B767-300 and 300 ER
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; General Maintenance Action
Aircraft; Procedure; Human Factors
About 10 mins after leveling off at our final cruise altitude of FL360; we received a CAB ALT alert and warning. After donning our oxygen masks and accomplishing the appropriate QRH procedure; we determined that our altitude was uncontrollable and requested descent to 10;000 feet. After conferring with Dispatch; we [returned] to our origin airport.
Cruising at FL360; the CAB ALT light and master warning light and horn went off. I had turned the right pack off out of 4;000 feet MSL; so I immediately turned the right pack to AUTO as I simultaneously donned my oxygen mask and established crew communication. We accomplished the CABIN ALTITUDE or Rapid Depressurization checklist. The cabin altitude remained uncontrollable; so we descended to 10;000 feet. The company advised us to return to [departure airport]; which we did without further incident.
B767-300 flight crew reported returning to departure airport after experiencing loss of cabin pressure.