Operation Of Hot Air Balloons With Airborne HeatersOPERATION
OF HOT AIR BALLOONS WITH AIRBORNE HEATERS
SELECTION OF LAUNCH SITE.
The appropriateness of any launch site involves much more than its physical
size and absence of obstructions, even though these are important considerations.
Of equal or greater importance is the direction the balloon will track
following the launch. Any site selection made should include consideration
of local winds as determined by pibal, smoke, trees, or other physical
indications; forecast and reported winds aloft; and local phenomena peculiar
to the specific site (determined by personal knowledge or by consulting
with local balloonists).
Also, location of obstructions along the projected flight path and available suitable landing sites down range should be considered.
Once a launch site is selected and flight preparations have begun, any
situation that may adversely affect or change the planned flight (wind
shift, lowering clouds, or obscuring phenomena such as fog or smoke) should
be carefully considered. If the change or adverse situation is unacceptable,
the launch site should be moved to another location or the flight should
be canceled. The adage, "better to cancel and fly another day than to make
a mistake along the way," is a useful guideline.
TAKEOFF, DEPARTURE, AND CLIMB.
a. Before launching, care should be given to departure and climb considerations.
An obstacle assessment should be made. Where power lines or any other obstacles
are present, the pilot should have alternative courses of action available.
b. To compute the minimum distance between the launch point and obstacles
downwind, multiply the wind speed expressed in miles per hour (mph) by 100.
(See figure 1.) The result is the approximate distance the balloon will
travel during its first minute of flight. Next, estimate the height of
the obstacle and add the amount of clearance desired when passing over
the obstacle; e.g., a 100-foot obstacle plus 200 feet of desired clearance
over the obstacle totals 300 feet. Lay the balloon out at least the computed
distance from the obstacle. Upon takeoff, establish an initial rate of
climb of 300 feet per minute (fpm).
The balloon should clear the
obstacle by 200 feet. In another example, the wind speed is 4 mph and there is a
75-foot line of trees downwind at the end of the field. Using the above formula,
multiply the wind speed by 100 (4 x 100 = 400). In order to pass 100 feet over
the trees after takeoff, add 100 feet to the tree height of 75 feet, resulting
in a total of 175 feet. Lay the basket at least 400 feet upwind of the beeline.
Upon takeoff, establish a minimum initial rate of climb of 175 fpm. The balloon
should pass 100 feet over the trees.
2 MPH X 100 200 feet
4 MPH X 100 400 feet
6 MPH X 100 600 feet
8 MPH X 100 800 feet
10 MPH X 100 1000 feet
c. To provide an allowance for errors in distance estimation and changes
in surface wind or other unforeseen occurrences, pick out a significant
landmark halfway to the obstruction. If it should appear that the balloon
will not achieve a minimum of half the clearance altitude by that halfway
point, immediately terminate the flight by activating the deflation port
("rip out") before reaching a critical altitude (usually about 20 feet
above the surface).
d. With a small launch site and close obstacles, it may be appropriate
to issue the "weight off" instruction before launch to accomplish a rapid
initial rate of ascent. Whatever takeoff procedure is used, the ascent
profile should ensure safe and expeditious clearance over and around all
obstacles along the departure path. It is also important to maintain a
positive rate of climb during the departure until the balloon is at or
above the appropriate minimum safe altitude prescribed in § 91.119
in VFR conditions.
CRUISE FLIGHT.
Once established in cruise flight, care must be exercised to maintain
visual flight rules (VFR) visibility and cloud clearance requirements (§
91.155).
a. Class G Airspace - 1,200 feet or less above the surface (regardless
of mean sea level (MSL) altitude).
(1) Day - 1 statute mile visibility and clear of clouds. (See figure
2.)
(2) Night - 3 statute miles visibility and 500 feet below, 1,000 feet
above, and 2,000 feet horizontally from clouds. (See figure 3.) Pilots
should consult § 91.126 for additional requirements when operating
on or in the vicinity of an airport in Class G Airspace.
b. Class G Airspace - more than 1,200 feet above the surface but less
than 10,000 feet MSL.
(1) Day - I statute mile visibility and 500 feet below, 1,000 feet above,
and 2,000 feet horizontally from clouds. (See figure 4.)
(2) Night - 3 statute miles visibility and 500 feet below, 1,000 feet
above, and 2,000 feet horizontally from clouds. (See figure
3.)
c. Class G Airspace at more than 1,200 feet above the surface and at
or above 10,000 feet MSL - 5 statute miles visibility and 1,000 feet below,
1,000 feet above, and 1 statute mile horizontally from clouds. (See figure
5.)
d. Class E Airspace at less than 10,000 feet MSL - 3 statute miles visibility
and 500 feet below, 1,000 feet above, and 2,000 feet horizontally from
clouds. (See figure 6.)
e. Class E Airspace at or above 10,000 feet MSL - 5 statute miles visibility
and 1,000 feet below 1,000 feet above, and 1 statute mile horizontally
from clouds. (See figure 7.) Pilots should consult § 91.127 for additional
requirements when operating on or in the vicinity of an airport in Class
E Airspace.
f. Class D Airspace - 3 statute miles visibility and 500 feet below,
1,000 feet above, and 2,000 feet horizontally from clouds. Pilots should
consult § 91.129 for additional requirements to operate in Class D
Airspace. (See figure 6.)
g. Class C Airspace - 3 statute miles visibility and 500 feet below,
1,000 feet above, and 2,000 feet horizontally from clouds. Pilots should
consult § 91.130 for additional requirements to operate in Class C
Airspace. (See figure 6.)
h. Class B Airspace - 3 statute miles visibility and clear of clouds.
Pilots should consult § 91.131 for additional requirements to operate
in Class B Airspace. (See figure 8.)
i. Class A Airspace - not frequently used by hot air balloons. See §
91.135 for requirements to operate in Class A Airspace.
MINIMUM ALTITUDES.
a. In accordance with § 91.119, balloons must maintain a safe minimum
altitude above the surface and safe minimum distances from obstacles. Section
91.119(b) requires that all aircraft, except when necessary for takeoff
and landing, operate over congested areas of cities, towns, or settlements
or over open air assemblies of persons at an altitude no lower than 1,000
feet above the highest obstacle within a horizontal radius of 2,000 feet
of the aircraft. (See figure 9.)
b. Section 91.119(c) requires that all aircraft, except when necessary
for takeoff and landing, operate over other than congested areas at an
altitude of 500 feet above the surface except over open water or sparsely
populated areas. (See figure 10.)
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.)
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 fields 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 to determine lower
level wind velocities and directions so that options may be considered
until the final descent phase to touchdown. There are other methods to
evaluate lower level wind conditions such as dropping blades of grass,
biodegradable strips of paper, or small balloons. While the descent path
can be varied and 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.
(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.
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
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).
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 left.
(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.
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.
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.
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.
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.
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