Why were all Constellations grounded in the summer of 1946?

On July 11, 1946, the Lockheed L-049 Constellation registered NC86513 and named "Star of Lisbon" was flying a training flight for Transcontinental and Western Air, as TWA was then known, near Reading, Pennsylvania. Electrical wiring in the baggage compartment arced and caught fire while the aircraft was airborne. The smoke and intensity of the flames made it impossible for the pilots to maintain control of the aircraft, which ultimately crashed. Of the six crew members on board, five died. Since it was a training flight, there were no passengers.

The accident is remembered above all for what came next: all Lockheed Constellations were grounded from July 12 to August 23, 1946. The condition for returning to service was installing fire-detection equipment in the cargo holds of all aircraft of that model. The investigation was carried out by the Civil Aeronautics Board, the US agency that investigated air accidents at the time, whose report is preserved in the Department of Transportation's archives.

The grounding came right in the middle of the type's commercial rollout. The Constellation was the first widely used airliner family with a pressurized cabin, able to fly well above most bad weather, and airlines were just adding it to their long-haul routes when the accident occurred. The fact that an electrical fault in an unmonitored area could turn into an uncontrollable fire forced a review of how the cargo holds were protected, and fire detection in those compartments became a requirement for continued flight.