B737-800 Air Return due to Cabin Pressure

A Jeju Air Boeing 737-800, registration HL8332 performing flight 7C-4604 from Angeles (Philippines) to Seoul (South Korea) with 149 people, was climbing out of Angeles when the crew stopped the climb at about FL210 due to problems with the cabin pressure and performed a rapid descent to FL100. The aircraft returned to Angeles for a safe landing on runway 20L about 40 minutes after departure. Passengers reported it became very cold in the cabin while the aircraft was climbing, then the oxygen masks dropped from the cabin ceiling. The airline reported a number of passengers complained the oxygen masks did not work, however, those passenger had not pulled down their mask to activate the oxygen generator (editorial note: a common misconception is, that the plastic concentrator bag at the mask should inflate while the mask operates, however, this is not necessarily the case).