I'm going to try something new. A couple of times each week I'm going to make a post reviewing long forgotten or rarely discussed regulations. Some of the regulations I'll review will be rather trivial , some significant, and some will be a clarification of widely misinterpreted regulations. I understand that the human brain only opens its intake filter for content it deems important and useful, so I'll explain the reason behind each regulation I review. If I don't know the reason, I'll give you my best educated guess. Because regulations are important to pilots for several reasons (enforcement action, safety, operational requirements), I think this new column will be helpful to readers. I'll also occasionally throw in guidance topics from the Aeronautical Information Manual (AIM) and FAA Advisory Circulars (AC). It will be a good review for me, too!
Let's get started with the first review.
Topic
Advisory Circular 91-36D, VFR Flight Near Noise-Sensitive Areas
"This Advisory Circular (AC) encourages pilots making VFR flights near noise-sensitive areas to fly at altitudes higher than the minimum permitted by regulation and on flight paths that will reduce aircraft noise in such areas." (See AC document for complete details.)
Interpretation
VFR aircraft are requested to fly at least 2,000 feet above ground level (AGL) over designated national wildlife refuge areas and other noise-sensitive areas. We know where these areas are located by finding them on VFR navigational charts (TAC, SAC, or WAC). We can compute the minimum requested mean sea level (MSL) altitude which will yield 2,000 feet AGL by decoding the terrain elevation color shown on the map (refer to the map legend for color-to-number translation) and adding 2,000. Add another five hundred feet to give yourself a margin for altitude drift and nonuniform terrain elevation. For an easier method, add 2,000 to the Maximum Elevation Figure (MEF) shown on the chart, plus a five hundred foot margin. This method won't work in extremely rugged terrain or where there are unusually high obstacles around (i.e. a tethered weather balloon) because the MEF might apply to an area miles away from the noise-sensitive area and might put you much higher than 2,000-3,000 feet AGL.
Explanation
The government wants to limit noise pollution in these areas. Airplanes are noisy, especially when they're less than 2,000 feet away. Think about it... Ground vehicles are restricted in these areas, and air vehicles are too. That's why they call these areas refuges. The idea here is to protect these nature areas from the nuisance of aircraft engine noise so that people and animals can enjoy them.
