Issue # 2002 - 4
Let us start on a serious note by stating that our business is no game.
However, if we were to use the phrase, "the name of the game,"
the name of our game could very well be communications. It has been said
that an efficient air traffic control system requires timely and
accurate communications between all concerned. The word
"requires" is probably not a strong enough word. The word
"demands" would seem more accurate. Many, if not all, of the
functions we perform in air traffic depend directly on timely and
accurate communications. It is an obvious understatement to say that the
information we exchange is often critical.
We must also
remember the importance of complete communications between
Coordination that is not complete
is not coordination.
Control instructions that are not
complete do not control.
A clearance that does not ensure
separation is not a complete clearance.
A briefing that does not convey
complete information is not a briefing.
Each of these
examples is meant to illustrate the dangers that present themselves when
our one‑on‑one communications are not complete.
adding to safety and efficiency, these are examples of time wasted
The need for
complete and accurate communications in our business is obvious, not
just during the winter, but all year round. However, during the winter,
like other adverse weather periods, there is usually more information to
convey. Let us all remember not to overlook the obvious. Let us also
make certain that all of our communications are complete. (ATP-120)
Good planning can go a long way toward minimizing the impact of winter
weather. If it has not been done, now is the time to review and update
all of the local directives that specifically relate to winter
operations. Establish contacts and procedures for coordination with
airport operators and users to ensure everyone knows the procedures for
snow removal and runway condition reporting.
managers should participate on airport snow committees; however, only in
an advisory capacity. Remember that Federal Aviation Administration
personnel are not the decisionmakers on the condition of the runway or
whether the airport should be closed because of weather. The airport
management must make these decisions.
appropriate, managers should discuss gate hold procedures that may be
implemented during the winter. Ensure that there is a clear
understanding of how and when these procedures apply. (ATP-120)
The word "vigilance" is defined in Webster's New World
Dictionary as "the quality or state of being vigilant;
watchfulness." This definition of vigilant also includes the words
"characterized by vigilance or wakefulness; especially alert to
danger; watchful." The word "watchful" is defined as
"vigilant; alert; attentive; closely observant." End of
English lesson, but the message here is more important than simple word
winter operations such as snow removal, there is a need for extra
vigilance. Snow removal at some locations is accomplished by contractors
who may know little about airport operations. Consequently, they may be
unaware of certain hazards inherent to airport operation. This potential
for danger must be recognized, and the need for positive control cannot
be over emphasized.
Following are a
few suggestions to help you stay out of winter operations trouble:
Do not base runway separation on an
assumption that a truck driver or snowplow operator has the same
understanding of control instructions as a pilot. Phrases and words in
common use by us such as, "hold short," "expedite
departure," and "proceed across"
may sound like a foreign language to someone else.
Keep in mind the visibility you
have from the tower may be different from that of the snow crew. Removal
operations such as plowing, sweeping, and snow blowing can reduce
visibility to near zero-zero in the immediate area. Make sure that any
visual reference you use in your instructions is something that you both
can see. Just as important, make sure that you and the equipment
operators are looking at the same reference.
Remember that the noise level
inside of a snow removal machine may be high. Make sure that your
microphone technique enhances positive communications.
Runway contaminants, snow, and ice
in particular, are slippery. You can provide a margin of safety by
giving ground equipment operations a reasonable distance to comply with
Know the parts
of the winter operations plan that apply to your operations. These are
normally contained in facility directives. Remember that, given a
chance, any communications can be misunderstood. Do not contribute to
Last, and most
importantly, know the provisions of FAAO 7110.65, Air Traffic Control,
Chapter 3, Section 1, which contains procedures applicable to
ground operations. (ATP-120)
Several factors that occur during the winter months deserve our
attention in our quest to further reduce runway incursions. Personnel at
stations that provide an Airport Advisory Service (AAS), as well as
those in towers, should keep the following factors in mind:
Snow removal vehicle operation on
runways and other movement areas.
Aircraft taxiing slower because of
Aircraft needing and using more
time to exit or cross runways because of surface conditions.
Various forms of precipitation
reducing controller and pilot visibility.
Plowed snowdrifts causing blind
spots for taxiing aircraft.
Glare caused by bright sunlight
reflecting off of snow (and ice) on the ground.
These are just
a few of the important items we must consider as we approach winter
Do not keep operational information to yourself. Whether it be good news
or bad news, share the wealth (or the grief) with everyone who has an
operational need. To be useful, up‑to-date information on both
weather and field conditions must be in the hands of those who need it.
