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1. Traffic information.
2. Instructions to follow an aircraft; and
3. The acceptance of a visual approach
clearance.
d. For operations conducted behind heavy air-
craft, ATC will specify the word “heavy” when this
information is known. Pilots of heavy aircraft should
always use the word “heavy” in radio communica-
tions.
e. Heavy and large jet aircraft operators should use
the following procedures during an approach to
landing. These procedures establish a dependable
baseline from which pilots of in-trail, lighter aircraft
may reasonably expect to make effective flight path
adjustments to avoid serious wake vortex turbulence.
1. Pilots of aircraft that produce strong wake
vortices should make every attempt to fly on the
established glidepath, not above it; or, if glidepath
guidance is not available, to fly as closely as possible
to a “3-1” glidepath, not above it.
EXAMPLE-
Fly 3,000 feet at 10 miles from touchdown, 1,500 feet at 5
miles, 1,200 feet at 4 miles, and so on to touchdown.
AIM 2/14/08
7-3-7
Wake Turbulence
2. Pilots of aircraft that produce strong wake
vortices should fly as closely as possible to the
approach course centerline or to the extended
centerline of the runway of intended landing as
appropriate to conditions.
f. Pilots operating lighter aircraft on visual
approaches in-trail to aircraft producing strong wake
vortices should use the following procedures to assist
in avoiding wake turbulence. These procedures apply
only to those aircraft that are on visual approaches.
1. Pilots of lighter aircraft should fly on or
above_the glidepath. Glidepath reference may be
furnished by an ILS, by a visual approach slope
system, by other ground-based approach slope
guidance systems, or by other means. In the absence
of visible glidepath guidance, pilots may very nearly
duplicate a 3-degree glideslope by adhering to the
“3_to 1” glidepath principle.
EXAMPLE-
Fly 3,000 feet at 10 miles from touchdown, 1,500 feet at
5_miles, 1,200 feet at 4 miles, and so on to touchdown.
2. If the pilot of the lighter following aircraft has
visual contact with the preceding heavier aircraft and
also with the runway, the pilot may further adjust for
possible wake vortex turbulence by the following
practices:
(a) Pick a point of landing no less than
1,000_feet from the arrival end of the runway.
(b) Establish a line-of-sight to that landing
point that is above and in front of the heavier
preceding aircraft.
(c) When possible, note the point of landing
of the heavier preceding aircraft and adjust point of
intended landing as necessary.
EXAMPLE-
A puff of smoke may appear at the 1,000-foot markings of
the runway, showing that touchdown was that point;
therefore, adjust point of intended landing to the
1,500-foot markings.
(d) Maintain the line-of-sight to the point of
intended landing above and ahead of the heavier
preceding aircraft; maintain it to touchdown.
(e) Land beyond the point of landing of the
preceding heavier aircraft.
3. During visual approaches pilots may ask ATC
for updates on separation and groundspeed with
respect to heavier preceding aircraft, especially when
there is any question of safe separation from wake
turbulence.
7-3-9. Air Traffic Wake Turbulence
Separations
a. Because of the possible effects of wake
turbulence, controllers are required to apply no less
than specified minimum separation for aircraft
operating behind a heavy jet and, in certain instances,
behind large nonheavy aircraft (i.e., B757 aircraft).
1. Separation is applied to aircraft operating
directly behind a heavy/B757 jet at the same altitude
or less than 1,000 feet below:
(a) Heavy jet behind heavy jet-4 miles.
(b) Large/heavy behind B757 - 4 miles.
(c) Small behind B757 - 5 miles.
(d) Small/large aircraft behind heavy jet -
5_miles.
2. Also, separation, measured at the time the
preceding aircraft is over the landing threshold, is
provided to small aircraft:
(a) Small aircraft landing behind heavy jet -
6 miles.
(b) Small aircraft landing behind B757 -
5 miles.
(c) Small aircraft landing behind large
aircraft- 4 miles.
REFERENCE-
Pilot/Controller Glossary Term- Aircraft Classes.
3. Additionally, appropriate time or distance
intervals are provided to departing aircraft:
(a) Two minutes or the appropriate 4 or 5 mile
radar separation when takeoff behind a heavy/B757
jet will be:
(1) From the same threshold.
(2) On a crossing runway and projected
flight paths will cross.
