Narrative:

We departed on an empty reposition flight. The two legs that we previously flew in the aircraft were uneventful as was the departure. We had just started an intermediate descent from FL390 when and I smelled smoked; to clarify this was an intense acrid smell much like burning metal. Immediately we shut off the cockpit pack with the thought that this was perhaps the issue. The smell persisted and when we turned around to examine the cabin we noticed that there was hazy grey smoke filling it. Our next action was to turn on our oxygen masks and turn the cockpit pack on and turn the cabin pack off; at this time we also isolated the cabin electrical power by turning off the interior master switch. As the smoke was not dissipating we made the decision to execute an emergency descent. At this point we declared an emergency and decided the ZZZ airport was the best option considering that the smoke was not dissipating noticeably and that we could not positively identify its source. During the descent I handled the radios and manipulated the aircraft while the first officer ran the checklist for environmental smoke or odor in the cabin as well as that for electrical smell or odor - unknown source. At approximately 10;000 feet our focus became the approach and landing. We turned onto the localizer at approximately 20 miles. We regrouped and reconfigured for the landing which was uneventful. The airport rescue and firefighting (arff) met us on the ramp. They came aboard and inspected the aircraft for any sign of ongoing fire. By this time the smoke had dissipated. The aircraft was declared safe and the arff team left. We assisted maintenance in troubleshooting the problem; discussed acceptable options and secured the aircraft for the night. Further training on pack failures and regular inspection by maintenance of the packs to determine potential failures.

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Original NASA ASRS Text

Title: CE750 pilot experiences an intense acrid smell descending out of FL390 and the cockpit pack is turned off. The odor persists and the cabin pack is turned off and the cockpit pack turned on. Oxygen masks are donned; an emergency declared and the flight diverts to the nearest suitable airport.

Narrative: We departed on an empty reposition flight. The two legs that we previously flew in the aircraft were uneventful as was the departure. We had just started an intermediate descent from FL390 when and I smelled smoked; to clarify this was an intense acrid smell much like burning metal. Immediately we shut off the cockpit pack with the thought that this was perhaps the issue. The smell persisted and when we turned around to examine the cabin we noticed that there was hazy grey smoke filling it. Our next action was to turn on our oxygen masks and turn the cockpit pack on and turn the cabin pack off; at this time we also isolated the cabin electrical power by turning off the interior master switch. As the smoke was not dissipating we made the decision to execute an emergency descent. At this point we declared an emergency and decided the ZZZ airport was the best option considering that the smoke was not dissipating noticeably and that we could not positively identify its source. During the descent I handled the radios and manipulated the aircraft while the First Officer ran the checklist for environmental smoke or odor in the cabin as well as that for electrical smell or odor - unknown source. At approximately 10;000 feet our focus became the approach and landing. We turned onto the localizer at approximately 20 miles. We regrouped and reconfigured for the landing which was uneventful. The Airport Rescue and Firefighting (ARFF) met us on the ramp. They came aboard and inspected the aircraft for any sign of ongoing fire. By this time the smoke had dissipated. The aircraft was declared safe and the ARFF team left. We assisted maintenance in troubleshooting the problem; discussed acceptable options and secured the aircraft for the night. Further training on pack failures and regular inspection by maintenance of the packs to determine potential failures.

Data retrieved from NASA's ASRS site 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.