According to the dash-1/NATOPS, where should the ISS switch be positioned when two crewmembers are on board the T-6 aircraft?

The correct positioning of the ISS switch when two crewmembers are aboard the T-6 aircraft is "BOTH." This setting is crucial for ensuring that both pilots have access to the oxygen supply and can benefit from the integrated supply system. In a dual-crew environment, the "BOTH" option ensures that both crew members receive adequate oxygen during critical phases of flight, such as takeoff, maneuvers, or emergency situations, where maintaining a clear mental state is essential for safety.

By selecting "BOTH," the flight crew enhances safety and operational readiness, as it allows for more effective communication and coordination. The other options would not provide the same level of oxygen support for both individuals, potentially compromising situational awareness and overall mission effectiveness. Therefore, using the "BOTH" setting is a recommended practice per the dash-1/NATOPS operating procedures.