Commercial Fixed Wing
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 149.13; Flight Crew Total 17500; Flight Crew Type 11000
Time Pressure; Communication Breakdown; Distraction; Workload
ATC Issue All Types; Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; Flight Crew Diverted; Flight Crew FLC complied w / Automation / Advisory; General Maintenance Action
Aircraft
Normal takeoff right seat [as] Line Check Airman. Level FL360 at 10 minutes red Cabin Altitude EICAS with Aural Warning. Cabin at 10;500 feet but not climbing significantly. Transfer flight controls to left seat pilot; ran cabin altitude QRC and started [priority] descent to 15;000 feet. ATC advised. After switching to auto 1 cabin controller; seemed to stabilize at at FL240 and warning light went out on EICAS; cabin seemed to descend. Due to terrain and a stable cabin we climbed to FL190. Thunderstorm avoidance and normal approach and landing to [Runway] XXR back at ZZZ. Left seat pilot made landing. Initially; the Controller did not hear [us advising] had to [re-advise] at 15 minutes into event. Cabin was stable but fluctuating inbound. On the ground; the mechanics came to the cockpit to tell us the main PC air distribution duct was broken and not connected. This caused the inability for the aircraft to pressurize.
Air carrier Line Check Airman reported loss of pressurization. The crew switched pressurization controllers and returned to the departure airport.