Passengers on a Jet Airways flight in India suffered nosebleeds and ear pain after the flight crew reportedly forgot to flick a switch to maintain air pressure on the plane.
Oxygen masks dropped down during the emergency incident on board Flight 9W697 from Mumbai to Jaipur, before the plane landed safely.
There were 166 passengers and five crew on board the Boeing 737.
Passengers received medical care once the plane had landed back in Mumbai.
The aircraft stopped climbing at 11,000ft, before returning to the airport, according to the Flightradar24 aviation tracking website.
Passenger Darshak Hathi said there was also a problem with the air conditioning on the aircraft after it took off.
The Press Trust of India news agency quoted an official as saying the malfunction occurred during the plane's climb.
It was heading to Jaipur, a tourist destination and the capital of Rajasthan state.
Jet Airways has said the flight's cockpit crew has been taken off scheduled duties pending an investigation.
Lalit Gupta, a senior official at India's aviation regulator, told the Hindustan Times newspaper that the crew had forgotten to select a switch to maintain cabin pressure.