Narrative:

We taxied out for takeoff on our trip back to our origin. In view of the hot and humid environment; we taxied to the runway with the bleed air switches in the middle position which activates all bleed air systems except the pressurization system. As previously discussed as an acceptable procedure with beechcraft we planned to apply bleed air to pressurize the cabin immediately after takeoff to maximize takeoff performance. After takeoff; tower instructed us to turn left to a heading of 150 degrees which we complied. Leveling on the 150 degree heading and at approximately 600 ft AGL; the co-pilot turned on the left bleed air which immediately began to pressurize the cabin. Within seconds; two of our passengers complained they smelled something 'burning' and saw a hazy environment in the cabin. While we speculated the problem was directly related to activation of the bleed air system in the hot and humid environment in which we were operating; we were not sure if we had an electrical/smoke problem with the aircraft and; thus returned to the airport for maintenance evaluation. Back on the ground; we contacted our maintenance coordinator and explained the situation. He required us to perform several checks on the ground with the engines running and the same electrically systems activated first excluding the bleed air system and then including each bleed air system one at a time. About 45 minutes later with engines still running at the maintenance pad; we called maintenance back to report the results of the ground run-up tests of the electrical system. There were no abnormalities or abnormal smells. We subsequently tested each bleed air system and eventually both bleed air systems at the same time without any abnormalities. At this point; maintenance instructed us to test fly the aircraft without passengers. We contacted ground control and requested to fly to an area 5 miles southeast of the airport. Ground control approved the request and instructed us to taxi for take-off. The test flight; with all required systems activated including the bleed air systems; occurred without any problems or issues. Back on the ground we again spoke to maintenance and reported our successful test flight. Maintenance released us to reinitiate our return flight back to [intended destination] with our passengers. The flight back was uneventful without incidence.in the future; we will notify the passengers that they may smell something after takeoff or see a puff of haze/smoke if we should use the same procedure of delaying application of the bleed air systems for maximum takeoff performance.

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Original NASA ASRS Text

Title: On a hot; humid day; a BE-20 crew taxied and departed with the engine bleeds supplying air conditioning only. After pressurizing; fumes and a puff of smoke prompted a return to land. Troubleshooting and a test flight found no aircraft problems.

Narrative: We taxied out for takeoff on our trip back to our origin. In view of the hot and humid environment; we taxied to the runway with the bleed air switches in the middle position which activates all bleed air systems except the pressurization system. As previously discussed as an acceptable procedure with Beechcraft we planned to apply bleed air to pressurize the cabin immediately after takeoff to maximize takeoff performance. After takeoff; tower instructed us to turn left to a heading of 150 degrees which we complied. Leveling on the 150 degree heading and at approximately 600 FT AGL; the co-pilot turned on the left bleed air which immediately began to pressurize the cabin. Within seconds; two of our passengers complained they smelled something 'burning' and saw a hazy environment in the cabin. While we speculated the problem was directly related to activation of the bleed air system in the hot and humid environment in which we were operating; we were not sure if we had an electrical/smoke problem with the aircraft and; thus returned to the airport for maintenance evaluation. Back on the ground; we contacted our Maintenance Coordinator and explained the situation. He required us to perform several checks on the ground with the engines running and the same electrically systems activated first excluding the bleed air system and then including each bleed air system one at a time. About 45 minutes later with engines still running at the maintenance pad; we called Maintenance back to report the results of the ground run-up tests of the electrical system. There were no abnormalities or abnormal smells. We subsequently tested each bleed air system and eventually both bleed air systems at the same time without any abnormalities. At this point; Maintenance instructed us to test fly the aircraft without passengers. We contacted Ground Control and requested to fly to an area 5 miles southeast of the airport. Ground Control approved the request and instructed us to taxi for take-off. The test flight; with all required systems activated including the bleed air systems; occurred without any problems or issues. Back on the ground we again spoke to Maintenance and reported our successful test flight. Maintenance released us to reinitiate our return flight back to [intended destination] with our passengers. The flight back was uneventful without incidence.In the future; we will notify the passengers that they may smell something after takeoff or see a puff of haze/smoke if we should use the same procedure of delaying application of the bleed air systems for maximum takeoff performance.

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.