Narrative:

We started the day normally. We needed to reposition the airplane to an airport about 30 miles away. On such a short trip we left our acus (air conditioning units) running on the APU (auxiliary power unit) which is SOP (standard operating procedures). This flight was normal and we started to prepare the airplane for our passengers. After we loaded up our passengers we proceeded to the runway for departure. Still every system had checked out normally. We had our acus running on our APU for takeoff since we were a little heavy for the runway but well within the limits. We did the noise abatement departure procedure on departure; bringing the power back at the end of the runway and climbing out at V2 with flaps at 15 degrees until the shoreline at about 3000'. The controller began to give us headings and altitudes towards our flight plan route. At around 5000' we proceeded to do our bleed air transition from the APU to the engines. I brought the power back and authorized the transition as per our sops. However; upon transitioning; the right acu did fail but the left acu appeared to operate normally. I had my copilot check the checklist and see if he could fix the problem. I was accepting new headings and altitudes with directions to hurry through 13;000' and going up to 17;000'. My copilot was headed down the checklist when he notice that the cabin pressure was nearing 10;000' and we were about to drop the passenger oxygen masks. I tried to buy us some time by leveling off at about 15;700' and by applying emergency pressurization. It was too late; the masks had dropped and about that time we started to get a toxic smoke in the cockpit. We put on our masks and declared an emergency and headed for our original airport. On the descent I figured the smoke was being caused by the emergency pressurization so I turned it off. To clear the smoke I selected emergency depressurization and ram air. We proceeded to land without further event at our home base airport. We had our passengers disembark and worked with dispatch to get them another airplane. In retrospect we had three issues. The first was the right acu over pressurized and failed. Also the second acu apparently did not work but had no fail indication. And third the emergency pressurization air was contaminated and creating smoke in the cockpit. Maintenance found the left acu failed due to a circuit breaker. The right acu sov (shut-off valve) was swapped but seemed to be working normally; it probably over pressurized due to the lack of help on the left acu. The emergency pressurization takes raw uncooled bleed air and applies it to the ducts which may have had traces of oil or other debris that started to produce toxic smoke. What did I learn from all this? Well the accident chain was forming and fortunately we stopped the chain but it had built up a couple of links. When we transition the bleed air from the APU to the engines and had a failure I should have stopped climbing immediately and evaluated the pressurization system. I had assumed that the other acu was working and losing only one acu is usually not a big problem. The next lesson was with emergency pressurization. Emergency pressurization is rarely used and the debris that ends up in these ducts may become toxic. Emergency pressurization should only be used to get the airplane down from altitude following a depressurization at altitude; and should only be used for a short duration.

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Original NASA ASRS Text

Title: A CL600 air conditioning unit failed after takeoff; then the opposite bleed air valve closed resulting in loss of pressurization at 15;000'. During the turn back; the cabin filled with smoke when the emergency pressurization was enabled.

Narrative: We started the day normally. We needed to reposition the airplane to an airport about 30 miles away. On such a short trip we left our ACUs (Air Conditioning Units) running on the APU (Auxiliary Power Unit) which is SOP (Standard Operating Procedures). This flight was normal and we started to prepare the airplane for our passengers. After we loaded up our passengers we proceeded to the runway for departure. Still every system had checked out normally. We had our ACUs running on our APU for takeoff since we were a little heavy for the runway but well within the limits. We did the noise abatement departure procedure on departure; bringing the power back at the end of the runway and climbing out at V2 with flaps at 15 degrees until the shoreline at about 3000'. The Controller began to give us headings and altitudes towards our flight plan route. At around 5000' we proceeded to do our bleed air transition from the APU to the Engines. I brought the power back and authorized the transition as per our SOPs. However; upon transitioning; the right ACU did fail but the left ACU appeared to operate normally. I had my copilot check the checklist and see if he could fix the problem. I was accepting new headings and altitudes with directions to hurry through 13;000' and going up to 17;000'. My copilot was headed down the checklist when he notice that the cabin pressure was nearing 10;000' and we were about to drop the passenger oxygen masks. I tried to buy us some time by leveling off at about 15;700' and by applying emergency pressurization. It was too late; the masks had dropped and about that time we started to get a toxic smoke in the cockpit. We put on our masks and declared an emergency and headed for our original airport. On the descent I figured the smoke was being caused by the Emergency Pressurization so I turned it off. To clear the smoke I selected Emergency Depressurization and Ram Air. We proceeded to land without further event at our home base airport. We had our passengers disembark and worked with dispatch to get them another airplane. In retrospect we had three issues. The first was the right ACU over pressurized and failed. Also the second ACU apparently did not work but had no fail indication. And third the Emergency Pressurization air was contaminated and creating smoke in the cockpit. Maintenance found the left ACU failed due to a circuit breaker. The right ACU SOV (Shut-Off Valve) was swapped but seemed to be working normally; it probably over pressurized due to the lack of help on the left ACU. The Emergency Pressurization takes raw uncooled bleed air and applies it to the ducts which may have had traces of oil or other debris that started to produce toxic smoke. What did I learn from all this? Well the accident chain was forming and fortunately we stopped the chain but it had built up a couple of links. When we transition the bleed air from the APU to the engines and had a failure I should have stopped climbing immediately and evaluated the pressurization system. I had assumed that the other ACU was working and losing only one ACU is usually not a big problem. The next lesson was with Emergency Pressurization. Emergency Pressurization is rarely used and the debris that ends up in these ducts may become toxic. Emergency Pressurization should only be used to get the airplane down from altitude following a depressurization at altitude; and should only be used for a short duration.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.