Date: 201911
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Light: Night
Aircraft: B757-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Illness / Injury
Detector: Automation Aircraft Other Automation
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Physical Injury / Incapacitation
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We were climbing out to the north and the First Officer was the pilot flying. Passing through about FL280 we received the master warning horn and light and the CABIN PRESS EICAS warning. I reached over and returned the left pack to auto (it had been turned off due to dual pack noise); we donned oxygen and established communications and we ran the QRC procedure. I got a clearance to stop the climb at FL290. I saw that the pressure gage read somewhere between 10;000 feet and 15;000 feet cabin pressure. I requested a descent; initially to FL250 and then to 10;000 feet. I did not feel that a max rate decent was warranted due to traffic and weather; so we descended safely but expeditiously. The First Officer advised me that he felt some symptoms of hypoxia. During the descent the cabin altitude got below 10;000 feet and the warning horn stopped. I did not know what the problem was since there were no other EICAS or system failure lights. It could have been descending that fixed the problem; or it could have been returning to dual pack operations; or it could have been both. Since I didn't know what problem I had; and since my First Officer had indicated that he had been hypoxic; I elected to advise ATC and return to ZZZ. Since I was asymptomatic I flew the approach and landing and there were no further abnormalities. We returned the plane to Maintenance.


Second narrative: I was the First Officer and the pilot flying; we were on climb out through FL280 heading northwest; we had the left pack off for cockpit noise reduction with the right pack in the auto position. We received a CABIN ALTITUDE EICAS message and lights; and the warning horn and light. We initially asked ATC to stop the climb at FL290 and were approved to do so. We donned oxygen and established crew communication; ran the QRC; and asked ATC for a descent initially to FL250; then to 10;000 feet. At some point during the event I recognized the onset of hypoxia symptoms from the momentary delay in donning oxygen and informed the Captain. He elected to divert back to ZZZ at that point. The cabin altitude indicated on the gauge descended through some combination of turning the left pack back on as part of the QRC procedure and the aircraft descent to lower altitude; and eventually the cabin altitude EICAS message and lights went out. Since the cabin pressure altitude was descending (not uncontrollable) we did not do a maximum performance descent; but rather an idle flight level change descent. The Captain spoke with ATC; we picked our way through multiple cells on the weather radar and set up the FMC for an ILS to XXR and briefed the approach. Though the hypoxia symptoms quickly dissipated; I elected to remain on oxygen for a prolonged time based upon my military training. Since I had been symptomatic and the Captain had no complaints of hypoxia; I recommended that he assume the pilot flying role for the approach and that I back him up as pilot monitoring. He flew the approach uneventfully and we returned the aircraft to Maintenance.


Synopsis: B757 flight crew reported a loss of pressurization during climb resulting in a return to departure airport.