(3) From the threshold of a parallel runway
when staggered ahead of that of the adjacent runway
by less than 500 feet and when the runways are
separated by less than 2,500 feet.
NOTE-
Controllers may not reduce or waive these intervals.
AIM 2/14/08
7-3-8 Wake Turbulence
b. A 3-minute interval will be provided when a
small aircraft will takeoff:
1. From an intersection on the same runway
(same or opposite direction) behind a departing large
aircraft,
2. In the opposite direction on the same runway
behind a large aircraft takeoff or low/missed
approach.
NOTE-
This 3-minute interval may be waived upon specific pilot
request.
c. A 3-minute interval will be provided for all
aircraft taking off when the operations are as
described in subparagraph b1 and 2 above, the
preceding aircraft is a heavy/B757 jet, and the
operations are on either the same runway or parallel
runways separated by less than 2,500 feet.
Controllers may not reduce or waive this interval.
d. Pilots may request additional separation i.e.,
2_minutes instead of 4 or 5 miles for wake turbulence
avoidance. This request should be made as soon as
practical on ground control and at least before taxiing
onto the runway.
NOTE14 CFR Section 91.3(a) states: “The pilot-in-command of
an aircraft is directly responsible for and is the final
authority as to the operation of that aircraft.”
e. Controllers may anticipate separation and need
not withhold a takeoff clearance for an aircraft
departing behind a large/heavy aircraft if there is
reasonable assurance the required separation will
exist when the departing aircraft starts takeoff roll.
AIM 2/14/08
7-4-1
Bird Hazards and Flight Over National Refuges, Parks, and Forests
Section 4. Bird Hazards and Flight Over National
Refuges, Parks, and Forests
7-4-1. Migratory Bird Activity
a. Bird strike risk increases because of bird
migration during the months of March through April,
and August through November.
b. The altitudes of migrating birds vary with winds
aloft, weather fronts, terrain elevations, cloud
conditions, and other environmental variables. While
over 90 percent of the reported bird strikes occur at or
below 3,000 feet AGL, strikes at higher altitudes are
common during migration. Ducks and geese are
frequently observed up to 7,000 feet AGL and pilots
are cautioned to minimize en route flying at lower
altitudes during migration.
c. Considered the greatest potential hazard to
aircraft because of their size, abundance, or habit of
flying in dense flocks are gulls, waterfowl, vultures,
hawks, owls, egrets, blackbirds, and starlings.
Four_major migratory flyways exist in the U.S. The
Atlantic flyway parallels the Atlantic Coast. The
Mississippi Flyway stretches from Canada through
the Great Lakes and follows the Mississippi River.
The Central Flyway represents a broad area east of the
Rockies, stretching from Canada through Central
America. The Pacific Flyway follows the west coast
and overflies major parts of Washington, Oregon, and
California. There are also numerous smaller flyways
which cross these major north-south migratory
routes.
7-4-2. Reducing Bird Strike Risks
a. The most serious strikes are those involving
ingestion into an engine (turboprops and turbine jet
engines) or windshield strikes. These strikes can
result in emergency situations requiring prompt
action by the pilot.
b. Engine ingestions may result in sudden loss of
power or engine failure. Review engine out
procedures, especially when operating from airports
with known bird hazards or when operating near high
bird concentrations.
c. Windshield strikes have resulted in pilots
experiencing confusion, disorientation, loss of
communications, and aircraft control problems.
Pilots are encouraged to review their emergency
procedures before flying in these areas.
d. When encountering birds en route, climb to
avoid collision, because birds in flocks generally
distribute themselves downward, with lead birds
being at the highest altitude.
e. Avoid overflight of known areas of bird
concentration and flying at low altitudes during bird
migration. Charted wildlife refuges and other natural
areas contain unusually high local concentration of
birds which may create a hazard to aircraft.
7-4-3. Reporting Bird Strikes
Pilots are urged to report any bird or other wildlife
strike using FAA Form 5200-7, Bird/Other Wildlife
Strike Report (Appendix 1). Additional forms are
available at any FSS; at any FAA Regional Office or
at http://wildlife-mitigation.tc.faa.gov. The data
derived from these reports are used to develop
standards to cope with this potential hazard to aircraft
and for documentation of necessary habitat control on
airports.
