United Airlines Flight 624

United Airlines Flight 624

A DC-6 similar to the aircraft involved in the accident
Accident summary
Date	June 17, 1948
Summary	In-flight fire (false warning) followed by crew incapacitation
Site	Conyngham Township, Columbia County, near Aristes, Pennsylvania
Passengers	39
Crew	4
Fatalities	43 (all)
Injuries (non-fatal)	0
Survivors	0
Aircraft type	Douglas DC-6
Aircraft name	Mainliner Utah
Operator	United Airlines
Registration	NC37506
Flight origin	Lindbergh Field, San Diego
1st stopover	Los Angeles Airport
Last stopover	Chicago Municipal Airport
Destination	LaGuardia Airport, New York City

United Airlines Flight 624, a Douglas DC-6 airliner, registration NC37506, was a scheduled passenger flight that originated in San Diego, California with stops in Los Angeles and Chicago en route to LaGuardia Airport in New York City. The four-engine propeller-driven airplane crashed at 1:41 p.m. Eastern Daylight Time on June 17, 1948 outside of Aristes, Pennsylvania, killing all 4 crew members and 39 passengers on board.

The Douglas DC-6 fleet had been grounded by Civil Aviation authorities for four months during the previous winter as a result of the fatal crash of United Airlines Flight 608 on October 24, 1947. It was determined that the crash had been caused by a design flaw that allowed vented fuel to be drawn into the heater air intake scoop that caused a fire in the cargo compartment. As a result, changes were made and a fire extinguisher system was installed on all DC-6 aircraft, including the accident aircraft.

Flight 624 from San Diego had just completed a routine initial descent as part of its approach into the New York area, when the forward cargo hold fire indicator light illuminated, leading the flight crew to believe there was a fire in that cargo hold. Although this later turned out to be a false alarm, the crew decided to discharge CO₂ bottles into the forward cargo hold, to try to extinguish the possible fire.

While proper operating procedure called for opening the cabin pressure relief valves prior to discharging the CO₂ bottles, to allow for venting of the CO₂ gas buildup in the cabin and cockpit, there was no evidence the crew opened the relief valves. Consequently, the released CO₂ gas seeped back into the cockpit from the front cargo hold and apparently partially incapacitated the flight crew. The crew then put the aircraft into an emergency descent, and as it descended lower it hit a high voltage power line, bursting into flames, then smashing through the trees of a wooded hillside.

Ed Darlington of radio station WCNR at nearby Bloomsburg said "there was no sign of life and apparently everyone was killed." The scene of the wreck was in a sparsely wooded area about five miles from Mt. Carmel, a small town 135 miles from Philadelphia where delegates are gathering for the Republican National Convention. News of the crash brought excited whispering from the delegates. No one knew for certain whether any high Republican officials were on the plane.