Learjet 55
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 50; Flight Crew Total 8600; Flight Crew Type 4500
Distraction; Time Pressure; Troubleshooting; Workload
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Other / Unknown
Aircraft Equipment Problem Dissipated; Flight Crew Became Reoriented; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Aircraft; Human Factors
Level at FL400 for twenty minutes going west bound we lost cabin pressurization. We heard a loud noise in the cabin area and almost at the same time I felt something in my ears; I looked at the cabin controller and noticed an excessively fast rising cabin. I immediately started the emergency descent and told my copilot to put on his mask and notify center of our emergency. He changed the transponder to 7700 and communicated with Center. We completed the emergency descent checklist and got down to a safe altitude within three minutes making sure our passenger was safe and aware of our situation. On the way down the cabin never seemed to go above 10;000 feet so I was able to communicate with our passenger quite easily. After stabilizing the plane into the descent; and completing the checklist I looked back at our cabin and noticed that the cabin O2 mask did not drop after I had turn knob.Once down to a safe altitude we were able to trouble shoot the cabin pressurization and found that we could stabilize it at approximately 6;700 feet while cruising at 17;000 feet. With VFR weather and enough fuel we continued the flight to our filed destination without further problems.
Learjet 55 flight crew reported losing cabin pressurization at FL400; but because of a rapid crew response the cabin did not exceed 10;000 feet. When finally stabilized the cabin maintained 6;700 feet at 17;000 foot cruise. The passenger O2 masks did not deploy even though manually activated.