Accident Douglas DC-6 NC37506, Thursday 17 June 1948
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Date:Thursday 17 June 1948
Time:12:41
Type:Silhouette image of generic DC6 model; specific model in this crash may look slightly different    
Douglas DC-6
Owner/operator:United Airlines
Registration: NC37506
MSN: 42871/12
Year of manufacture:1947
Total airframe hrs:1245 hours
Engine model:Pratt & Whitney R-2800
Fatalities:Fatalities: 43 / Occupants: 43
Other fatalities:0
Aircraft damage: Destroyed, written off
Category:Accident
Location:5 km ENE of Mount Carmel, PA -   United States of America
Phase: En route
Nature:Passenger - Scheduled
Departure airport:Chicago Municipal Airport, IL (MDW/KMDW)
Destination airport:New York-La Guardia Airport, NY (LGA/KLGA)
Investigating agency: CAB
Confidence Rating: Accident investigation report completed and information captured
Narrative:
United Air Lines flight 624 was a U.S. coast-to-coast service from Los Angeles, California to New York, New York with an en route stop at Chicago, Illinois.
The Douglas DC-6, named "Mainliner Utah", arrived in Chicago at 09:52 hours local time. After a 52-minute turnaround, the DC-6 departed for New York. The airplane climbed to its planned en route 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 CO2 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 the aircraft described a shallow left turn, heading towards constantly rising terrain. Five miles east of Shamokin, Pennsylvania, the airplane, flying only 200 feet above the ground, entered a right climbing turn. As it passed to the north of Mount 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."

Accident investigation:
cover
  
Investigating agency: CAB
Report number: File No. 1-0075-48
Status: Investigation completed
Duration: 1 year 1 month
Download report: Final report

Sources:

CAB File No. 1-0075-48

Statistics

  • 2nd worst accident in 1948
  • 22nd worst accident of this aircraft type
  • 2nd worst accident of this aircraft type at the time

Location

Revision history:

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