If, as a
controller, you see that you are going to have to restrict traffic,
relay that information up and down the line as soon as you can. Do not
surprise the adjacent sector at handoff time. Of course, the other side
of this coin is that when restrictions are no longer needed, do your
part to get them lifted.
As a briefer,
make sure you give complete information to each of the pilots based on
their requests. Items such as freezing level and, of course, reports and
forecasts of icing take on an added meaning this time of the year. The
type of delivery may vary with each individual pilot, but the final
product does not. Each contact with a pilot should result in enough
information being conveyed so that the pilot can make an intelligent
Runway braking action reports are furnished by the pilot or airport
management. These reports require categorization using the terms
"good," "fair," "poor," "nil,"
or a combination of these terms.
action advisories are in effect and the braking action report affects
only a portion of a runway, describe the braking action for that portion
of the runway and issue it in descriptive terms to each arriving and
When the report
includes the terms "poor" or "nil," or whenever
conditions are conducive to deteriorating or rapidly changing runway
conditions, terminal facilities are required to broadcast on the
Automatic Terminal Information System the statement, "Braking
action advisories are in effect."
pilot weather reports (PIREP) should be solicited when braking action
advisories are in effect or when requested. PIREPs should be solicited
far enough in advance to allow the pilot time to adequately evaluate the
situation and render a meaningful braking action report.
Remember, it is
not only our responsibility to solicit these reports when required, but
also to issue this information in time for it to be useful to the pilot.
Procedures concerning this subject are in FAAO 7110.65, Air Traffic
Control, Paragraphs 3-3-3, 3-3-4, and
3-3-5, and FAAO 7110.10, Flight Services, Paragraphs 4-6-6
and 14-1-21. (ATP-120)
Portions of Federal Aviation Regulations 91 and 135 prohibit visual
flight rules flights into areas of known light icing under some
conditions. In addition, some military aircraft are extremely sensitive
to airframe icing of any degree. Therefore, it is important that all
icing reports from pilots be processed in accordance with established
procedures. Soliciting and relaying PIREPs of light icing are also
The thought that we have been trying to convey throughout this document
is the importance of communications. While the focus of this issue is
winter operations, there really is not anything special about winter
operations. Certainly, snow and ice on the ground are unlikely in the
warmer months, but hazardous weather conditions of one kind or another
are not unique.
information such as PIREPs, significant meteorological information (SIGMET),
meteorological impact statements, central weather advisories, and other
advisories always require special attention and handling. This
information will always be an important factor that pilots must
consider. No matter what time of year, timely action is important.
Do not be
fooled into thinking that winter weather replaces hazards that exist
during the rest of the year. Icing, turbulence, low‑level wind
shear, restricted visibility, and even thunderstorms can, and do, exist
during the winter season. (ATP-120)
Aircraft icing is one of the hazards we have been talking about that can
be with us all year round, but gets extra attention during the winter.
Ice, including frost, can be a hazard because of the way it affects
airframes and power plants. Accumulations of ice on the outside of
aircraft impair wing lift and propeller thrust. Ice can reduce engine
performance to dangerous levels. In the most severe cases, it can cause
engine failure. The double danger is that while lift and power are being
reduced, that same icing is increasing the weight of the aircraft a
deadly vicious circle.
several forecasts that contain warnings of icing. However, PIREPs are
the only source of actual icing reports. PIREPs regarding icing are more
than just nice‑to‑know information.
their importance, procedures for soliciting PIREPs are contained in FAAO
7110.65, Air Traffic Control, Paragraph 2-6-3,
and FAAO 7110.10, Flight Services, Paragraphs 9-2-5 and 9-2-9. The
briefing and broadcast paragraphs of these directives also contain PIREP
The arrival of
the winter season is a good time for all operational personnel to review
PIREP procedures, especially those concerning icing. (ATP-120)
What do meteorologists at the National Aviation Weather Advisory Unit (NAWAU)
look at when trying to determine if an icing hazard exists? How do they
determine where the hazard will be during the valid time of the upcoming
area aviation forecast?
In a nutshell,
NAWAU meteorologists try to determine where there will be enough
moisture to form clouds above the freezing level. If they look at the
moisture too far above the freezing level, they find they are tracking
ice crystals instead of liquid water droplets.
