Which of the following is true about the base of the ceiling when the base is 1,800 feet MSL and terrain is 1,295 feet MSL?

• A. 505 feet AGL
• B. 1,295 feet AGL
• C. 1,800 feet AGL
• D. 2,000 feet AGL

Answer: (A)

Cloud base above the ground is found by converting from MSL: subtract the terrain elevation from the cloud base altitude. So, 1,800 feet MSL minus 1,295 feet MSL equals 505 feet. That means the ceiling base is 505 feet above ground (505 feet AGL). This is the measurement pilots use for immediate flying conditions relative to the terrain, which is why 505 feet AGL is the correct interpretation. The other numbers would correspond to either the terrain elevation itself or the cloud base in MSL, not the altitude above ground.