A rotor wing aircraft is based at 5,200 feet and flies at 1,200 feet AGL. Which statement about altitude is correct?

• A. Are flying in the space equivalent zone
• B. The pilot requires oxygen if the duration of the flight exceeds 30 minutes
• C. Oxygen is required for all passengers if the cabin is not pressurized
• D. The aircraft is flying at 6,400 MSL

Answer: (D)

Altitude is given as mean sea level (MSL), and AGL must be added to the field elevation to get MSL. The base is at 5,200 ft, and the aircraft is 1,200 ft above the ground, so 5,200 + 1,200 = 6,400 ft MSL. So the aircraft is at 6,400 feet MSL. Oxygen rules hinge on cabin or flight altitude in unpressurized aircraft; 6,400 ft MSL is well below the 12,000 ft threshold where supplemental oxygen becomes required, so statements about oxygen needs at this altitude aren’t applicable. The term about a “space equivalent zone” isn’t a standard altitude category, so the only statement that matches the actual altitude is that it’s flying at 6,400 feet MSL.