Date: 201502
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: Citation I/SP (C501)
Operator: Air Taxi
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization Control System
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Time Pressure; Workload
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC complied w / Automation / Advisory; Flight Crew Returned To Departure Airport
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During a routine climb enroute; going through FL320; we heard a loud thump from the back of the airplane. We quickly noticed a change in cabin pressure. We donned our oxygen masks. I immediately slowed the aircraft climb rate from 2000 FPM; to near level. The FO; and I determined very quickly the cabin pressurization was not controllable and cabin rate of climb exceeded 4000 Fpm climb rate. I instructed the FO to request a lower altitude; and that we needed to return to the departure airport.I initiated an expedited descent prior to receiving an ATC clearance.


Second narrative: Climbing through FL320 to our assigned altitude of FL410; both pilots noted a pop sound.  I felt a cabin pressure change in my ears and heard the sound of air escaping.  Both pilots checked the cabin vertical speed indicator and noted a climb of approximately 3000 FPM.  We donned oxygen masks and the pilot flying began to level from the climb.  I stated we had lost pressurization and needed a lower altitude.  The pilot flying began a descent.  I informed Center we were initiating a descent and requested a return to our departure airport.  The Controller cleared us to FL280 and asked for fuel remaining and souls on board.  The 10;000 feet cabin altitude light illuminated as the cabin continued to climb rapidly. We attempted to make adjustments to the pressurization system with no effect. As we descended; I made a second request for a return to Airport ZZZ. The Controller cleared us to FL210 and direct. Both pilots noted a sound in the cabin as the passenger masks deployed. As we descended and turned toward our destination; the cabin reached the aircraft altitude and began to descend with the aircraft. When we activated emergency pressurization; there was no effect since the cabin was already descending with the aircraft. ATC issued a further clearance for descent and below 10;000ft we removed the masks. I informed ATC the emergency was complete and priority handling was not required. The Controller cleared us direct for an ILS 28R.  We conducted a normal approach to landing.  Under the emergency circumstances of a rapid decompression; it was necessary to stop the climb and begin a descent as soon as possible.


Synopsis: A C501 climbing through FL320 rapidly lost pressurization with a 'pop' sound; oxygen masks donned and the flight safely returned to the departure airport.