500' FIGURE 10. OVER OTHER THAN CONGESTED AREAS
c. In the case of open water and sparsely populated areas, § 91.119(c) further requires that aircraft operate not closer than 500 feet from persons, vessels, vehicles or structures. (See figure 11.)
500.
500' 500 FIGURE 11. OVER WATER AND SPARSELY POPULATED AREAS Page 8
8. APPROACH AND LANDING. When a landing site is being considered, consideration should be given to the site's suitability. For example, city streets and highways, small fields occupied by large gatherings of people not associated with the ballooning activity, and tields containing obstructions (such as power lines) may be inappropriate landing sites in certain instances. When considering the prevailing surface wind, aeronauts should make certain that adequate ingress/egress is available with respect to the above obstructions. Before descending below the cruise altitude, aeronauts should keep in mind the need to fly a reasonable descent path to the proposed landing site. The approach to the site may be accomplished in several ways. In a no wind situation, simply settling vertically may suffice; however, when winds are involved, an approach path involving track and descent will be required.
a. Two methods may be used to accomplish an approach path involving track and descent.
(1) A stairstep approach involving varying descent rates may be used. It is important to avoid any long level flight segments below minimum safe altitudes. (See figure 12.) This procedure may be used sometimes may be quite shallow, it is important to avoid level flight segments below minimum safe altitudes.
Such level flight periods could lead observers to believe that the pilot has discontinued the approach and established level cruising flight at less than a minimum safe altitude.
FIGURE 12. STAIRSTEP APPROACH
(2) Another approach procedure is to establish a descent path of approximately 3°, consistent with groundspeed, trading off altitude for distance traveled. However, in some cases, a steeper or shallower descent path may be more desirable. A shallow glidepath of approximately 3 degrees has been established as a general standard by the aviation industry for descents over congested areas. For hot air balloons, this general standard may need to be modified, but it is a good basic guideline. Achievement of a 3° glidepath at a forward groundspeed of 5 knots requires a descent rate of 26 to 27 fpm. A comparison of descent rates versus groundspeed is provided in figure 13. For values not depicted, a straight-line variation may be employed to calculate the descent rate required for a 3° glidepath.
GROUNDSPEED (KNOTS) co 5 7 9 11 13 _15
37.2 26.6 15.9 6.3 DESCENT RATE (FPM) 47.8 3 DEGREE GLIDEPATH,
58.6
69.2 FIGURE 13. DESCENT RATES
b. To successfully accomplish a desired descent path, pilots may elect to use an aim point reference.
The aim point is a reference on the ground which, for any given rate of descent, remains constant in the pilot's field of vision during the descent and landing. It is also the point at which the basket will touch down. The aim point will be closer to the basket railing during steeper approaches and closer to the skirt during shallower approaches. However, if the rate of descent, windspeed, and wind direction all remain constant during the approach, the aim point will remain constant in the pilot's field of vision. If the rate of descent, windspeed, or wind direction change, the aim point will start to move. This indicates that the projected touchdown point also is changing. As the changing conditions and the approach stabilize, a new ground location will become constant in the pilot's field of vision, defining the new touchdown point. The new aim point will remain stationary and appear to grow larger as the balloon continues the approach. The challenge for the pilot is to control the rate of descent so that the desired landing point does remain constant in the field of vision throughout the approach. As the pilot looks down the descent path, if an obstacle blocks the pilot's view of the proposed landing site, the descent path is too low to clear the obstacle. Alternately, if the pilot looks down the descent path and no obstacles block the pilot's view of the aim point, the descent path is above obstacles. Use of the aim point reference can provide the pilot advance warning of impending problems.
9. WIND COMPONENTS.
a. Normally, during level flight in a balloon, the occupants in the basket feel no wind at all. This is because the balloon has joined an air mass and is moving in the same direction and at the same speed as the air mass (figure 14).
5 KNOTS
LEVEL FLIGHT 5 KNOTS FIGURE 14. WIND SAME DIRECTION AND SPEED
b. Windshears. As the balloon climbs or descends, it may transit through wind shears (generally 3 to 7 knots in differential velocity) as the balloon transits from one air mass to another. As the balloon passes through the shear and it transits into a wind which is blowing from another direction or at another speed, the occupants in the basket will momentarily feel a breeze as the envelope 'drags" the basket through the lower air mass.
(1) As the balloon climbs through the shear depicted in figure 15, the occupants in the basket will feel a momentary breeze. This is because the envelope is in a different air mass, moving to the left, and dragging the basket through the lower air mass. Once the basket climbs into the same higher air mass, the occupants will cease feeling a breeze and the balloon will change direction, moving in the direction from which the breeze is coming. In other words, the occupants felt a breeze coming from the left and the balloon can be expected to change direction to the left because the upper air mass is moving to the Page 11
ASCENDING WIND WIND FIGURE 15. ASCENDING THROUGH WINDSHEAR
(2) In a descent, the opposite situation occurs. As the balloon descends through the shear depicted in figure 16, the occupants in the basket will feel a momentary breeze from another direction. This is because the envelope is moving to the left, dragging the basket through the lower air mass. Once the envelope descends into the lower air mass, the balloon will begin to travel in the new direction and the occupants will cease feeling a breeze. Once the envelope fully enters the lower air mass, it will change direction, moving in the opposite direction from which the breeze was felt. In other words, the occupants having felt a breeze coming from the left, the balloon can be expected to change direction to the right because the lower air mass is moving to the right.
DESCENDING WIND WIND FIGURE 16. DESCENDING THROUGH WINDSHEAR Page 12
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