Authorities said Sunday that the pilot of a medical helicopter that crashed in Maryland had twice radioed for help in foggy weather.

Officials Update Crash | Photos Of Bunker, Lippy

Four of the five people on board were killed, including the pilot.

WBAL-TV in Baltimore reported that the head of the State Police on Sunday identified the dead as pilot Stephen Bunker, 59, flight paramedic Mickey Lippi, 34, emergency medical technician Tanya Mallard, 39, and accident victim Ashley Youngler, 18.

A second accident victim, an 18-year-old girl who survived the crash, is in critical condition at Prince George's County Hospital.

The helicopter was sent to the scene of a traffic accident about 11 p.m. Saturday and picked up the two victims and a rescue squad member to take to Prince George's Hospital Center, according to authorities.

The medical helicopter was carrying victims of a traffic accident when it crashed in a suburban Washington park. The sole survivor, one of the traffic accident victims, is in critical condition.

It was the deadliest medevac helicopter accident in Maryland since the State Police began flying those missions nearly 40 years ago, and the eighth fatal medical helicopter crash in the last 12 months nationwide.

The National EMS Pilots Association said crashes of medical aircraft have been increasing since the 1990s, in part because it's a booming business, fueled by the closing of emergency rooms and by the aging population.

The state-run program in Maryland does not charge for its services, and was known for its safety record. It has had just three other fatal helicopter crashes in four decades.

A recent state legislative audit revealed that about a third of the medevac helicopters were out of service for 51 days during the past fiscal year. The audit also faulted the police agency for failing to document maintenance needs and failing to comply with federal and manufacturer repair orders.

State police have defended the unit. The General Assembly's Office of Legislative Audits also noted that the operation has an "impeccable" safety record.

The National Transportation Safety Board and the Federal Aviation Administration are investigating.