How much alcohol is too much for a pilot who's about to take flight?
Believe it or not, the answer varies depending on where your flight departs from -- and where it lands.
There are no standardized international rules on pilot alcohol consumption and testing. Instead, the International Civil Aviation Organization issues guidance and then countries set their own regulations, limits, testing regimes and punishments.
Despite being a rarity, it's an issue that has received extra attention after a series of high profile incidents. In late December, a pilot was found passed out in the cockpit before a scheduled Boeing 737 flight in Canada. In mid-2016, two pilots were arrested in Scotland on suspicion of violating alcohol rules before a flight to New Jersey.
The December arrest prompted Canada to take another look at its rules. The European Union is also considering changes.
Here's a look at how the rules work:
Who can fly
In India, which boasts the world's strictest rules, pilots aren't allowed to drink within 12 hours of a flight and must have absolutely zero alcohol in their system.
"0.001% is also a violation," said Lalit Gupta, a senior official at India's Directorate General of Civil Aviation.
In the U.S., pilots are allowed to have a trace amount of alcohol in their system -- up to 0.04% blood alcohol concentration -- and must have eight hours between "bottle to throttle". (The 0.04% level is half the 0.08% legal limit for U.S. drivers on the roads.)
Who gets tested and when
Alcohol testing also varies by country: India subjects pilots to a breathalyzer test before each of its 2 million annual flights, while the U.S. conducts between 11,000 to 13,000 random alcohol checks in a typical year.
The U.S. tests caught 10 pilots violating the rules in 2015.
India's stricter regulations caught 46 pilots in 2016, according to the country's Directorate General of Civil Aviation.
"If you set a zero percent tolerance limit and test everyone, you're going to have more positives," said James Stamp, global head of aviation at KPMG. "It's just a fact."
In Europe, each nation sets their own alcohol rules and then airlines develop and implement compliance procedures.
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Safety risk
Testing can help ground pilots before they do any real damage. But there are still documented cases of alcohol contributing to aviation accidents.
The most comprehensive data, from consulting firm JACDEC, showed there were 11 commercial aviation accidents linked to alcohol since 1980, out of a total of nearly 12,000 incidents.
The private accident-tracking group Aviation Safety Network counted five global commercial aviation accidents linked to alcohol since 1980.
The most recent documented commercial incident occurred in east Russia in 2012. A small plane crash killed 10 of the 14 people on board, and alcohol was later found in the blood of its two crew members.
An earlier Russian crash, in 2011, killed 47 people. The incident was linked to alcohol, leading authorities to revoke the airline's license.
Still, only a tiny fraction of aviation accidents are linked to alcohol.
"Let's be fair, air travel has become an extremely, extremely safe way of travel," said Jan Richter, founder of JACDEC.
That's a sentiment echoed by pilots unions, which defend current regulations as sufficient.
"Instances of substance abuse are extremely rare among the approximately 100,000 professional airline pilots in the United States who safely fly passengers and cargo on more than 27,000 flights every day," the U.S.-based Air Line Pilots Association said in a statement.
New regulations?
Stricter regulations are on the way, however, in some countries.
Canada's transport minister has pledged to "enhance aviation safety" after the December incident in which a pilot was charged with having control of an aircraft while impaired.
Europe's top regulator is also expected to introduce rules requiring more systematic alcohol tests later this year.
The changes are a response to the 2015 Germanwings crash that killed 150 people. The plane's co-pilot, who was being treated for depression, crashed the aircraft into the French Alps. The crash has not been linked to alcohol, but it prompted officials to get more serious about testing pilots to ensure they're fit to fly.
Russia is also reportedly considering stricter pilot testing, but the country's regulators did not respond to requests for comment.
The modern U.S. rules on testing were implemented in response to several alcohol-related accidents in the late 1980s.
Crime and punishment
There are also differences in the punishments doled out to pilots found to be violating alcohol rules.
In India, pilots have their license suspended for three months after a first offense, and three years after a second offense. A third offense means they're booted from the profession for life. India does not offer a rehabilitation program for pilots.
Meanwhile, pilots caught in the U.S. are more likely to face criminal charges and must reapply for their pilot's license after successfully completing a rehab program.
The U.S. substance abuse program for pilots is run by industry unions, aviation firms and the Federal Aviation Administration. The program has helped rehabilitate over 4,500 professional pilots, according to the program's administrators.
-- Rishi Iyengar, Sugam Pokharel, Medhavi Arora, Jon Ostrower and Serenitie Wang contributed reporting.
