Color and Type of Signal Aircraft on the GroundMovement of Vehicles,
Equipment and Personnel Aircraft in Flight
Steady green
Flashing green
Steady red
Flashing red
Flashing white
Alternating red and green
Cleared to cross,
proceed or go
Not applicable
Stop
Clear the taxiway/runway
Return to starting point
on airport
Exercise extreme caution!!!!
Cleared for takeoff
Cleared for taxi
Stop
Taxi clear of the runway
in use
Return to starting point
on airport
Exercise extreme caution!!!!
Cleared to land
Return for landing (to be followed
by steady green at the proper time)
Give way to other aircraft and
continue circling
Airport unsafe, do not land
Not applicable
Exercise extreme caution!!!!
Figure 14-42. Light gun signals.
Radar Beacon Phraseology
SQUAWK (number)
IDENT
SQUAWK (number) and IDENT
SQUAWK Standby
SQUAWK Low/Normal
SQUAWK Altitude
STOP Altitude SQUAWK
STOP SQUAWK (mode in use)
STOP SQUAWK
SQUAWK Mayday
SQUAWK VFR
Operate radar beacon transponder on designated code in MODE A/3.
Engage the “IDENT” feature (military I/P) of the transponder.
Operate transponder on specified code in MODE A/3 and engage the “IDENT”
(military I/P) feature.
Switch transponder to standby position.
Operate transponder on low or normal sensitivity as specified. Transponder is
operated in “NORMAL” position unless ATC specifies “LOW” (“ON” is used instead of
“NORMAL” as a master control label on some types of transponders).
Activate MODE C with automatic altitude reporting.
Turn off altitude reporting switch and continue transmitting MODE C framing pulses.
If your equipment does not have this capability, turn off MODE C.
Switch off specified mode. (Used for military aircraft when the controller is unaware of
military service requirements for the aircraft to continue operation on another MODE.)
Switch off transponder.
Operate transponder in the emergency position (MODE A Code 7700 for civil
transponder, MODE 3 Code 7700 and emergency feature for military transponder).
Operate radar beacon transponder on Code 1200 in MODE A/3, or other
appropriate VFR code.
Figure 14-43. Transponder phraseology.
provides all the same information the ATCRBS, but will do
so more rapidly and with significantly more accuracy. By
broadcasting aircraft position information to a ground station,
ADS–B can also provide coverage in areas that do not have
radar coverage. In addition, ADS–B provides trajectory
information that includes speed and direction of motion.
Transponder
The transponder is the airborne portion of the secondary
surveillance radar system and a system with which a pilot
should be familiar. The ATCRBS cannot display the secondary
information unless an aircraft is equipped with a transponder.
A transponder is also required to operate in certain controlled
airspace as discussed in Chapter 15, “Airspace.”
A transponder code consists of four numbers from 0 to 7
(4,096 possible codes). There are some standard codes or ATC
may issue a four-digit code to an aircraft. When a controller
requests a code or function on the transponder, the word
“squawk” may be used. Figure 14-43 lists some standard
transponder phraseology. Additional information concerning
transponder operation can be found in the AIM, Chapter 4.
TRACK TRACK
Traffic information would be issued to the pilot of aircraft “A”
as 12 o’clock. The actual position of the traffic as seen by
the pilot of aircraft “A” would be 1 o’clock. Traffic information
issued to aircraft “B” would also be given as 12 o’clock, but
in this case, the pilot of “B” would see traffic at 10 o’clock.
Wind
A B
Figure 14-44. Traffic advisories.
Automatic Dependent Surveillance–Broadcast
(ADS-B)
Automatic Dependent Surveillance−Broadcast (ADS−B) is a
surveillance technology being deployed throughout the NAS
to facilitate improvements needed to increase the capacity
and efficiency of the NAS, while maintaining safety. ADS-B
supports these improvements by providing a higher update rate
and enhanced accuracy of surveillance information over the
current radar-based surveillance system. In addition, ADS-B
enables the expansion of air traffic control (ATC) surveillance
services into areas where none existed previously. The ADS-B
ground system also provides Traffic Information Services-
Broadcast (TIS-B) and Flight Information Services-Broadcast
(FIS-B) for use on appropriately equipped aircraft, enhancing
the user’s situational awareness (SA) and improving the
overall safety of the NAS.
