10. EXCEPTIONS. The previous are rules-of-thumb. Although they are generally accurate, there can be exceptions. For example, if a balloon was descending as depicted in figure 17, the pilot would momentarily feel a breeze from another direction. The rule-of-thumb would lead the pilot to expect the balloon to move to the right but, in this case, the balloon would stop moving when the envelope stabilized in the lower air mass.
DESCENDING WIND CALM FIGURE 17. DESCENDING INTO CALM AIR
a. If a balloon were descending in the situation depicted in figure 18, the pilot would momentarily feel a breeze from another direction. The rule-of-thumb would lead the pilot to expect the balloon to move to the right. However, in this case, the balloon would continue to move to the left, but at a slower speed once the envelope fully stabilized in the lower air mass.
DESCENDING WIND 10 KTS WIND 3 KTS FIGURE 18. DESCENDING INTO DIFFERENT WIND VELOCITY Page 13
b. If pilots apply the above rules-of-thumb during climbs and descents and pay attention to gentle breezes, valuable information can be derived. The statement, "the balloon encountered an unexpected wind gust that pushed it into an obstruction before a pilot could react," is an unfortunate corollary to an accident.
Application of general rules-of-thumb may provide advance warning and assist pilots to recognize and correct impending problems.
11. ADVISORY MATERIAL. The procedures and techniques discussed in this AC are advisory in nature.
They are general guidance and should not be construed as required operating practices. This AC also contains numerous excerpts from, and references to, compliance with part 91. The regulations themselves are not advisory, and compliance is required. Applicable operating limitations and procedures contained in manufacturer's FAA-approved flight manuals, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry, take precedence over the information contained in this AC.
Millan : Mhito William J. White Deputy Director, Flight Standards Service Page 14
U.S. Department of TransporTation Federal Aviation Administration 800 Independence Ave., S.W.
Washington, D.C. 20591 Official Business Penalty for Private Use $300