The plane crashed into a mountain — and exposed one of the US's best-kept secrets

On December 1, 1974, a TWA Boeing 727 crashed on the slope of Mount Weather in Virginia, about 25 nautical miles from Dulles International Airport near Washington. All 85 passengers and seven crew members on Flight 514 were killed. However, the fatal disaster soon became an even bigger story: the crash site drew public and media attention to a secret government facility located in the mountain area — a site linked to the US government's emergency plans.

More than half a century after the disaster, the story of Flight 514 is back in the headlines following new publications in the United States that re-examine one of the most unusual aviation accidents in the country's history — not only because of the 92 fatalities and the changes it brought to flight safety, but also because of the place where the plane crashed: near the secret government facility at Mount Weather.

Flight 514 departed from Indianapolis, stopped in Columbus, Ohio, and was supposed to continue to Washington National Airport. However, the weather disrupted the plan. Difficult conditions in the capital area led to the plane being diverted to Dulles Airport, and the crew began preparing for a landing at a place that was not their original destination.

Conditions were far from ideal. The plane was flying inside clouds and in weather conditions that limited the crew's ability to see the ground. According to a later review by AOPA, wind gusts in the Dulles area reached about 40 knots. During the approach to Dulles, air traffic controllers instructed the plane to descend gradually. Finally, it reached an altitude of 7,000 feet. And then came the instruction that became the center of the disaster investigation.

The controller cleared the flight for the VOR/DME approach to runway 12 — but did not add a new altitude restriction to the instruction. The pilots understood from the clearance that they could start descending to an altitude of 1,800 feet, which was the altitude set for a later stage of the landing approach. After receiving the clearance, the captain said to the first officer: "1,800 is the bottom." The first officer replied: "Start descending." However, they were still very far from the airport.

The descent began when the plane was about 44 nautical miles from Dulles. According to the investigation, a minimum altitude of 3,400 feet was required in the area where the plane was located. The altitude of 1,800 feet was safe only after reaching a later part of the approach path. The crew did not realize that the plane was on a collision course with the mountain.

At approximately 11:09, the passenger plane hit the western slope of Mount Weather. All 92 people on board were killed. Then an unusual detail about the crash site was discovered: the tragedy occurred in a particularly sensitive area. In the vicinity of Mount Weather was a secret government facility, which was linked to plans designed to allow the federal government to continue operating during a national disaster, including nuclear war scenarios.

Already in reports published immediately after the crash, the fact that the plane crashed near a secret government base was mentioned. A student newspaper from Ohio, for example, published a report the day after the disaster stating that the plane crashed "near a secret government base." Thus, a fatal aviation accident also became an event that turned an unwanted spotlight on one of the US government's most sensitive sites.

The NTSB investigation focused on the question of how a functional passenger plane, which was under the control of an experienced crew, reached such a dangerous altitude. The conclusion was that it was not a mechanical failure that brought the plane down. The crew simply descended too early. But the investigators did not stop at assigning responsibility to the pilots. They found a broader problem: the pilots and air traffic controllers did not understand the meaning of the approach clearance in the same way.

The NTSB determined that the decision to descend to 1,800 feet was made before the plane reached the point where this altitude was safe, and that this was also due to a lack of clarity and deficiencies in air traffic control procedures. The approach chart used by the pilots also contributed to the confusion. According to the FAA, one part of it indicated a minimum altitude of 3,400 feet at the initial stage, while another presentation of the data could have created a different impression.

One of the most worrying details was discovered only during the investigation. In October 1974, about six weeks before the disaster, a United Airlines plane performed the same approach to Dulles — and its crew also understood the instructions in a similar way. The plane descended to 1,800 feet too early and almost got into a similar disaster, but managed to land safely. The incident was investigated within the airline, but the information did not reach a wider system that could have warned the entire industry about the danger.

Flight 514 left behind 92 dead, but the investigation led to a series of changes designed to prevent a similar disaster from happening again. One of the most important was the requirement to install a Ground Proximity Warning System (GPWS) on passenger planes. The TWA plane was not equipped with such a system. It had another altitude warning, but it did not provide the crew with enough time to avoid hitting the mountain. The NTSB determined that a system similar to GPWS could have prevented the accident. Following the disaster, the FAA mandated the installation of such systems in the commercial fleet.

The way air traffic controllers and pilots spoke also changed. Instead of a clearance that could be interpreted in several ways, controllers began using more explicit instructions, clarifying at what altitude the plane should remain and until what point. Approach charts and altitude definitions were also improved to reduce the possibility of confusion.