A journey through 14 CFR 1.2 Abbreviations and Symbols
In the wonderful nerdy world of aviation, we pilots like to measure everything—speed, altitude, temperature, our coffee intake before takeoff. You name it, we measure it. But when it comes to altitude, we don’t just guess based on a gut feeling and cloud proximity. No, we measure it from a universal starting point known as Mean Sea Level (MSL) .
Soo… What the Heck is MSL?
Think of MSL as the planet’s “elevation zero.” It’s the average level of the ocean over time—like, 19 years of ocean mood swings. High tide, low tide, hurricane tantrums, it all gets averaged out to one consistent baseline. And because using the actual ocean at any given moment would be chaos—especially if you’re flying over Kansas—we use this steady average to keep aviation sane and safe.
Why do Pilots use MSL?
Flying at 10,000 ft MSL means you’re 10,000 ft above sea level—not 10,000 ft above Aunt Judy’s backyard. That’s a crucial distinction. Because the ground? Well, it’s shifty. Sometimes it’s a beach, sometimes it’s the Rocky Mountains, and sometimes it’s just stubbornly high cornfields in Iowa.
MSL provides pilots a common language for altitude, no matter what’s going on down below. Charts, airspace rules, flight levels, they all use MSL. And since everyone’s aircraft altimeters display altitude in MSL, it hopefully keeps aircraft from playing accidental bumper cars in the sky.
Crock’s Final Thoughts
So, MSL might sound like something Poseidon dreamed up within a board room, but it’s the unsung hero of safe flight. It gives us a fixed altitude reference in a world where the ground can’t make up its mind.
Because in aviation, mean isn’t about attitude. It’s just about not bumping into the earth.
Crock’s Thoughts 