Date: 201309
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: BAe 125 Series 800
Operator: Air Taxi
Operating under: Part 135
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: Improperly Operated
Reporter organization: Air Taxi
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Distraction
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action; General Declared Emergency
Contributing factors: Procedure; Aircraft
Primary problem: Procedure

Narrative: While climbing through FL230; I noticed that the cabin rate needle abruptly increased to +2;000 FT per minute. Furthermore; the differential needle; initially at approximately 5 PSI; began trending toward zero; and the cabin altitude quickly started to climb from 4;000 FT. As ensured the dump valve was closed; the MAVs were open; and that the manual/automatic pressurization controls were set properly; I informed the pilot not flying of the situation. When the cabin altitude reached approximately 7;000 FT; I donned my oxygen mask; asked the pilot not flying to inform ATC we would need a lower altitude; and disengaged the autopilot. By the time the cabin altitude reached 8;500 FT; we had already begun our descent to 10;000 FT. The descent was conduced per the aircraft memory items; and the remainder of the Emergency Descent Checklist was finished by the pilot not flying after reaching 10;000 FT. The cabin altitude never exceeded 12;500 FT and the passenger oxygen masks were never deployed. During the event there were no other abnormal indications; and no abnormal sounds from the aircraft. At 10;000 FT we received a revised routing from ATC; and determined that we could still continue to our planned destination with the remaining fuel on board. We then contacted both Flight Tracking and Maintenance Control to inform them of the situation. After discussing the event as a team; the determination was made to continue the flight to our intended destination as long as the passengers also felt comfortable with the decision. The remainder of the flight was conducted without additional interruptions or complications; and we landed without further incident. I believe the crew reacted appropriately to the situation; and as trained/expected. Also; as long as we operate airplanes I do not believe that we can ever truly prevent mechanical failures from recurring. However; I do believe that there are a few ways we can lower the likelihood of this happening again; and I also believe that we can do more to mitigate some of the risk that the crew and passengers would be exposed to during a similar event.Later in the day; we learned from Maintenance that they could see that the pressurization hose leading to the water sock had become disconnected. The aircraft in question had been in the maintenance base the previous week for maintenance on the APU; and this was it's first flight to altitude since the maintenance was completed (our positioning flight was conducted at 5;000 FT). Maintenance said that to perform the APU work; they might have had to remove the hose in question; so I believe that the Maintenance Base could have potentially forgot to reconnect the hose; or failed to secure the hose clamp properly after finishing work on the APU. Additionally; I believe that Hawker Beechcraft (or our carrier if allowed by the FAA) could revise the Emergency and Abnormal section of the aircraft checklist. Having numbered tabs (instead of just writing out what the section contains on the tab itself) makes it slow and awkward to find the appropriate pages if you're in a hurry. Furthermore the checklist provides a bare minimum of information. Not only does it not expand or elaborate on the procedure; but it doesn't always direct you toward additional checklists when they're required. For example; the Engine Fire; Failure; or TR deployment during T/O checklist directs you to then complete the Engine Shutdown In Flight procedure. But the Engine Shutdown in Flight Procedure never directs you to then complete either the Engine Relight or the One Engine Inoperative Approach/Landing Checklist (one of which MUST be done). If these sections were streamlined; and if an expanded procedures section was added; I believe that safety during emergency/abnormal situations could be exponentially increased at our carrier.


Second narrative: After that; I talked with the passengers. They seemed to be fine and understood what had happened. We continued the flight to the destination at 10;000 FT then after regaining some pressurization (4;000 FT cabin altitude); we climbed to 12;000 FT altitude.


Synopsis: A BAE-125-850XP at FL230 crew declared an emergency; began a descent to 10;000 FT and completed the checklist as the cabin altitude climbed but later continued to the destination at 12;000 FT. Maintenance had not previously secured an air conditioning duct.