British airline pilots are threatening to refuse to fly to most of eastern Europe and Asia, including the Indian sub-continent and China. Insiders describe Africa as a "no-go" area, and Central and South America are causing anxiety.
A study conducted by the British Airline Pilots' Association (Balpa) has found serious shortcomings in most countries' preparations, especially those in the developing world.
Unless there is a rapid acceleration in the drive to make air traffic control systems "millennium compliant", flights from British airports will be severely restricted from 31 December to 3 January.
Balpa said it would be safe to go to north and west Europe, and the United States. However, some US authorities have questioned the readiness of airports dealing with internal flights. It is understood that pilots will refuse to fly over countries where they believe little or no attempt has been made to cope with the potential problems.
A list of airports and regions thought to be unsafe will be published in the next few weeks by the pilots' union with the help of the International Federation of Airline Pilots' Associations. A Balpa source said: "People will not have to worry about travelling from Britain to a country over the millennium ... we will not fly to areas we regard as unsafe."
Christopher Darke, general secretary of Balpa, and the Transport and General Workers' Union, will fully back those refusing to fly on safety grounds over the new year. He said: "We are monitoring the situation very carefully and we will keep our members and the travelling public informed. We are determined to ensure their safety."
Demand for intercontinental flights from Britain could be low over the four-day period as many holidaymakers will leave earlier in the week and stay away until after the new year.
The International Air Transport Association is also running an inquiry, to be published in the summer. A spokesman at British Airways - which supplied the chairman for the inquiry, and which has spent pounds 100m on checks - said it would not know which were safe routes until the report was finished.
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