B737-800
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft
During a FCF (Functional Check Flight) evaluation flight; while accomplishing the 'cabin altitude warning horn' FCF checklist; the pressurization controller appears to have malfunctioned in all modes (auto; alt and manual). The true aircraft diagnosis is still to be determined; as maintenance is working the problem. An expedited descent was accomplished; unfortunately the pax oxygen masks deployed during the descent.
During FCF (Functional Check Flight) evaluation; cabin altitude warning check; the cabin outflow valve became unresponsive (in auto; alt; and manual); causing the cabin rate of climb to increase above the limitation. An expedited descent was accomplished; but the passenger oxygen masks still deployed.
B737 flight crew; while performing a post maintenance functional check flight; discovered the cabin pressure controller failed in all modes while testing the cabin altitude warning horn. A rapid descent was initiated and the flight returned to the departure airport.