Thousands of flights have been delayed, disputed or canceled by the closure by Pakistan of its airspace for commercial flights after tensions escalated with India.
Its airports will only be used for "military purposes" until the airspace is reopened for commercial activities.
Pakistan airspace lies directly in the path on the major air route between southern Asia and Europe and many flights are already at the limit of their range - particularly in the northern winter with stronger headwinds.
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Flights have been diverted south of Pakistan across the Arabian Sea putting more pressure on the heavily used corridor.
Pilots are not able in many cases to get the levels they want because of the congestion increasing fuel burn.
Some flights have been forced to land to get extra fuel while others will take longer to get to their destination.
Many airlines have also canceled services.
Passengers are urged to check with their airlines.
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