7-4-4. Reporting Bird and Other Wildlife
Activities
If you observe birds or other animals on or near the
runway, request airport management to disperse the
wildlife before taking off. Also contact the nearest
FAA ARTCC, FSS, or tower (including non-Federal
towers) regarding large flocks of birds and report the:
a. Geographic location.
b. Bird type (geese, ducks, gulls, etc.).
c. Approximate numbers.
d. Altitude.
e. Direction of bird flight path.
AIM 2/14/08
7-4-2 Bird Hazards and Flight Over National Refuges, Parks, and Forests
7-4-5. Pilot Advisories on Bird and Other
Wildlife Hazards
Many airports advise pilots of other wildlife hazards
caused by large animals on the runway through the
A/FD and the NOTAM system. Collisions of landing
and departing aircraft and animals on the runway are
increasing and are not limited to rural airports. These
accidents have also occurred at several major
airports. Pilots should exercise extreme caution when
warned of the presence of wildlife on and in the
vicinity of airports. If you observe deer or other large
animals in close proximity to movement areas, advise
the FSS, tower, or airport management.
7-4-6. Flights Over Charted U.S. Wildlife
Refuges, Parks, and Forest Service Areas
a. The landing of aircraft is prohibited on lands or
waters administered by the National Park Service,
U.S. Fish and Wildlife Service, or U.S. Forest Service
without authorization from the respective agency.
Exceptions include:
1. When forced to land due to an emergency
beyond the control of the operator;
2. At officially designated landing sites; or
3. An approved official business of the Federal
Government.
b. Pilots are requested to maintain a minimum
altitude of 2,000 feet above the surface of the
following: National Parks, Monuments, Seashores,
Lakeshores, Recreation Areas and Scenic Riverways
administered by the National Park Service, National
Wildlife Refuges, Big Game Refuges, Game Ranges
and Wildlife Ranges administered by the U.S. Fish
and Wildlife Service, and Wilderness and Primitive
areas administered by the U.S. Forest Service.
NOTE-
FAA Advisory Circular AC 91-36, Visual Flight
Rules_(VFR) Flight Near Noise-Sensitive Areas, defines
the surface of a national park area (including parks,
forests, primitive areas, wilderness areas, recreational
areas, national seashores, national monuments, national
lakeshores, and national wildlife refuge and range areas)
as: the highest terrain within 2,000 feet laterally of the
route of flight, or the upper-most rim of a canyon or valley.
c. Federal statutes prohibit certain types of flight
activity and/or provide altitude restrictions over
designated U.S. Wildlife Refuges, Parks, and Forest
Service Areas. These designated areas, for example:
Boundary Waters Canoe Wilderness Areas,
Minnesota; Haleakala National Park, Hawaii;
Yosemite National Park, California; and Grand
Canyon National Park, Arizona, are charted on
Sectional Charts.
d. Federal regulations also prohibit airdrops by
parachute or other means of persons, cargo, or objects
from aircraft on lands administered by the three
agencies without authorization from the respective
agency. Exceptions include:
1. Emergencies involving the safety of human
life; or
2. Threat of serious property loss.
AIM 2/14/08
7-5-1
Potential Flight Hazards
Section 5. Potential Flight Hazards
7-5-1. Accident Cause Factors
a. The 10 most frequent cause factors for general
aviation accidents that involve the pilot-in-command
are:
1. Inadequate preflight preparation and/or
planning.
2. Failure to obtain and/or maintain flying
speed.
3. Failure to maintain direction control.
4. Improper level off.
5. Failure to see and avoid objects or
obstructions.
6. Mismanagement of fuel.
7. Improper inflight decisions or planning.
8. Misjudgment of distance and speed.
9. Selection of unsuitable terrain.
10. Improper operation of flight controls.
b. This list remains relatively stable and points out
the need for continued refresher training to establish
a higher level of flight proficiency for all pilots. A
part of the FAA's continuing effort to promote
increased aviation safety is the Aviation Safety
Program. For information on Aviation Safety
Program activities contact your nearest Flight
Standards District Office.
c. Alertness. Be alert at all times, especially
when the weather is good. Most pilots pay attention
to business when they are operating in full IFR
weather conditions, but strangely, air collisions
almost invariably have occurred under ideal weather
conditions. Unlimited visibility appears to encourage
a sense of security which is not at all justified.
