FAA Sport Pilot Airplane (SPA)Airspace and NavigationMedium
A pilot studying a sectional chart sees an obstruction symbol near the route labeled '3255' above and '(824)' below in parentheses. What do these two numbers represent?
- ABoth numbers show the same height, once in feet and once in meters
- B3255 is the terrain elevation of the quadrangle; 824 is the Maximum Elevation Figure
- C3255 is the obstruction's height above mean sea level; 824 is its height above ground level
- D3255 is the obstruction's height above ground level; 824 is its height above mean sea level
Show answer & explanationAnswer & explanation
Correct answer: C. 3255 is the obstruction's height above mean sea level; 824 is its height above ground level
On sectional charts, obstruction symbols show the top elevation above mean sea level (MSL) as the larger, unparenthesized number, and the height above ground level (AGL) as the smaller number in parentheses. Here the obstruction's top is 3,255 feet MSL, and it stands 824 feet above the surrounding terrain.
Why the other options are wrong
- A. The numbers represent different reference points (MSL vs. AGL), not unit conversions.
- B. MEF is a separate bold number for an entire quadrangle, not tied to a single obstruction symbol.
- D. This reverses the correct order; MSL is the larger unparenthesized number.
Obstruction Symbol Elevation
Sectional chart obstruction symbols display height above mean sea level (top number) and height above ground level (parenthesized number).
- Top number = MSL height of the obstruction's tip
- Parenthesized number = AGL height of the obstruction
- Filled symbols typically indicate lighted obstructions
- Group symbols represent clusters of obstructions in close proximity
Memory trick: 'Top hat is Sea level, Bottom bracket is the Ground' (MSL on top, AGL in parentheses)