Human errors likely caused the Maryland State Police helicopter crash in Prince George's County last year that killed four people, according to the National Transportation Safety Board.

A decision by the pilot to try and "duck under" the cloud ceiling and not adhere to standard procedures for flying in low visibility, was the probable cause for the crash, the NTSB said.

Pilot Stephen Bunker likely kept his eyes off of the instrument panel, which would have given him his descent rate and altitude information, because he was "preoccupied with looking for the ground" before the crash, the NTSB said.

An air traffic controller at the Potomac Consolidated Terminal Radar Approach Control in Warrenton, Va., failed to give Bunker, who died in the crash, current weather conditions, which led him to expect that the cloud ceiling was higher than it actually was, the report found.

The NTSB said other factors contributed to or could have prevented the crash, including a lack of recent training for the pilot and local air traffic controllers who were unresponsive and inattentive.

Board member Robert Sumwalt took the Maryland State Police's aviation unit to task for not having equipped the helicopter with a terrain warning system or having implemented a formal risk assessment for pilots to use in determining whether they should accept a mission -- practices Sumwalt said the board had been recommending for years.

"I think the taxpayers of Maryland should be disappointed as well as those people requesting service," Sumwalt said. "And I hope that this accident will serve as a wakeup call."

The helicopter crashed around midnight on Sept. 27, 2008, when it slammed into 80-foot trees in Walker Mill Regional Park, about 3.2 miles north of Andrews Air Force Base. The aircraft had picked up two teenagers who had been in a car wreck in Waldorf and was diverted to Andrews after bad weather kept it from landing at Prince George's County Hospital in Cheverly.

The NTSB found that the helicopter was properly maintained, and there was no indication of mechanical failure. The board also said that there was a disorganized and disjointed search effort for the helicopter after it crashed, and the helicopter would have been missing for several more hours if it weren't for the effort of two aviation unit employees.

The sole survivor of the crash, Jordan Wells, 19, said she was later told that she had about 20 minutes left to live when she was found by rescuers.