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."
Loss of control
| Status: | Accident investigation report completed and information captured |
| Date: | Thursday 17 June 1948 |
| Time: | 12:41 |
| Type: |  Douglas DC-6 |
| Operator: | United Airlines |
| Registration: | NC37506 |
| 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 |
| Aircraft damage: | Destroyed |
| Aircraft fate: | Written off (damaged beyond repair) |
| Location: | 5 km (3.1 mls) ENE of Mount Carmel, PA ( United States of America)
|
| Crash site elevation: | 503 m (1650 feet) amsl |
| Phase: | En route (ENR) |
| Nature: | Domestic Scheduled Passenger |
| Departure airport: | Chicago Municipal Airport, IL (MDW/KMDW), United States of America |
| New York-La Guardia Airport, NY (LGA/KLGA), United States of America | |
| Flightnumber: | UA624 |
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:
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:
 |
|
Classification:
Flightcrew incapacitationLoss of control
Sources:
» CAB File No. 1-0075-48Photos
Map
This map shows the airport of departure and the intended destination of the flight. The line between the airports does not display the exact flight path.
Distance from Chicago Municipal Airport, IL to New York-La Guardia Airport, NY as the crow flies is 1156 km (722 miles).
Accident location: Approximate; accuracy within a few kilometers.
Distance from Chicago Municipal Airport, IL to New York-La Guardia Airport, NY as the crow flies is 1156 km (722 miles).
Accident location: Approximate; accuracy within a few kilometers.
This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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Douglas DC-6
- 704 built
- 3rd loss
- 2nd fatal accident
- 2nd worst accident (at the time)
- 22nd worst accident (currently)
United States of America- 4th worst accident (at the time)
- 76th worst accident (currently)
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