Whidbey Island Class C, NAS Whidbey and R-6701 · Seattle Sectional, 3 Sep 2026 – 29 Oct 2026 · Seattle.pdf (FAA current sectional, not redistributed), p. 1 · Not for navigation
Refer to the current Seattle sectional excerpt near Arlington, Washington. An obstruction there is charted as "882 (315)." What is its top elevation above mean sea level (MSL)?
Why: The unparenthesized number in a charted obstruction's data block is its top elevation above mean sea level: 882 feet MSL here. The parenthesized 315 is a separate reading — the obstruction's height above ground level (AGL).
315 is the obstruction's AGL height (the parenthesized figure), not its MSL elevation.
Invents an addition (882 + 315) that isn't how the chart presents the data — the MSL elevation is printed directly as 882, with no arithmetic needed.
UA.II.B.K7 · Source: Seattle.pdf, current edition sectional chart excerpt (gitignored full-resolution source; not redistributed — see sources/README.md) · Reviewed 2026-10-22