Status:	Final
Date:	17 JUN 1948
Time:	12:41
Type:	Douglas DC-6
Operator:	United Air Lines
Registration:	NC37506
C/n / msn:	42871/12
First flight:	1947
Total airframe hrs:	1245
Engines:	4 Pratt & Whitney R-2800
Crew:	Fatalities: 4 / Occupants: 4
Passengers:	Fatalities: 39 / Occupants: 39
Total:	Fatalities: 43 / Occupants: 43
Airplane damage:	Written off
Airplane fate:	Written off (damaged beyond repair)
Location:	5 km (3.1 mls) ENE of Mount Carmel, PA (United States of America)
Phase:	En route (ENR)
Nature:	Domestic Scheduled Passenger
Departure airport:	Chicago (unknown airport), IL, United States of America
Destination airport:	New York-La Guardia Airport, NY (LGA/KLGA), United States of America
Flightnumber:	624

Narrative:
The airplane, named "Mainliner Utah", arrived in Chicago at 09:52 en route from Los Angeles to New York. After a 52-minute turnaround, the DC-6 departed for New York. The airplane climbed en route to its planned altitude of 17,000 feet. At 12:23, and at 12:27 the crew made a routine acknowledgment of a clearance to descend en route to an altitude between 13,000 and 11,000 feet. A little later a fire warning led the crew to believe that a fire had erupted in the forward cargo hold. They then discharged at least one bank of the CO2 fire extinguisher bottles in the forward cargo hold. Because they did not follow the correct procedure, the cabin pressure relief valves were closed. This caused hazardous concentrations of the gas to enter into the cockpit. These concentrations reduced the pilots to a state of confused consciousness probably resulting in loss of consciousness. An emergency descent was initiated until it described a shallow left turn, heading towards constantly rising terrain. Five miles east of Shamokin the airplane, flying only 200 feet above the ground, entered a right climbing turn. As it passed to the north of Mt. Carmel, the climbing turning attitude increased sharply. The airplane then crashed in a power line clearing on wooded hillside at an elevation of 1,649 feet. The airplane struck a 66,000 volt transformer, severed power lines and burst into flames.
Investigation revealed that the fire warning in the cargo compartment had been false.

PROBABLE CAUSE: "The Board determines that the probable cause of this accident was the incapacitation of the crew by a concentration of CO2 gas in the cockpit."

Sources:
» CAB File No. 1-0075-48
Sample newspaper article from Newspaperarchive.com