The ADS−B system is composed of aircraft avionics and a
ground infrastructure. Onboard avionics determine the position
of the aircraft by using the GPS and transmit its position,
along with additional information about the aircraft, to ground
stations for use by ATC and nearby ADS-B equipped aircraft.
In the United States, ADS−B equipped aircraft exchange
information on one of two frequencies: 978 or 1090 MHz.
The 1090 MHz frequency is associated with Mode A, C, and S
transponder operations. 1090 MHz transponders with integrated
ADS−B functionality extend the transponder message sets with
additional ADS−B information. This additional information
is known as an “extended squitter” message and referred to as
1090ES. ADS−B equipment operating on 978 MHz is known
as the Universal Access Transceiver (UAT).
Radar Traffic Advisories
Radar equipped ATC facilities provide radar assistance
to aircraft on instrument flight plans and VFR aircraft
provided the aircraft can communicate with the facility and
are within radar coverage. This basic service includes safety
alerts, traffic advisories, limited vectoring when requested,
and sequencing at locations where this procedure has been
established. ATC issues traffic advisories based on observed
radar targets. The traffic is referenced by azimuth from the
aircraft in terms of the 12-hour clock. Also, distance in
nautical miles, direction in which the target is moving, and
type and altitude of the aircraft, if known, are given.
An example would be: “Traffic 10 o’clock 5 miles east
bound, Cessna 152, 3,000 feet.” The pilot should note that
traffic position is based on the aircraft track and that wind
correction can affect the clock position at which a pilot locates
traffic. This service is not intended to relieve the pilot of the
responsibility to see and avoid other aircraft. [Figure 14-44]
In addition to basic radar service, terminal radar service
area (TRSA) has been implemented at certain terminal
locations. TRSAs are depicted on sectional aeronautical
charts and listed in the Chart Supplement U.S. (formerly
Airport/Facility Directory). The purpose of this service is to
provide separation between all participating VFR aircraft and
all IFR aircraft operating within the TRSA. Class C service
provides approved separation between IFR and VFR aircraft
and sequencing of VFR aircraft to the primary airport. Class
B service provides approved separation of aircraft based on
IFR, VFR, and/or weight and sequencing of VFR arrivals to
the primary airport(s).
Wake Turbulence
All aircraft generate wake turbulence during flight. This
disturbance is caused by a pair of counter-rotating vortices
trailing from the wingtips. The vortices from larger aircraft
pose problems to encountering aircraft. The wake of these
aircraft can impose rolling moments exceeding the roll-
control authority of the encountering aircraft. Also, the
turbulence generated within the vortices can damage aircraft
components and equipment if encountered at close range. For
this reason, a pilot must envision the location of the vortex
wake and adjust the flight path accordingly.
Vortex Generation
Lift is generated by the creation of a pressure differential over
the wing surface. The lowest pressure occurs over the upper
wing surface and the highest pressure under the wing. This
pressure differential triggers the rollup of the airflow aft of
the wing resulting in swirling air masses trailing downstream
of the wingtips. After the rollup is completed, the wake
consists of two counter rotating cylindrical vortices. Most of
the energy lies within a few feet of the center of each vortex.
[Figure 14-45]
25
Wake begins
Touchdown
Rotation
Wake ends
Figure 14-46. Vortex behavior.
Figure 14-45. Vortex generation.
Vortex Strength
Terminal Area
Wake turbulence has historically been thought of as only
a function of aircraft weight, but recent research considers
additional parameters, such as speed, aspects of the wing, wake
decay rates, and aircraft resistance to wake, just to name a few.