This brings up
an important question. Why is there liquid water above the freezing
level? Liquid cloud droplets in an environment of rising air can rise a
substantial distance above the freezing level, becoming colder and
colder, without freezing as long as they remain undisturbed. What is
meant by "undisturbed?" If an airplane would happen to fly
through these "supercooled" cloud droplets, the droplets would
most likely freeze on impact with the aircraft. The smaller drops would
freeze instantly into rime ice. If the clouds happened to be made up of
larger drops, it might take a few seconds for the drops to freeze into a
glaze of clear ice.
speaking, the stronger the upward motion of the droplets within the
cloud, the greater the vertical distance droplets will rise before
changing into ice crystals. However, meteorologists studying clouds have
learned that 95 percent of the cloud droplets at the
In addition to
forecasting the horizontal and vertical extent of cloud formations above
the freezing level, NAWAU meteorologists must determine which cloud
areas will most likely contain significant amounts of supercooled water
droplets during a specific 12- to 18-hour period. Needless to say, this
is not an easy task. (ATP-120)
Base your advice to pilots concerning icing on forecasts and PIREPs.
Forecasts delineate general areas of icing potential; PIREPs pinpoint
actual encounters. In using PIREPs, remember that conflicting reports of
type or intensity may be due to different types of aircraft. By piecing
together several reports, you frequently can get a more comprehensive
picture of icing potential.
forecast always contains a section on icing. It specifies freezing
levels, expected changes in freezing level, and altitudes where icing is
most likely. SIGMET and airmen's meteorological information are also
excellent sources of icing information. Always pass on any icing reports
to the forecaster, and do not hesitate to ask for his/her help when
needed. He/she is in an excellent position to integrate pilot reports
and the latest analyses and observations into a current picture of
In stratiform clouds, rime icing
may be very extensive horizontally. An altitude change of the aircraft
to either a flight level with above‑freezing temperatures or a
flight level colder than -5 șC likely will alleviate icing conditions.
An altitude change also may take the flight out of clouds.
In cumuliform clouds, clear ice
usually is encountered with brief, heavy accumulations from 0 șC to -10
șC, and lesser amounts at lower temperatures. Any flight path change to
get out of the clouds and into visual conditions is in order.
In freezing rain due to frontal
overrunning, a climb into the warmer air aloft is in order. Above‑freezing
temperatures may be found at a lower level in some cases; and then,
terrain must be considered.
Many small aircraft do not have
deicing equipment, especially those based in warm climates. Never assume
that an aircraft has deicing equipment.
During icing or potential icing
conditions, PIREPs are especially valuable to the entire aviation
community and should be collected and transmitted into the system.
Ground icing, frost, and carburetor
icing are generally considered operational problems. However, you can
sometimes alert a pilot to ground icing or frost potential when you know
conditions are favorable. (ATP-120)
As aviation professionals, we must all be knowledgeable about the basic
conditions which are most likely to produce winter flying problems. It
does not take much time for a problem in the cockpit to become a problem
in the air traffic facility.
can occur either in the air or on the ground. A common condition for
icing is when an aircraft taxis through slush or water at or near
freezing level. It can also occur when aircraft fly through
precipitation and the air temperature is near or below freezing level.
The most severe icing occurs with a free air temperature between 0 and
-10 șC. However, icing is not uncommon at much colder temperatures, all
the way down to -40 șC.
clouds are more likely to produce serious ice formation than other
clouds, particularly if freezing rain is present. However, at altitudes
above the freezing level, any layer of air with a narrow temperature dew
point spread is a potential icing zone. Remember, ice can form by
sublimation: water going directly from its gaseous state to the solid
state; in this case, going directly from water vapor (always present in
the atmosphere) to solid ice. Types of aircraft icing include clear,
rime, and mixed.
Clear ice forms
when, after initial impact, the remaining liquid portion of the water
drop flows out over the aircraft surface, gradually freezing as a smooth
sheet of solid ice. This type of icing forms when drops are large as in
rain or in cumuliform clouds.
Clear ice is
hard, heavy, and tenacious. Its removal by deicing equipment is
Rime ice forms
when water drops are small, such as those in stratified clouds or light
drizzle. The liquid portion remaining after initial impact freezes
rapidly before the drop has time to spread over the aircraft surface.
The small frozen droplets trap air between them giving the ice a white
Rime ice is
lighter in weight than clear ice and its weight is of little
significance. However, its irregular shape and rough surface make it
very effective in decreasing aerodynamic efficiency of airfoils, thus
reducing lift and increasing drag. Rime ice is brittle and more easily
removed than clear ice.
