Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer
Flight Crew Last 90 Days 50; Flight Crew Total 14800; Flight Crew Type 254
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action; General Maintenance Action
Aircraft
In cruise at FL180; the temperature in the cabin became very cold suddenly. I increased the selected temperature with the auto temperature control rheostat; and the temperature did not change after several minutes. I then selected manual hot for about three seconds. The temperature coming out of my side duct began to warm. I left the temperature controller in auto after having moved the mix valve to a warmer selection in manual; and monitored the temperature. Several minutes later; the temperature coming out of the duct suddenly rose dramatically; and I could smell a burning smell. I immediately went to manual cold and tried to decrease the temperature; but concurrently the passengers in the back alerted me to smoke in the cabin. I called the Center controller and told him I needed lower immediately; and he cleared me to 11;000 feet. The temperature continued to come out hot; so I took the bleed air switches to off; and the cabin began to rapidly climb as I was in a rapid descent from FL180 to 11;000 feet. Once the bleed valves were turned off; there was no more smoke; and no more heat coming from the air ducts. At 11;000 feet; I turned the bleed valves back on one at a time; and cold air came out of the ducts. I was able to control the cabin in this configuration; and we flew the rest of the way with cold air coming from the air ducts. After landing; I passed the information on to our mechanics; and they are investigating the auto temperature control box for the ACM (Air Cycle Machine) as the culprit. Center asked if we were declaring an emergency; and we told them we had it under control with the descent to 11;000 feet. They asked if we needed any further assistance; and we told them we did not.
MU-2 Captain experiences very cold conditioned air at FL180. Initial attempts to warm the air are unsuccessful until manual is selected; then the air becomes too hot producing smoke. Attempts to cool the air using manual control are unsuccessful initially; so the bleeds are turned off and the aircraft is descended to 11;000 feet. Flight continues to destination at 11;000 feet.