|
Excerpts from the Aeronautical Information Manual are reprinted below. They
contain information that GA pilots should be aware of when operating at low altitude.
( Some additional editorial comments have been added to a few paragraphs to
highlight certain CFIT risks or possible operating methods to reduce such risks.
Aviation will always have an element of risk. A knowledgeable pilot will try to
reduce these risks to an acceptable level. These additional comments are in
italic and identified as AC Comments.)
7-5-3, Obstructions to Flight.
a. General. Many structures exist that could significantly affect the safety of
your flight when operating below 500 feet AGL, and particularly below 200 feet AGL.
While 14 CFR Part 91.119 allows flight below 500 AGL when over sparsely populated
areas or open water, such operations are very dangerous. At and below 200 feet
AGL there are numerous power lines, antenna towers, etc., that are not marked and
lighted as obstructions and therefore may not be seen in time to avoid a collision.
Notices to Airmen (NOTAM) are issued on those lighted structures experiencing
temporary light outages. However, some time may pass before the FAA is notified
of these outages, and a NOTAM issued, thus pilot vigilance is imperative.
b. Antenna Towers. Extreme caution should be exercised when flying less than
2,000 feet AGL because of numerous skeletal structures, such as radio and television
antenna towers, that exceed 1,000 feet AGL with some extending higher than 2,000 feet
AGL. Most skeletal structures are supported by guy wires which are very difficult
to see in good weather and can be invisible at dusk or during periods of reduced
visibility. These wires can extend about 1,500 feet horizontally from a structure;
therefore, all skeletal structures should be avoided horizontally by at least
2,000 feet. Additionally, new towers may not be on your current chart because the
information was not received prior to the printing of the chart.
Every pilot must remember that not every tower has to be published on
aeronautical charts. Chart clutter may limit the printing of some towers.
Other towers are not required to be listed because they are not tall enough.
A builder may simply not report a new tower. Equally dangerous is a new tower's
position may be wrong. Because of these factors, pilots are cautioned to be
particularly careful when operating at low altitude. The "see and avoid"
rule becomes critical close to the ground. A lesson taken from the helicopter
community is to fly overhead at a safe altitude and check the area for towers
and hazards before descending to a lower altitude where a CFIT accident is likely
to occur.
AC Comment: In some cases, the information is published in the next
Airport/Facility Directory's Aeronautical Chart Bulletin section, but the pilot
fails to make the necessary corrections to the chart.
c. Overhead Wires. Overhead transmission and utility lines often span approaches
to runways, natural flyways such as lakes, rivers, gorges, and canyons, and cross
other landmarks pilots frequently follow such as highways, railroad tracks, etc. As
with antenna towers, these high voltage/power lines or the supporting structures of
these lines may not always be readily visible and the wires may be virtually impossible
to see under certain conditions. In some locations, the supporting structures of
overhead transmission lines are equipped with unique sequence flashing white strobe
light systems to indicate that there are wires between the structures. However,
many power lines do not require notice to the FAA and, therefore, are not marked
and/or lighted. Many of those that do require notice do not exceed 200 feet AGL
or meet the Obstruction Standard of 14 CFR Part 77 and, therefore, are not marked
and/or lighted. All pilots are cautioned to remain extremely vigilant for these
power lines or their supporting structures when following natural flyways or
during the approach and landing phase. This is particularly important for
seaplane and/or float equipped aircraft when landing on, or departing from,
unfamiliar lakes or rivers.
d. Other Objects/Structures. There are other objects or structures that could
adversely affect your flight such as construction cranes near an airport, newly
constructed buildings, new towers, etc. Many of these structures do not meet
charting requirements or may not yet be charted because of the charting cycle.
Some structures do not require obstruction marking and/or lighting and some may
not be marked and lighted even though the FAA recommended it.
7-5-4. Avoid Flight Beneath Unmanned Balloons.
a. The majority of unmanned free balloons currently being operated have,
extending below them, either a suspension device to which the payload or instrument
package is attached, or a trailing wire antenna, or both. In many instances, these
balloon subsystems may be invisible to the pilot until the aircraft is close to the
balloon, thereby creating a potentially dangerous situation. Therefore, good judgment
on the part of the pilot dictates that aircraft should remain well clear of all
unmanned free balloons and flight below them should be avoided at all times.
b. Pilots are urged to report any unmanned free balloons sighted to the nearest
FAA ground facility with which communication is established. Such information will
assist FAA ATC facilities to identify and flight follow unmanned free balloons operating
in the airspace.
AC Comment: In addition to unmanned free balloons, the U.S. Government operates
unmarked balloons thousands of feet into the sky tethered to cables. These balloons
are contained in published restricted areas. Located primarily along the southern U.S.
border, pilots are advised to check their charts for the location of these unmarked
tethered balloons when flying through areas they are not familiar with. These
balloons may be at an altitude of more than 10,000 feet AGL.