Considerable information of value may be obtained
by listening to advisories being issued in the terminal
area, even though controller workload may prevent a
pilot from obtaining individual service.
d. Giving Way. If you think another aircraft is too
close to you, give way instead of waiting for the other
pilot to respect the right-of-way to which you may be
entitled. It is a lot safer to pursue the right-of-way
angle after you have completed your flight.
7-5-2. VFR in Congested Areas
A high percentage of near midair collisions occur
below 8,000 feet AGL and within 30 miles of an
airport. When operating VFR in these highly
congested areas, whether you intend to land at an
airport within the area or are just flying through, it is
recommended that extra vigilance be maintained and
that you monitor an appropriate control frequency.
Normally the appropriate frequency is an approach
control frequency. By such monitoring action you can
“get the picture” of the traffic in your area. When the
approach controller has radar, radar traffic advisories
may be given to VFR pilots upon request.
REFERENCE-
AIM, Paragraph 4-1-14, Radar Traffic Information Service.
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 (NOTAMs) are issued on those lighted
structures experiencing temporary light outages.
However, some time may pass before the FAA is
notified of these outages, and the 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
AIM 2/14/7-5-2 Potential Flight Hazards
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.
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.
7-5-5. Unmanned Aircraft Systems
a. Unmanned Aircraft Systems (UAS), formerly
referred to as “Unmanned Aerial Vehicles” (UAVs)
or “drones,” are having an increasing operational
presence in the NAS. Once the exclusive domain of
the military, UAS are now being operated by various
entities. Although these aircraft are “unmanned,”
UAS are flown by a remotely located pilot and crew.
Physical and performance characteristics of unmanned aircraft (UA) vary greatly and unlike model
aircraft that typically operate lower than 400 feet
AGL, UA may be found operating at virtually any
altitude and any speed. Sizes of UA can be as small
as several pounds to as large as a commercial
transport aircraft. UAS come in various categories
including airplane, rotorcraft, powered-lift (tilt-
rotor), and lighter-than-air. Propulsion systems of
UAS include a broad range of alternatives from
piston powered and turbojet engines to battery and
solar-powered electric motors.
b. To ensure segregation of UAS operations from
other aircraft, the military typically conducts UAS
operations within restricted or other special use
airspace. However, UAS operations are now being
approved in the NAS outside of special use airspace
through the use of FAA-issued Certificates of Waiver
or Authorization (COA) or through the issuance of a
special airworthiness certificate. COA and special
airworthiness approvals authorize UAS flight
operations to be contained within specific geographic
boundaries and altitudes, usually require coordination with an ATC facility, and typically require the
issuance of a NOTAM describing the operation to be
conducted. UAS approvals also require observers to
provide “see-and-avoid” capability to the UAS crew
and to provide the necessary compliance with 14 CFR
Section 91.113. For UAS operations approved at or
above FL180, UAS operate under the same
requirements as that of manned aircraft (i.e., flights
3/15/07 7110.65R CHG 2 AIM 7/31/08
AIM 2/14/08
7-5-3
Potential Flight Hazards
are operated under instrument flight rules, are in
communication with ATC, and are appropriately
equipped).
c. UAS operations may be approved at either
controlled or uncontrolled airports and are typically
disseminated by NOTAM. In all cases, approved
UAS operations shall comply with all applicable
regulations and/or special provisions specified in the
COA or in the operating limitations of the special
airworthiness certificate. At uncontrolled airports,
UAS operations are advised to operate well clear of
all known manned aircraft operations. Pilots of
manned aircraft are advised to follow normal
operating procedures and are urged to monitor the
CTAF for any potential UAS activity. At controlled
airports, local ATC procedures may be in place to
handle UAS operations and should not require any
special procedures from manned aircraft entering or
departing the traffic pattern or operating in the
vicinity of the airport.
d. In addition to approved UAS operations
described above, a recently approved agreement
between the FAA and the Department of Defense
authorizes small UAS operations wholly contained
within Class G airspace, and in no instance, greater
than 1200 feet AGL over military owned or leased
property. These operations do not require any special
authorization as long as the UA remains within the
lateral boundaries of the military installation as well
as other provisions including the issuance of a
NOTAM. Unlike special use airspace, these areas
may not be depicted on an aeronautical chart.
e. There are several factors a pilot should consider
regarding UAS activity in an effort to reduce
potential flight hazards. Pilots are urged to exercise
increased vigilance when operating in the vicinity of
restricted or other special use airspace, military
operations areas, and any military installation. Areas
with a preponderance of UAS activity are typically
noted on sectional charts advising pilots of this
activity. Since the size of a UA can be very small, they
may be difficult to see and track. If a UA is
encountered during flight, as with manned aircraft,
never assume that the pilot or crew of the UAS can see
you, maintain increased vigilance with the UA and
always be prepared for evasive action if necessary.
