Reports that a Jet Airways aircraft flying to Brussels suddenly dropped 5,000 feet over Ankara in Turkey are being investigated by India’s aviation authority.

The civil aviation ministry said Jet Airways pilots had been “taken off the roster pending inquiry,” according to the BBC.

Jet Airways, India’s second largest airline, said it was co-operating with the investigation.

The Times of India reported the pilot was taking “a nap, as per rules”, and the co-pilot was “busy on her tablet”.

“The co-pilot, who was supposed to hold fort in the cockpit, claims she was busy on her tablet and did not notice the aircraft had lost altitude,” according to the newspaper.

The aircraft was pulled back to its assigned height after the co-pilot received an alert from an air traffic controller.

The aviation watchdog – the Director General of Civil Aviation (DGCA) – said it viewed the descent as “a serious incident”.

The pilots have been questioned and a “detailed investigation” been ordered.

Jet Airways said it had also initiated an “internal inquiry”.

The incident occurred last Friday on a Jet Airways’ flight to Brussels from Mumbai.