AGL, MSL, and the Altitude Conversion
Put terrain, obstacles, airspace, and aircraft altitude into the same reference before comparing them.
YOU WILL BE ABLE TO
- 01Identify the rule, source, or principle behind this idea: AGL is height above the surface directly below; MSL is elevation above mean sea level.
- 02Explain the operational effect of this idea: Sectional airspace and obstacle values commonly use MSL, while Part 107 altitude limits commonly use AGL.
- 03Apply the lesson to a new mission and defend a go, modify, or no-go decision.
01 / MISSION
Begin with the operating problem.
A launch at 1,850 feet MSL plans to climb 300 feet AGL beneath a 2,000-foot MSL shelf.
02 / CORE BRIEF
What the remote pilot needs to know.
AGL is height above the surface directly below; MSL is elevation above mean sea level.
Sectional airspace and obstacle values commonly use MSL, while Part 107 altitude limits commonly use AGL.
A simple planning conversion is launch elevation MSL plus planned height AGL, adjusted when terrain changes.
03 / PILOT DECISION
Make the call.
The planned aircraft altitude would be about 2,150 feet MSL, so the route enters the shelf and must be replanned or authorized.
04 / FIELD CHECK
Put it into the flight plan.
Write both altitude references beside every important vertical limit.
05 / KNOWLEDGE CHECK
Why can 300 feet AGL still cross a shelf whose floor sounds much higher?
Reveal the debrief
Because the shelf is expressed in MSL and terrain elevation must be added to the aircraft's AGL height.
RELATED FAA REFERENCES
Verify before you fly.
Educational summary only. Current regulation, FAA approval conditions, manufacturer instructions, and site-specific facts control the operation.