Pilot fatigue may be clue to 50-year-old UN mystery

Three investigations failed to explain the plane’s plunge, feeding conspiracy theories involving superpower rivalries.

But aviation experts now say the most likely explanation is a danger foremost in the minds of today’s air crash investigators, but unknown 50 years ago – pilot fatigue. An obscure Swedish technocrat, Mr Hammarskjold was an unexpected second head of the United Nations in 1953.

But he personally negotiated the release of American soldiers captured in the Korean War, sent UN peacekeepers to the Suez Canal and tried to resolve the civil war in Congo, which had won independence from Belgium.

He is still considered the most effective secretary-general the UN has ever had.

But he angered many governments. Congo was a land in chaos that 20,000 UN troops were trying to stitch back together.

Several countries coveted the mineral wealth of the breakaway province of Katanga, and feared the Congolese government would nationalise those resources if the country were reunited.

When the Douglas DC-6B flying Mr Hammarskjold went down on 18 September, 1961, conspiracy theories emerged.

Did the US have him killed? Perhaps Belgian agents sabotaged the plane, or British fighters shot it down? Each country had a stake in Congo’s mineral resources, and stood to lose if a peace deal was struck.

Mr Hammarskjold’s crashed as he was trying to negotiate an agreement between the government of Congo and Katanga. The wreckage was not found until 15 hours later, near Ndola Airport in Northern Rhodesia, now Zambia.

Three inquires, two by Rhodesia and one by the UN, failed to determine the cause.

“By using modern fatigue models, we can show that the schedule that this crew flew on the day of the accident would have made them tired to a point of impairment when the accident occurred,” said William Voss, head of the Flight Safety Foundation.

He said rest-impaired crews often have events of “micro-sleep” when they effectively fall asleep for a few moments.

It has never been established precisely how much flying Captain Per Hallonquist and First Officers Nils-Eric Aahreus and Lars Litton had done in the preceding weeks, but Bengt Rosio, Sweden’s representative in Congo at the time, said: “All UN pilots just flew much more than they wanted to.”

On that fateful day, the pilots waited 12 hours for Mr Hammarskjold at the airport in Leopoldville – today known as Kinshasa – before the seven-hour night flight to Ndola.

“Fatigue is a very serious issue today, but in those days there was no understanding of its impact,” said Gideon Ewers, spokesman for the International Airline Pilots Association. “There were no duty time limitations. Pilots essentially flew until they fell asleep.”

The UN accident report, released in 1962, conjectured that an error by the pilots was the likely cause. But the report failed to explain how or why the pilots had erred so disastrously on the final approach.

The plane had no flight data or cockpit voice recorder and the probes found no foul play.