Date: 201811
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: A300
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Air Conditioning Distribution Ducting; Clamps; Connectors
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Received an ECAM cabin altitude warning as we leveled at cruise altitude (FL350). I directed the donning of oxygen masks. Cabin altimeter showed cabin was climbing through 10;000 feet. After crew and jumpseater had checked in on intercom; we began an immediate descent and turned back toward [departure airport; after I] (coordinated with Center). I directed the FO (First Officer) to descend at 320 knots until we leveled off (initially cleared to 7;000 feet; then 5;000 feet). We made an initial reaction to manually close the outflow valves to stop the cabin from climbing. Outflow valves were already indicating full closed. Cabin continued to climb to at least 12;000 feet. Completed ECAM items and referred to QRH for CAB PRESS MAN CTL; which basically directed the same actions. Passing through 10;000 feet; cabin and aircraft altitude matched; and we removed our masks. FO had a tough time with mask; as one of the connection points was disconnected. I directed the FO to continue above 250 KTS below 10;000 feet. I assessed that the pressurization system was not responding to manual outflow control--appeared to be unpressurized between 10;000 feet and 5;000 feet in the descent; matching cabin altitude; outflow valves full closed. I discontinued CAB PRESS MAN CTL procedure for this reason. We completed an uneventful landing. We taxied to parking. During taxi in; we noticed that the aircraft was pressurized. We used manual control to relieve the pressure before opening the door. I am not sure at what point the aircraft pressurized--at some point between 5;000 feet and taxi in. In hindsight; I could have avoided this by completing the CAB PRESS MAN CTL procedure; as it directs opening of the outflow valves before landing after cabin pressure and aircraft altitude were equal. This was a mistake on my part. At the time; I felt that the aircraft was not pressurized and could not pressurize. I chose to focus on a safe landing instead of continuing with the final steps of the procedure. FO did a great job! Entries made in [maintenance log] for cabin altitude and FO oxygen mask.


Second narrative: After passing FL340 for FL350; an ECAM warning announced that cabin altitude was in excess of 10;000 feet. A check of the cabin altimeter confirmed the cabin altitude was passing 10;000 feet and going up. Both pilots put on oxygen masks and the Captain announced to the jumpseater to put his on as well. The mask of the First Officer had a broken strap which required the FO (First Officer) to have one hand on the mask at all times to maintain the seal. Captain followed ECAM guidance to manually control cabin pressure; but cabin altitude kept climbing. The Captain decided to turn back and commanded an emergency descent to 10;000 feet with coordination with ATC.When the aircraft was at 10;000; a further descent to 7;000 feet was approved by ATC and speeds in excess of 250 knots were directed by the Captain. When the cabin altitude was below 10;000 feet; all crew members removed oxygen masks and prepared for the approach. Landing was uneventful but the aircraft started pressurizing on the ground during taxi. First Officer manually depressurized and aircraft was parked and engines shut down without incident.Preliminary reports from Maintenance indicate the ducting from the vent extraction fan ruptured.


Synopsis: A300 flight crew reported returning to departure airport due to pressurization problems; later traced to a vent extraction fan ducting.