Aviation regulator Directorate General of Civil Aviation (DGCA) has initiated a probe into the incident, which happened this morning, sources said.
The probe would look into the reasons for the incident on Jet Airways flight 9W-820, which could also be because of some maintenance issue, they said.
The aircraft remained airborne for almost twenty minutes before landing back at the Chennai airport at around 1030 hours, they said.
The oxygen masks drop when the cabin pressure goes down beyond a particular limit. But in today's incident, this was not the case.
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Jet Airways, in a statement said that the flight came back to Chennai without completing its journey due to accidental dropping of the oxygen masks.
"Flight 9W 820 from Chennai to Delhi made an air turn back due to accidental dropping of oxygen masks in two rows of seats and landed in Chennai," the airline said.