Everyone knows that smoking on board planes is totally banned.

Yet in a story you’d have to file under ‘you can’t make this up’ a pilot on board a major airline was smoking an e-cigarette in the cockpit.

And that sparked an absolute fiasco with the plane dropping 25,000ft in just 10 minutes.

Here’s what happened according to the South China Morning Post.

The wayward pilot on the Air China flight was using the e-cigarette when the co-pilot decided to turn off the circulation fan to prevent the smoke from reaching the cabin so the other crew members and passengers would realise what was going on.

But the co-pilot accidentally turned off the air conditioning unit, causing oxygen levels to plummet and forcing the plane’s emergency descent.

This was confirmed by Qiao Yibin from the safety office of The Civil Aviation Administration of China.

He said: “The co-pilot mistakenly switched off the air-conditioning unit that was next to it (the circulation fan), resulting in insufficient oxygen in the cabin and an altitude warning.

"At present, we are investigating the cause in greater detail and if the investigation proves it is true we will handle it according to the law and regulations and deal with it seriously."

Air China's website says smoking is strictly prohibited on all its flights. It is clearly stated that e-cigarettes are also banned and will deal with the incident with zero tolerance.

In a statement the airline said: “After an investigation to verify the incident, the decision is to suspend the related crew from flying and terminate the contracts in accordance with the law. The crew members who are responsible for the incident have been seriously dealt with.”

Half-an-hour after the flight carrying 153 passengers and nine crew members left Hong Kong International Airport, oxygen masks dropped from the ceiling and the plane descended to 10,000 feet as it was travelling between Shantou and Xiamen.

The Boeing 737 later climbed back to 26,000 feet and arrived safely at its destination. No injuries were reported and the aircraft was not damaged.

For more on this go to https://www.scmp.com/news/hong-kong/community/article/2155119/air-china-co-pilot-was-smoking-e-cigarette-and-made-error 

* AvSax fire containment bags are now on board several major airlines worldwide and were deployed 27 times in 2017.

If an electronic device – and that includes e-cigarettes - starts to seriously overheat or emit smoke the cabin crew will pour at least two litres of water into an AvSax. It is imperative to first knock down the flames from the device using an on board halon fire extinguisher, then transfer the device into AvSax before it reignites. Additional water is then required. The water activates the polymer gel inside the bag causing it to expand around the device. Should the device keep on venting then the AvSax is tough enough to absorb the energy.

The AvSax cools the batteries in the device, reducing the likelihood of the battery igniting but if it does go into thermal runaway it is all contained within the bag.

Amazingly, the water is absorbed into the internal lining of the bag so the device is dry when it is removed.