Narrative:

We experienced a very loud noise at FL400. It sounded like an alarm at first or high pitch squealing sound. After a few minutes the passengers had said they detected an odor that they thought was electrical and hydraulic in nature. At that time we started to turn around and divert the aircraft. Weather was 2;600 broken; 12 degrees C; 29.78; and winds of 360 at 17 knots. The loud sound in the aircraft did subside some in the descent and then returned; but not as loud. Also; the smell did change some as reported by the passengers. Once we were in the vicinity of [the airport] I actually did start to smell the odor as well. It reminded me of smells associated with both electrical and failed pacs. We requested the ILS xy; but were able to get a visual approach about 7 miles from the airport. The landing was approximately [30 minutes later]. We parked the aircraft; shut down; got passengers out and away from aircraft and then met with fire department and evaluated aircraft.

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Original NASA ASRS Text

Title: Flight Crew of CE-750 reported detecting smoke in cabin and diverted.

Narrative: We experienced a very loud noise at FL400. It sounded like an alarm at first or high pitch squealing sound. After a few minutes the passengers had said they detected an odor that they thought was electrical and hydraulic in nature. At that time we started to turn around and divert the aircraft. Weather was 2;600 Broken; 12 degrees C; 29.78; and winds of 360 at 17 knots. The loud sound in the aircraft did subside some in the descent and then returned; but not as loud. Also; the smell did change some as reported by the passengers. Once we were in the vicinity of [the airport] I actually did start to smell the odor as well. It reminded me of smells associated with both electrical and failed PACs. We requested the ILS XY; but were able to get a visual approach about 7 miles from the airport. The landing was approximately [30 minutes later]. We parked the aircraft; shut down; got passengers out and away from aircraft and then met with fire department and evaluated aircraft.

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.