The vortex characteristics of any aircraft will be changed with
the extension of flaps or other wing configuration devices, as
well as changing speed. However, as the basic factors are weight
and speed, the vortex strength increases proportionately with
an increase in aircraft operating weight or decrease in aircraft
speed. The greatest vortex strength occurs when the generating
aircraft is heavy, slow, and clean, since the turbulence from a
“dirty” aircraft configuration hastens wake decay.
En Route
En route wake turbulence events have been influenced by
changes to the aircraft fleet mix that have more “Super”
(A380) and “Heavy” (B-747, B-777, A340, etc.) aircraft
operating in the NAS. There have been wake turbulence
events in excess of 30NM and 2000 feet lower than the wake
generating aircraft. Air density is also a factor in wake strength.
Even though the speeds are higher in cruise at high altitude,
the reduced air density may result in wake strength comparable
to that in the terminal area. In addition, for a given separation
distance, the higher speeds in cruise result in less time for the
wake to decay before being encountered by a trailing aircraft.
Vortex Behavior
Trailing vortices have certain behavioral characteristics
that can help a pilot visualize the wake location and take
avoidance precautions.
Vortices are generated from the moment an aircraft leaves the
ground (until it touches down), since trailing vortices are the
byproduct of wing lift. [Figure 14-46] The vortex circulation
is outward, upward, and around the wingtips when viewed
from either ahead or behind the aircraft. Tests with large
aircraft have shown that vortices remain spaced a bit less than
a wingspan apart, drifting with the wind, at altitudes greater
than a wingspan from the ground. Tests have also shown that
the vortices sink at a rate of several hundred feet per minute,
slowing their descent and diminishing in strength with time
and distance behind the generating aircraft.
When the vortices of larger aircraft sink close to the ground
(within 100 to 200 feet), they tend to move laterally over
the ground at a speed of 2–3 knots. A crosswind decreases
the lateral movement of the upwind vortex and increases
the movement of the downwind vortex. A light quartering
tailwind presents the worst case scenario as the wake
vortices could be all present along a significant portion of
the final approach and extended centerline and not just in the
touchdown zone as typically expected.
Vortex Avoidance Procedures
The following procedures are in place to assist pilots in vortex
avoidance in the given scenario.
• Landing behind a larger aircraft on the same runway—
stay at or above the larger aircraft’s approach
flight path and land beyond its touchdown point.
[Figure 14-47A]
• Landing behind a larger aircraft on a parallel runway
closer than 2,500 feet—consider the possibility of drift
and stay at or above the larger aircraft’s final approach
flight path and note its touchdown point. [Figure 14-47B]
• Landing behind a larger aircraft on crossing runway—
cross above the larger aircraft’s flight path.
• Landing behind a departing aircraft on the same
runway—land prior to the departing aircraft’s
rotating point.
• Landing behind a larger aircraft on a crossing
runway—note the aircraft’s rotation point and, if that
point is past the intersection, continue and land prior
to the intersection. If the larger aircraft rotates prior
to the intersection, avoid flight below its flight path.
Abandon the approach unless a landing is ensured well
before reaching the intersection. [Figure 14-47C]
• Departing behind a large aircraft—rotate prior to the
large aircraft’s rotation point and climb above its climb
path until turning clear of the wake.
• For intersection takeoffs on the same runway—
be alert to adjacent larger aircraft operations,
particularly upwind of the runway of intended use.
If an intersection takeoff clearance is received, avoid
headings that cross below the larger aircraft’s path.
• If departing or landing after a large aircraft executing
a low approach, missed approach, or touch-and-go
landing (since vortices settle and move laterally
near the ground, the vortex hazard may exist along
the runway and in the flight path, particularly in a
quartering tailwind), it is prudent to wait at least 2
minutes prior to a takeoff or landing.
• En route, it is advisable to avoid a path below and
behind a large aircraft, and if a large aircraft is
observed above on the same track, change the aircraft
position laterally and preferably upwind.
