What happened
While cruising at 33,000 feet, the cabin altitude warning horn activated. The captain identified that the right air conditioning pack had shut off. In an attempt to restart the pack, the captain and the flight engineer performed troubleshooting steps without utilizing a checklist.
As the cabin altitude rose to 14,000 feet, warning lights illuminated and oxygen masks deployed throughout the cabin. During the efforts to correct the cabin altitude, the flight engineer accidentally opened the outflow valve, which triggered a rapid loss of cabin pressure.
The resulting hypoxia caused the captain, the flight engineer, and the lead flight attendant to lose consciousness. The captain's loss of consciousness was attributed to a delay in donning his oxygen mask. The flight engineer lost consciousness after providing assistance to revive the flight attendant.
The first officer, who possessed 10 hours of experience in the aircraft, donned his oxygen mask immediately upon the initial warning horn sounding. Because he remained conscious, the first officer was able to initiate an emergency descent. During this descent, the captain, flight engineer, and flight attendant regained consciousness, allowing for an emergency landing at Indianapolis, Indiana. There were no injuries reported.
The investigation
The aircraft underwent inspection and flight testing the following day. The investigation found that the airplane's pressurization system functioned with no anomalies.