Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Landed in Emergency Condition; General Maintenance Action
Aircraft
Crew was alerted by a red Master Warning; CABIN ALT; and CABIN ALTITUDE lights illuminated; triple chime alarm and EICAS message CABIN ALTITUDE displayed.  Crew observed the cabin altitude increasing through 11000 ft climbing 500-1000 feet per minute. Immediate action checklist items were accomplished; ATC clearance for an immediate descent obtained. Cabin altitude continued to increase however; stabilized at approximately 13;000 ft as the aircraft descended in an idle power; full speed-brake; 250 to 300 kt IAS; wings level descent. During the wings level stabilized descent with flight spoilers; the cabin pressure descended below 10;000 ft and seem to stabilize at various lower altitudes upon aircraft level off at 13;000 ft for terrain. Captain transferred pilot flying responsibilities and ATC communications to the First Officer. Crew elected to divert. Remaining Cabin Altitude Warning checklist items were completed; ATC clearance to divert obtained; company and Station Operations notified. Inflight coordination; flight attendant cabin inspection; diversion checklist completed and passengers advised of the situation during the descent and Captains decision to divert. Terrain was insight throughout the descent; approach and landing accomplished. No assistance was required after landing or during taxi to the gate.
[Report narrative contained no additional information.]
B757 flight crew reported a loss of pressurization while at cruise altitude. An immediate descent was initiated and a successful diversion to a suitable airport was accomplished.