The captain of an Air India flight from Phuket to Delhi that experienced a sudden loss of altitude last week returned an initial screening result for psychoactive substances, prompting further laboratory testing, India's civil aviation ministry confirmed.

The aircraft experienced a sudden loss of about 300ft in altitude while cruising, before stabilising and landing safely in Delhi, on 4 August.

In the wake of the incident, flight crew members underwent standard psychoactive substance screening. The pilot-in-command's initial screening indicated a result that necessitated confirmatory testing. Samples were dispatched to a designated laboratory, with the final report pending. The Directorate General of Civil Aviation grounded both crew members pending the investigation's outcome.

The incident has been officially classified as “serious” and put under investigation by the Aircraft Accident Investigation Bureau.

The ministry did not disclose the specific substance, if any, indicated by the initial screening.

Air India said it was aware of the post-flight screening tests conducted under applicable protocols, but had not been informed of the results. “We are aware that a post-flight screening test was conducted on the pilots in accordance with applicable protocols,” an airline spokesperson said. “However, the results of the test have not been shared with Air India, and we are therefore not in a position to comment on any findings."

The airline added that it conducted regular drug testing of crew members in compliance with civil aviation regulations and would continue to cooperate with authorities.

The incident comes amid heightened scrutiny of India's aviation sector, following a series of safety-related investigations and regulatory reviews.