Always check NOTAMs for potential UAS activity
along the intended route of flight and exercise
increased vigilance in areas specified in the NOTAM.
7-5-6. 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.
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. Understand Mountain Obscuration. The
term Mountain Obscuration (MTOS) is used to
describe a visibility condition that is distinguished
from IFR because ceilings, by definition, are
described as “above ground level” (AGL). In
mountainous terrain clouds can form at altitudes
significantly higher than the weather reporting
station and at the same time nearby mountaintops
may be obscured by low visibility. In these areas the
ground level can also vary greatly over a small area.
Beware if operating VFR-on-top. You could be
operating closer to the terrain than you think because
the tops of mountains are hidden in a cloud deck
below. MTOS areas are identified daily on The
Aviation Weather Center located at:
http://www.aviationweather.gov.
7/31/08 AIM
AIM 2/14/7-5-4 Potential Flight Hazards
f. 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!
g. 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.
h. 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.
i. 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.
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.
j. Mountain Wave. Many pilots go all their lives
without understanding what a mountain wave is.
Quite a few have lost their lives because of this lack
of understanding. One need not be a licensed
meteorologist to understand the mountain wave
phenomenon.
3/15/07 7110.65R CHG 2 AIM 7/31/08
AIM 2/14/08
7-5-5
Potential Flight Hazards
1. Mountain waves occur when air is being
blown over a mountain range or even the ridge of a
sharp bluff area. As the air hits the upwind side of the
range, it starts to climb, thus creating what is
generally a smooth updraft which turns into a
turbulent downdraft as the air passes the crest of the
ridge. From this point, for many miles downwind,
there will be a series of downdrafts and updrafts.
Satellite photos of the Rockies have shown mountain
waves extending as far as 700 miles downwind of the
range. Along the east coast area, such photos of the
Appalachian chain have picked up the mountain
wave phenomenon over a hundred miles eastward.
All it takes to form a mountain wave is wind blowing
across the range at 15 knots or better at an intersection
angle of not less than 30 degrees.
2. Pilots from flatland areas should understand
a few things about mountain waves in order to stay
out of trouble. When approaching a mountain range
from the upwind side (generally the west), there will
usually be a smooth updraft; therefore, it is not quite
as dangerous an area as the lee of the range. From the
leeward side, it is always a good idea to add an extra
thousand feet or so of altitude because downdrafts
can exceed the climb capability of the aircraft. Never
expect an updraft when approaching a mountain
chain from the leeward. Always be prepared to cope
with a downdraft and turbulence.
3. When approaching a mountain ridge from the
downwind side, it is recommended that the ridge be
approached at approximately a 45 degree angle to the
horizontal direction of the ridge. This permits a safer
retreat from the ridge with less stress on the aircraft
should severe turbulence and downdraft be experienced. If severe turbulence is encountered,
simultaneously reduce power and adjust pitch until
aircraft approaches maneuvering speed, then adjust
power and trim to maintain maneuvering speed and
fly away from the turbulent area.
7-5-7. Use of Runway Half-way Signs at
Unimproved Airports
When installed, runway half-way signs provide the
pilot with a reference point to judge takeoff
acceleration trends. Assuming that the runway length
is appropriate for takeoff (considering runway
condition and slope, elevation, aircraft weight, wind,
and temperature), typical takeoff acceleration should
allow the airplane to reach 70 percent of lift-off
airspeed by the midpoint of the runway. The “rule of
thumb” is that should airplane acceleration not allow
the airspeed to reach this value by the midpoint, the
takeoff should be aborted, as it may not be possible to
liftoff in the remaining runway.
Several points are important when considering using
this “rule of thumb”:
a. Airspeed indicators in small airplanes are not
required to be evaluated at speeds below stalling, and
may not be usable at 70 percent of liftoff airspeed. |
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