What is the degree of error for lines of bearing on the R-21 system unless otherwise stated?

• A. +/- 1 degree
• B. +/- 4 degrees
• C. +/- 10 degrees
• D. +/- 20 degrees

Answer: (B)

Lines of bearing have a finite angular accuracy. For the R-21 system, unless another value is stated, the bearing is accurate to plus or minus four degrees. That means the true line could be four degrees either side of the indicated bearing. This default tolerance is what you rely on when crossing lines to fix a position, and it also shows how the fix accuracy degrades with range—the farther you are, the larger the potential lateral error from a four-degree bearing uncertainty. For example, at 10 nautical miles, four degrees can translate to about 0.7 nautical miles of offset; at 30 nautical miles, around 2.1 nautical miles. The other options don’t reflect the typical default angular tolerance for this system.