Collision Avoidance
Title 14 of the CFR part 91 has established right-of-way
rules, minimum safe altitudes, and VFR cruising altitudes
to enhance flight safety. The pilot can contribute to collision
avoidance by being alert and scanning for other aircraft. This
is particularly important in the vicinity of an airport.
Effective scanning is accomplished with a series of short,
regularly spaced eye movements that bring successive areas of
the sky into the central visual field. Each movement should not
exceed 10°, and each should be observed for at least 1 second
to enable detection. Although back and forth eye movements
seem preferred by most pilots, each pilot should develop a
scanning pattern that is most comfortable and then adhere to
it to assure optimum scanning. Even if entitled to the right-of-
way, a pilot should yield if another aircraft seems too close.
Clearing Procedures
The following procedures and considerations are in place to
assist pilots in collision avoidance under various situations:
• Before takeoff—prior to taxiing onto a runway or
landing area in preparation for takeoff, pilots should
scan the approach area for possible landing traffic,
executing appropriate maneuvers to provide a clear
view of the approach areas.
• Climbs and descents—during climbs and descents in
flight conditions that permit visual detection of other
traffic, pilots should execute gentle banks left and right
at a frequency that permits continuous visual scanning
of the airspace.
• Straight and level—during sustained periods of
straight-and-level flight, a pilot should execute
appropriate clearing procedures at periodic intervals.
• Traffic patterns—entries into traffic patterns while
descending should be avoided.
• Traffic at VOR sites—due to converging traffic,
sustained vigilance should be maintained in the
vicinity of VORs and intersections.
• Training operations—vigilance should be maintained
and clearing turns should be made prior to a practice
Aircraft crossing over
wake turbulence
Aircraft altitude is above wake
C
Touchdown point
Aircraft altitude is above wake
Less than 2500 feet
WIND
Parallel Runway Situation
B
Touchdown point of larger aircraft
WIND
A
Side view
Figure 14-47. Vortex avoidance procedures.
maneuver. During instruction, the pilot should be
asked to verbalize the clearing procedures (call out
“clear left, right, above, and below”).
High-wing and low-wing aircraft have their respective blind
spots. The pilot of a high-wing aircraft should momentarily
raise the wing in the direction of the intended turn and look
for traffic prior to commencing the turn. The pilot of a low-
wing aircraft should momentarily lower the wing and look
for traffic prior to commencing the turn.
Pilot Deviations (PDs)
A pilot deviation (PD) is an action of a pilot that violates any
Federal Aviation Regulation. While PDs should be avoided,
the regulations do authorize deviations from a clearance in
response to a traffic alert and collision avoidance system
resolution advisory. You must notify ATC as soon as possible
following a deviation.
Pilot deviations can occur in several different ways.
Airborne deviations result when a pilot strays from
an assigned heading or altitude or from an instrument
procedure, or if the pilot penetrates controlled or restricted
airspace without ATC clearance.
To prevent airborne deviations, follow these steps:
• Plan each flight—you may have flown the flight many
times before but conditions and situations can change
rapidly, such as in the case of a pop-up temporary
flight restriction (TFR). Take a few minutes prior to
each flight to plan accordingly.
• Talk and squawk—Proper communication with ATC
has its benefits. Flight following often makes the
controller’s job easier because they can better integrate
VFR and IFR traffic.
• Give yourself some room—GPS is usually more
precise than ATC radar. Using your GPS to fly up
to and along the line of the airspace you are trying to
avoid could result in a pilot deviation because ATC
radar may show you within the restricted airspace.
Ground deviations (also called surface deviations) include
taxiing, taking off, or landing without clearance, deviating
from an assigned taxi route, or failing to hold short of an
assigned clearance limit. To prevent ground deviations, stay
alert during ground operations. Pilot deviations can and
frequently do occur on the ground. Many strategies and tactics
pilots use to avoid airborne deviations also work on the ground.
