A war engulfing the Middle East has "cleared the region's skies," forcing airlines to make drastic rerouting plans and leaving a huge void in the usually busy global airspace.
With Israel and the US bombing Iran day after day - and Tehran responding with waves of missile and drone attacks - airlines have been forced to divert their passenger planes away from the Gulf or risk a catastrophic accident.
How was the airspace closed?
The world's airspace is divided into Flight Information Regions (FIRs), which broadly follow international borders.
Governments are usually responsible for the regions above them, providing air traffic services.
In an extreme situation, such as a regional war, authorities will notify aircraft that they are restricting or closing their FIRs by issuing a notice called a Notam, or Notice of Air Missions.
Numerous FIRs in the Middle East have been closed since the bombing began, creating a 2.8 million square km (1.08 million square miles) vacuum:
But it's not just governments that "empty the skies."
Airlines make decisions about where not to fly based on a number of factors, including warnings from the countries where they are registered (such as the United Kingdom for British Airways or India for Air India) and whether their insurers will cover a flight over dangerous areas.
And dispatch teams constantly monitor events to ensure safe routes.
"Ultimately, the decision whether a piece of airspace is safe to fly your passengers through is that of the airline and airline dispatchers, depending on the level of risk," says former British military pilot and aviation expert David Learmount.
This explains the situation in the largely empty airspace over Lebanon, which is being hit by Israeli attacks, the article says. The Guardian, the Telegraph reports.
While Lebanon's FIR is not technically closed, most airlines will not risk flying there.
What have the airlines done?
There have been significant changes in the main Middle Eastern routes connecting Europe, Africa and Asia.
When the bombings began on Saturday, airlines were able to immediately begin rerouting, like a flock of birds, as there has been contingency planning for years, in which Middle Eastern routes avoiding “some hot spots” were already planned.
In many cases, jet planes would have these routes pre-programmed into their navigation systems.
Two main rerouting options have emerged for airlines - one that passes north into the Caucasus but under closed Ukrainian airspace, and the other that channels air traffic south through Egypt, but also Saudi Arabia and Oman, which are experiencing intermittent attacks.
These corridors are "absorbing" the displaced traffic, but they are also creating a bottleneck, which explains why delays and cancellations are increasing.
"This problem is not getting better, it's getting worse," Learmount said. "You can see the patterns of how the planes are moving..."
Why are some flights operating?
Major airports in the region, including the world's busiest international transit airport, Dubai, have been largely closed for days.
Domestic carriers Emirates, Qatar Airways and Etihad Airways have been deeply affected.
However, limited operations have begun to resume for repatriation and essential transit.
This can happen under strict conditions. For example, the Emirates FIR is partially closed, but flights can operate with special permission.
This is why random flights can be seen flying in seemingly closed airspace on flight tracking websites.
Oman's airspace also remains open, despite several attacks.
What is the impact?
Delays, cancellations and huge financial costs.
Here is a graph showing the extent of the impact on the main operators in the region:
Steve Fox, operations control director at the UK's leading air traffic control services provider Nats, said in a blog post that the "huge black hole" in Middle Eastern airspace was creating a situation in which airlines had "significantly longer routes, flight times and fuel supplies".
All of this costs money, and there has been a sell-off of airline shares.
What seems certain, Fox wrote, "is that things will be uncertain for a while." /Telegrafi/
