A Virgin Atlantic pilot was removed from a transatlantic flight after failing a breathalyser test. He has finally been cleard of this charge after it was discovered that his low-carbohydrate diet triggered a false reading.

Subsequent blood tests on the pilot showed a blood-alcohol reading of just over a fifth of the limit set for airline pilots - which in turn is a quarter of the drink-drive level.

The pilot's nightmare began when he went through the security checks for flight crew one of the guards thought he could smell alcohol on his breath.

The pilot was allowed to board the plane but about 45 minutes before take-off police got on the aircraft and breathalysed the pilot in the cockpit using a machine calibrated to aviation levels. The pilot failed this test and was escorted off the plane.

A standby crew was called and the pilot was taken to the police station, where blood tests were taken.

He was suspended from duty and released on bail.

The pilot's blood was sent it to a laboratory where they found only a minimal blood alcohol reading. After the lab tested two more samples, he was exonerated.

Even non-drinkers are capable of producing trace elements of alcohol in their bloodstream, which would explain the level in the pilot's blood.

The breathalyser reading was attributed to the pilot's low–carbohydrate diet, which can affect the smell of a person's breath and their metabolism.

Breathalysers mainly detect ethanol (the type of alcohol found in drinks) But some machines are unable to distinguish ethanol from acetone, a chemical that is produced by people on low-carbohydrate diets such as the Atkins diet. In normal circumstances this is not a problem but with the alcohol limit in the aviation industry is set at about a quarter of the normal "intoxication" level (.02) even these traces can result in a positive reading.

Where this is most likely to cause problems is when a person has been drinking, but not to the level of being intoxicated (.08). You then add the fact that the person is on a low carbohydrate diet, which will produce acetone in their breath, and there is a strong likelihood you will end up with a unreliable result from the breath testing machine.

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