7-5-5. Mountain Flying.
a. Your first experience of flying over mountainous terrain (particularly if most of
your flight time has been over the flatlands of the Midwest) could be a
never-to-be-forgotten nightmare if proper planning is not done and if you are not
aware of the potential hazards awaiting. Those familiar section lines are not present
in the mountains; those flat, level fields for forced landings are practically
nonexistent; abrupt changes in wind direction and velocity occur; severe updrafts
and downdrafts are common, particularly near or above abrupt changes of terrain such
as cliffs or rugged areas; even the clouds look different and can build up with
startling rapidity. Mountain flying need not be hazardous if you follow the
recommendations below.
AC Comment: As in all types of new flying, you should find a qualified
and currently certificated flight instructor for a local area checkout.
b. File a flight plan. Plan your route to avoid topography which would prevent
a safe forced landing. The route should be over populated areas and well-known
mountain passes. Sufficient altitude should be maintained to permit gliding to a
safe landing in the event of engine failure.
c. Don't fly a light aircraft when the winds aloft, at your proposed altitude,
exceed 35 miles per hour. Expect the winds to be of much greater velocity over
mountain passes than reported a few miles from them. Approach mountain passes with
as much altitude as possible. Downdrafts of from 1,500 to 2,000 feet per minute
are not uncommon on the leeward side.
d. Don't fly near or above abrupt changes in terrain. Severe turbulence can be
expected, especially in high wind conditions.
e. Some canyons run into a dead end. Don't fly so far up a canyon that you get
trapped. Always be able to make a 180 degree turn!
f. VFR flight operations may be conducted at night in mountainous terrain with
the application of sound judgment and common sense. Proper pre-flight planning,
giving ample consideration to winds and weather, knowledge of the terrain and pilot
experience in mountain flying are prerequisites for safety of flight. Continuous
visual contact with the surface and obstructions is a major concern and flight
operations under an overcast or in the vicinity of clouds should be approached
with extreme caution.
g. When landing at a high altitude field, the same indicated airspeed should
be used as at low elevation fields. Remember: that due to the less dense air at
altitude, this same indicated airspeed actually results in higher true airspeed,
a faster landing speed, and more important, a longer landing distance. During
gusty wind conditions which often prevail at high altitude fields, a power
approach and power landing is recommended. Additionally, due to the faster
groundspeed, your takeoff distance will increase considerably over that required
at low altitudes.
h. Effects of Density Altitude. Performance figures in the aircraft owner's
handbook for length of takeoff run, horsepower, rate of climb, etc., are generally
based on standard atmosphere conditions (59 degrees Fahrenheit (15 degrees Celsius),
pressure 29.92 inches of mercury) at sea level. However, inexperienced pilots, as
well as experienced pilots, may run into trouble when they encounter an altogether
different set of conditions. This is particularly true in hot weather and at higher
elevations. Aircraft operations at altitudes above sea level and at higher than
standard temperatures are commonplace in mountainous areas. Such operations quite
often result in a drastic reduction of aircraft performance capabilities because of
the changing air density. Density altitude is a measure of air density. It is not
to be confused with pressure altitude, true altitude, or absolute altitude. It is
not to be used as a height reference, but as a determining criteria in the performance
capability of an aircraft. Air density decreases with altitude. As air density
decreases, density altitude increases. The further effects of high temperature
and high humidity are cumulative, resulting in an increasing high-density altitude
condition. High-density altitude reduces all aircraft performance parameters. To
the pilot, this means that the normal horsepower output is reduced, propeller
efficiency is reduced and a higher true airspeed is required to sustain the aircraft
throughout its operating parameters. It means an increase in runway length requirements
for takeoff and landings, and decreased rate of climb. An average small airplane,
for example, requiring 1,000 feet for takeoff at sea level under standard atmospheric
conditions will require a takeoff run of approximately 2,000 feet at an operational
altitude of 5,000 feet.
NOTE: A turbo-charged aircraft engine provides some slight advantage in that it
provides sea level horsepower up to a specified altitude above sea level.
AC Comment: A turbo-charged aircraft can provide a significant operating
advantage if operated within its approved limitations. In some cases, a turbo-charged,
high performance aircraft may be the only safe way to fly into and out of some
mountain landing areas.
(1) Density Altitude Advisories. At airports with elevations of 2,000 feet and
higher, control towers and FSSs will broadcast the advisory "Check Density
Altitude" when the temperature reaches a predetermined level. These
advisories will be broadcast on appropriate tower frequencies or, where available,
ATIS. FSSs will broadcast these advisories as a part of Local Airport Advisory,
and on TWEB.
(2) These advisories are provided by air traffic facilities, as a reminder to
pilots that high temperatures and high field elevations will cause significant
changes in aircraft characteristics. The pilot retains the responsibility to
compute density altitude, when appropriate, as a part of preflight duties.
NOTE: All FSSs will compute the current density altitude upon request.
|
