Environmental system smoke or odor: after the crew dons oxygen masks and selects Mic to OXY MASK, the next action is to isolate the cabin pressure source by selecting L ENG or R ENG.

Environmental system smoke or odor: after the crew dons oxygen masks and selects Mic to OXY MASK, the next action is to isolate the cabin pressure source by selecting L ENG or R ENG.

• A. Isolate the cabin pressure source by selecting L ENG or R ENG
• B. Increase cabin pressure
• C. Open outflow valve
• D. Turn off the environmental system

Answer: (A)

Isolating the bleed air source is the immediate action when there’s smoke or odor in the environmental system. After you’ve donned oxygen masks and set the mic to OXY MASK, the next step is to shut off the bleed air from the engine that's feeding the affected circuit. On the Beechjet 400A, you do this by selecting the engine to isolate. This stops contaminated bleed air from entering the cabin while you continue to breathe from the oxygen system and monitor the situation. Opening the outflow valve would vent cabin air and lower or destabilize pressure without addressing the source of contamination. Increasing cabin pressure or turning off the environmental system entirely aren’t as targeted or practical to quickly remove the contaminated air from the cabin. So isolating the specific engine bleed air is the best next action.

Isolating the bleed air source is the immediate action when there’s smoke or odor in the environmental system. After you’ve donned oxygen masks and set the mic to OXY MASK, the next step is to shut off the bleed air from the engine that's feeding the affected circuit. On the Beechjet 400A, you do this by selecting the engine to isolate. This stops contaminated bleed air from entering the cabin while you continue to breathe from the oxygen system and monitor the situation. Opening the outflow valve would vent cabin air and lower or destabilize pressure without addressing the source of contamination. Increasing cabin pressure or turning off the environmental system entirely aren’t as targeted or practical to quickly remove the contaminated air from the cabin. So isolating the specific engine bleed air is the best next action.