A growing number of global airlines are currently re-routing flights to avoid airspace controlled by Iran above the Strait of Hormuz and the Gulf of Oman, after the United States aviation regulator barred American carriers from the area until further notice.
Thursday's emergency order from the US Federal Aviation Administration (FAA) came after Iran shot down a high-altitude US military drone with a surface-to-air missile, sparking concerns about a serious threat to the safety of commercial airlines.
The downing of the unarmed Global Hawk drone - which can fly at altitudes up to 18,300m (60,000ft) - was the latest in a series of incidents that included explosive strikes on six oil tankers in the Gulf region, a critical juncture for the global oil market.
According to flight-tracking applications, the FAA said, the nearest civil aircraft was operating within about 45 nautical miles (83km) of the drone when it was shot down.
"There were numerous civil aviation aircraft operating in the area at the time of the intercept," the FAA said, adding that its prohibition would remain in place until further notice.
Hours earlier, United Airlines suspended flights between New Jersey's Newark airport and India's financial capital of Mumbai following a safety review.
British Airways, Germany's Lufthansa, KLM of the Netherlands, Australia's Qantas Airways Limited, Cathay Pacific, Singapore Airlines Limited, Malaysia Airlines and Emirates Airlines all said they were re-routing flights to avoid the area.
Amy Myers Jaffe, senior fellow at the Council on Foreign Relations, said, "Bypassing Iranian oil space can add to jet fuel costs, first off, so it definitely affects international carriers' bottom lines. It is a double whammy because oil prices are higher, and operating costs for bypass routes are higher."
She told Al Jazeera that the June 12 missile strike by Houthi rebels in Yemen on a southern Saudi commercial airport's arrivals terminal and a missile strike two days ago on oil infrastructure in southern Iraq would "alert airlines to the fact that an escalation in conflict could impact regional airports".
"The risk of continued attacks has to be one that airlines take into account in assessing the risks of various routes," said Myers Jaffe.
The FAA said it remained concerned about the escalation of tension and military activity in close proximity to high-volume civil aircraft routes, as well as Iran's willingness to use long-range missiles in international airspace with little or no warning.
In July 2014, Malaysia Airlines Flight MH17 was shot down by a missile over Ukraine, killing all 298 people onboard and prompting carriers to take more steps to uncover threats to their planes.
But concerns persist over inadequate government intelligence sharing and a reluctance by countries involved in conflicts to divulge information or sacrifice overflight fees by closing their skies, according to safety experts.
US ban does not apply to all carriers
The US ban does not apply to airlines from other countries. However, OpsGroup - which provides guidance to operators regarding global hot spots - said carriers globally would take it into consideration.
"Since MH17, all countries rely on advice from the US, the UK, France and Germany to highlight airspace risk," it said.
"The threat of a civil aircraft shootdown in southern Iran is real," it added.
Restricting airspace complicates airlines' efforts to keep routes running in a region where airspace is already congested, in part due to ongoing violent conflicts that have made it unsafe to fly over some countries.
At 14:00 (GMT) on Friday, flight tracking app Flightradar24 showed Qatar Airways flights routinely flying through the area barred to US carriers.
On Monday, before the drone was shot down, Qatar Airways Chief Executive Akbar al-Baker told the Reuters news agency that the airline "has a very robust plan B for any eventualities, including if there is a conflict in our region".
Etihad Airways, which according to Flightradar24 was also flying over the area earlier, said it was monitoring the situation and had also adopted contingency plans.
The airline agreed "to change a number of the flight paths we operate to and from the Arabian Gulf" after close consultation with the UAE General Civil Aviation Authority.
Emirates is re-routing all its flights away from areas of possible conflict in the Gulf, a spokeswoman said on Friday, and Flydubai said it has adjusted some of the existing flight paths in the region and will make further changes when necessary.
United Airlines said it had suspended its flights to India through Iran airspace after a "thorough safety and security review", but did not say how long the suspension would last.
A United Airlines spokesperson said customers flying from Mumbai to Newark would be booked on alternative flights back to the US.
"We continue to explore all our options and remain in close contact with relevant government authorities," he added.
A Lufthansa spokesperson said the company's planes had been avoiding the Strait of Hormuz since Thursday. He added that Lufthansa had extended the no-fly zone over parts of Iran on Friday. But the airline was apparently still serving Iran's capital, Tehran.
British Airways says it will adhere to FAA guidance, avoiding Iranian airspace by using alternative routes.
Dutch carrier KLM was no longer flying over the Strait of Hormuz, a spokesperson said on Friday, while British Airways said it would adhere to the FAA guidance and use alternative routes.
Malaysia Airlines said it was avoiding the airspace, which it had previously used on flights from Kuala Lumpur to London, Jeddah and Medina.
"The airline is closely monitoring the situation and is guided by various assessments, including security reports and notices to airmen," it added.
Qantas said it was adjusting flight paths to avoid the Strait of Hormuz and Gulf of Oman until further notice. Singapore Airlines said some flights might require longer routings to avoid the area.
Cathay Pacific said on Friday that its planes will not fly in the airspace above the Strait of Hormuz and it will review areas of concern to ensure all routes remain safe
On Thursday, two other US carriers, American Airlines and Delta Air Lines, said they did not fly over Iran. Japanese carriers Japan Airlines Co Ltd and ANA Holdings Inc also said they did not fly over the area.
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