Cause Unknown

What brought down these five airplanes?

Reconstruction of a South African Airways Boeing 747 has failed to reveal what started an onboard fire, which led to the loss of 19 crew members and 140 passengers. (Courtesy BEELD)
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Commercial aircraft are customarily equipped with several altimeters, both barometric and radio. According to the NTSB, the barometric altimeter might have been malfunctioning or the pilots might have been relying too much on the radio altimeter in an area of uneven terrain. The crash would likely have been averted if the cockpit had been equipped with a Ground Proximity Warning System, which is now required in all airliners in the United States.

South African Airways Flight 295

South African Airways’ Helderberg was a Boeing 747 Combi, an airliner whose main deck could be partitioned to carry both passengers and cargo. On November 28, 1987, the Helderberg was carrying 140 passengers, 19 crew members, and six pallets of cargo on a flight from Taipei, Taiwan, to Mauritius and then on to Johannesburg, South Africa. Less than an hour before the estimated arrival in Mauritius, Flight 295 reported smoke in the aircraft. Controllers could hear the pilots struggling with the emergency before communications went out. The Helderberg crashed in the Indian Ocean. No one survived.

Search aircraft and vessels retrieved a small amount of floating wreckage and human remains, but most of the debris settled at the bottom of the ocean. More than a year after the accident, a deep-sea salvage operation retrieved the cockpit voice recorder and a substantial quantity of wreckage. The recorder tape provided some information, primarily showing how rapidly the aircraft’s systems were compromised, but it was not as revealing as hoped. South African investigators concluded that fire had broken out in the Helderberg’s right forward cargo pallet and been fed by plastic and cardboard packing materials, but the ignition source remained unknown.

The Helderberg disaster was controversial because of the apartheid policy of the government that owned the airline. Initial supposition was that Flight 295 was the victim of anti-apartheid sabotage. But when the government’s own investigation found no evidence of explosion, suspicions shifted. Conspiracy theories to this day hold that the Helderberg carried dangerous cargo not listed on the manifest, and that the government of the time was using commercial aircraft such as the 747 to circumvent the international arms embargo against the white-controlled regime.

Payne Stewart Learjet 35

All aircraft accidents are terrifying, but the story of the last flight of professional golf champion Payne Stewart has an added element of strangeness. It was an incident that unfolded over nearly four hours and 1,500 miles. Stewart, known for competing in the colorful golfer attire of an earlier era, had won the U.S. Open for the second time four months before he boarded a Learjet 35 on October 25, 1999. He, two agents who represented him, and a golf course designer were flying from Orlando, Florida, to Dallas, Texas.

The flight had a two-pilot crew, and for eight minutes after takeoff, their radio messages were routine. But when communications suddenly ceased and the aircraft began to veer off course, military aircraft were dispatched to intercept. F-16 pilots found the jet with opaque cockpit windows, dark interior, and unmoving flight controls. With the autopilot apparently following an unchanging course, the ghost ship cruised above 46,000 feet until it exhausted its fuel and spiralled into a South Dakota field. The jet hit the ground at a steep angle and near-supersonic speed, shattering at impact.

From the start, the Learjet’s performance, the frosted windows, and the crew’s unresponsiveness made clear what led to the crash: crew incapacitation from hypoxia, stemming from cabin pressure loss. What could not be determined is why the cabin lost pressure. Also unknown is whether the pilots were using the aircraft’s supplemental oxygen, and if so, why it failed to keep them conscious long enough to act. Unfortunately, the aircraft carried no flight data recorder, and its cockpit voice recorder could capture only the last 30 minutes of the flight.

Lester A. Reingold worked for seven years at the National Transportation Safety Board. He thanks airline historian Robin MacRae Dunn for his contributions to this article.

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