on board died in the crash.

The NTSB said on March 5 that the Boeing 767-300 cargo jet entered some turbulence shortly before the plane's crash landing. Then, the engines increased to maximum thrust, after which the airplane pitch turned slightly up. That "startled the cockpit crew," The Journal reported, citing several sources familiar with the details.

The crew then tried to push the nose of the plane down. At a 49-degree angle, this caused an unusually steep descent, The Journal reported.

The NTSB said the plane accelerated to 495 mph as it dropped. The crew pulled the plane up to a 20-degree angle. Ultimately, in the last 18 seconds of the plane's descent, the crew lost control of the plane, the NTSB said.

The plane then nosedived into a muddy bay some 30 miles southeast of Houston George Bush International Airport.

An NTSB spokesman told The Associated Press that the agency is still investigating why the plane underwent a sharp change in pitch.

Read more: Pilots likely lost control of the plane carrying Amazon cargo before the crash killed all 3 on board, according to an initial review of the cockpit recording

Pilots told Business Insider that the actions taken during the flight were "perplexing" and not akin to typical flight maneuvers.

"I can't imagine," a pilot and former aviation-safety officer in the US military told Business Insider. "It sounds so off to me — totally counter to my instincts and training. I'd kick the autopilot and auto throttles off pretty darn fast."

"Obviously, going 49 degrees nose down is beyond a radical move," Todd Curtis, a former Boeing safety engineer who runs AirSafe.com, told The Associated Press. "That's not something an airplane should be doing, especially at that altitude."

Robert Sumwalt, the NTSB's chairman, predicted it would take more than a year of work to determine the cause of the crash, Flying magazine reported.

"This seems to be very much a mystery," Sumwalt said, according to the magazine. "But the NTSB has 52 years of experience solving such mysteries, and I'm confident we will get to the bottom of this."

Atlas Air pilots Capt. Ricky Blakely and First Officer Conrad Jules Aska, as well as Mesa Airlines Capt. Sean Archuleta, who was riding in the jump seat, died in the crash.

"Our thoughts and prayers are with all those who have been affected," Bill Flynn, Atlas Air's CEO, said in a statement on February 24. "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. We would like to commend the efforts of all of the first responders. We sincerely appreciate their efforts and support in the investigation."