Pilots should also remain vigilant about vehicle/pedestrian
deviations (V/PDs). A vehicle or pedestrian deviation
includes pedestrians, vehicles or other objects interfering
with aircraft operations by entering or moving on the runway
movement area without authorization from air traffic control.
In serious instances, any ground deviation (PD or VPD) can
result in a runway incursion. Best practices in preventing
ground deviations can be found in the following section
under runway incursion avoidance.
Runway Incursion Avoidance
A runway incursion is “any occurrence in the airport runway
environment involving an aircraft, vehicle, person, or object
on the ground that creates a collision hazard or results in a loss
of required separation with an aircraft taking off, intending
to take off, landing, or intending to land.” It is important
to give the same attention to operating on the surface as in
other phases of flights. Proper planning can prevent runway
incursions and the possibility of a ground collision. A pilot
should always be aware of the aircraft’s position on the
surface at all times and be aware of other aircraft and vehicle
operations on the airport. At times, towered airports can be
busy and taxi instructions complex. In this situation, it may
be advisable to write down taxi instructions. The following
are some practices to help prevent a runway incursion:
• Read back all runway crossing and/or hold instructions.
• Review airport layouts as part of preflight planning,
before descending to land and while taxiing, as
needed.
• Know airport signage.
• Review NOTAM for information on runway/taxiway
closures and construction areas.
• Request progressive taxi instructions from ATC when
unsure of the taxi route.
• Check for traffic before crossing any runway hold line
and before entering a taxiway.
• Turn on aircraft lights and the rotating beacon or strobe
lights while taxing.
• When landing, clear the active runway as soon as
possible, then wait for taxi instructions before further
movement.
• Study and use proper phraseology in order to
understand and respond to ground control instructions.
• Write down complex taxi instructions at unfamiliar
airports.
Approximately three runway incursions occur each day at
towered airports within the United States. The potential
that these numbers present for a catastrophic accident is
unacceptable. The following are examples of pilot deviations,
operational incidents (OI), and vehicle (driver) deviations
that may lead to runway incursions.
Figure 14-48. Heads-up, eyes outside.
Pilot Deviations:
• Crossing a runway hold marking without clearance
from ATC
• Taking off without clearance
• Landing without clearance
Operational Incidents (OI):
• Clearing an aircraft onto a runway while another
aircraft is landing on the same runway
• Issuing a takeoff clearance while the runway is
occupied by another aircraft or vehicle
Vehicle (Driver) Deviations:
• Crossing a runway hold marking without ATC
clearance
According to FAA data, approximately 65 percent of all
runway incursions are caused by pilots. Of the pilot runway
incursions, FAA data shows almost half of those incursions
are caused by GA pilots.
Causal Factors of Runway Incursions
Detailed investigations of runway incursions over the past
10 years have identified three major areas contributing to
these events:
• Failure to comply with ATC instructions
• Lack of airport familiarity
• Nonconformance with standard operating procedures
Clear, concise, and effective pilot/controller communication is
paramount to safe airport surface operations. You must fully
understand and comply with all ATC instructions. It is mandatory
to read back all runway “hold short” instructions verbatim.
Taxiing on an unfamiliar airport can be very challenging,
especially during hours of darkness or low visibility. A
request may be made for progressive taxi instructions which
include step by step taxi routing instructions. Ensure you
have a current airport diagram, remain “heads-up” with eyes
outside, and devote your entire attention to surface navigation
per ATC clearance. All checklists should be completed while
the aircraft is stopped. There is no place for non-essential
chatter or other activities while maintaining vigilance during
taxi. [Figure 14-48]
Runway Confusion
Runway confusion is a subset of runway incursions and
often results in you unintentionally taking off or landing on
a taxiway or wrong runway. Generally, you are unaware of
the mistake until after it has occurred.
