Captain of an Air India flight that suddenly lost altitude last week is undergoing further laboratory testing after an initial screening indicated a result requiring confirmation.
India's Civil Aviation Ministry said the Airbus A320 was flying from Phuket to New Delhi on August 4 when it lost around 300 feet of altitude during cruise.
The aircraft stabilised and later landed safely in Delhi.
Under standard procedures, both pilots underwent screening for psychoactive substances following the incident. The initial result for the pilot-in-command prompted samples to be sent to a designated laboratory for confirmatory testing.
The ministry did not disclose what substance, if any, was indicated by the screening and said the final laboratory report is still awaited.
Both pilots have been taken off flying duties by India's Directorate General of Civil Aviation while the investigation continues.
The incident has been classified as serious and is being investigated by the country's Aircraft Accident Investigation Bureau.
Air India said it was aware that post-flight screening had been carried out but had not been informed of the results. The airline said it would continue to cooperate with authorities.
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