In August 2006, the flight crew of a commercial regional jet
was cleared for takeoff on Runway 22 but mistakenly lined
up and departed on Runway 26, a much shorter runway. As
a result, the aircraft crashed off the end of the runway.
Causal Factors of Runway Confusion
There are three major factors that increase the risk of runway
confusion and can lead to a wrong runway departure:
• Airport complexity
• Close proximity of runway thresholds
• Joint use of a runway as a taxiway
Not only can airport complexity contribute to a runway
incursion; it can also play a significant role in runway
confusion. If you are operating at an unfamiliar airport and
need assistance in executing the taxi clearance, do not hesitate
to ask ATC for help. Always carry a current airport diagram
and trace or highlight your taxi route to the departure runway
prior to leaving the ramp.
If you are operating from an airport with runway thresholds
in close proximity to one another, exercise extreme caution
when taxiing onto the runway. Figure 14-49 shows a perfect
example of a taxiway leading to multiple runways that may
cause confusion. If departing on Runway 36, ensure that you
set your aircraft heading “bug” to 360°, and align your aircraft
to the runway heading to avoid departing from the wrong
runway. Before adding power, make one last instrument scan
to ensure the aircraft heading and runway heading are aligned.
Under certain circumstances, it may be necessary to
use a runway as a taxiway. For example, during airport
construction some taxiways may be closed requiring re-
routing of traffic onto runways. In other cases, departing
traffic may be required to back taxi on the runway in order
to utilize the full runway length.
36
Figure 14-49. Confusing runway/runway intersection.
Figure 14-50. A sound practice is to write down taxi instructions
from ATC.
Since inattention and confusion often are factors contributing to
runway incursion, it is important to remain extremely cautious
and maintain situational awareness (SA). When instructed to
use a runway as a taxiway, do not become confused and take
off on the runway you are using as a taxiway.
ATC Instructions
Title 14 of the Code of Federal Regulations (14 CFR) part
91, section 91.123 requires you to follow all ATC clearances
and instructions. Request clarification if you are unsure of the
clearance or instruction to be followed. If you are unfamiliar
with the airport or unsure of a taxi route, ask ATC for a
“progressive taxi.” Progressive taxi requires the controller
to provide step-by-step taxi instructions.
The final decision to act on ATC’s instruction rests with you.
If you cannot safely comply with any of ATC’s instructions,
inform them immediately by using the word “UNABLE.”
There is nothing wrong with telling a controller that you are
unable to safely comply with the clearance.
Another way to mitigate the risk of runway incursions is to
write down all taxi instructions as soon as they are received
from ATC. [Figure 14-50] It is also helpful to monitor ATC
clearances and instructions that are issued to other aircraft.
You should be especially vigilant if another aircraft has a
similar sounding call sign so there is no mistake about who
ATC is contacting or to whom they are giving instructions
and clearances.
Read back your complete ATC clearance with your aircraft
call sign. This gives ATC the opportunity to clarify any
misunderstandings and ensure that instructions were given to
the correct aircraft. If, at any time, there is uncertainty about
any ATC instructions or clearances, ask ATC to “say again”
or ask for progressive taxi instructions.
ATC Instructions—“Hold Short”
The most important sign and marking on the airport is the
hold sign and hold marking. These are located on a stub
taxiway leading directly to a runway. They depict the holding
position or the location where the aircraft is to stop so as not to
enter the runway environment. [Figure 14-51] For example,
Figure 14-52 shows the holding position sign and marking
for Runway 13 and Runway 31.
When ATC issues a “ hold short ” clearance, you are
expected to taxi up to, but not cross any part of the runway
holding marking. At a towered airport, runway hold
markings should never be crossed without explicit ATC
instructions. Do not enter a runway at a towered airport
unless instructions are given from ATC to cross, takeoff
from, or “line up and wait” on that specific runway.
ATC is required to obtain a read-back from the pilot of
all runway “ hold short ” instructions. Therefore, you
must read back the entire clearance and “ hold short ”
instruction, to include runway identifier and your call sign.