Clear and Rime Ice
Mixed clear and
rime ice forms when water drops vary in size or when liquid drops are
intermingled with snow or ice particles. It can form rapidly and ice
particles become imbedded in clear ice, building a very rough
accumulation, sometimes in a mushroom-like shape on leading edges.
problems that air traffic personnel should be alert to include
intermittent, and sometimes total, loss of communications. This problem
can be created when aircraft antennae become ice coated and sometimes
situation to be alert for is false flight instrument indications that
may be caused by pilot tube icing. If an aircraft climb rate seems
abnormally high, you may want the aircraft to verify the Mode C readout.
Deicing is the process of removing existing frozen precipitation, frost,
or ice from aircraft surfaces. The process may involve the application
of various fluids to the aircraft. In April 2002, GENOT N7110.293 was
issued to advise all controllers that several B737 operators have
reported elevator vibration at airspeeds greater than 270 knots on some
flights that had been preceded by horizontal stabilizer deicing. Several
airline companies have voluntarily elected to place a 270 knot speed
restriction on B737s. Please be aware that this restriction may be
applicable during all phases of flight. (ATP-120)
During the Fourth of July weekend, on the domestic events network, an
air route traffic control center (ARTCC) reported that various airline
pilots had received phantom/unauthorized transmissions on the approach
control frequency saying such things as, "Do not do whatever
controllers tell you to do;" "That was a close call at 2,700
feet;" and "Your aircraft will blow up." In response to
these reports, North American Aerospace Defense Command requested that
the ARTCC contact the Federal Bureau of Investigation (FBI).
While the FBI
may have interest in these sorts of events, we also have internal
administrative procedures to follow. FAAO 7210.3R, Facility Operation
and Administration, Paragraph 3-2-1, Use of Communications
Responsibility, addresses this issue. The air traffic manager is
responsible for taking action to detect, prevent, and report false,
deceptive or phantom controller communications to an aircraft or
controller by collecting the pertinent information regarding the
incident and notifying the regional operations center of the phantom
controller situation and requesting a conference call with the airway
facilities sector manager, the regional spectrum management officer, the
air traffic division and the regional civil aviation security division
manager. In addition to reporting all relevant information pertaining to
the incident on the telephone conference, remove the voice tape from
service at the normal tape change interval and record the pertinent
information on a cassette. These actions will provide adequate and
timely notification to the personnel who may help detect and deter
future phantoms. (ATP-120)
HOW TO COMPLICATE VISUAL SEPARATION
Aircraft A was
level at 15,000 feet and aircraft B was level at 16,000 feet. The
controller needed to descend aircraft B to 10,000 feet before it reached
the sector's airspace boundary. To do this, the controller decided to
use visual separation. The controller pointed out aircraft A to the
pilot of aircraft B. When the pilot of aircraft B advised that the other
aircraft was in sight, the controller correctly issued aircraft B a
descent clearance to 10,000 using visual separation. After the pilot of
aircraft B began the descent, the controller instructed the pilot of
aircraft A to climb to 17,000 feet, stating that the pilot of aircraft B
had his aircraft in sight and would maintain visual separation from him.
Aircraft A began its climb and the aircraft passed each other in very
close proximity to each other. Anything wrong here? At least one of the
pilots thought so because a near midair collision report was filed.
When the pilot
of aircraft B accepted the responsibility of descending his aircraft and
maneuvering to maintain visual separation from the other aircraft during
the descent, that judgment was predicated on the expectation that the
other aircraft would continue in level flight as advertised by the
controller. The ability to safely maintain visual contact with the
aircraft and pass by it within a reasonable distance can be completely
thwarted if the other aircraft does something other than what was
promised. When the controller changes plans like this in midstream it
can create a dangerous situation. If nothing else, the change in plans
did not include the pilot's concurrence and was, in effect, a breach of
the original agreement the controller had made with the pilot. Take care
to avoid such surprises.
Aircraft A was
westbound, level at 12,000 feet. Aircraft B was also westbound, level at
13,000 feet. Aircraft B was faster than, and steadily overtaking
aircraft A. The controller pointed out aircraft A to the pilot of
aircraft B and then told the pilot to maintain visual separation from
aircraft A while descending to 10,000 feet. The pilot agreed and began
There is a
problem with this scenario. As aircraft B
descends, visual separation will be maintained only as long as
the pilot can see aircraft A. But as soon as aircraft B passes the other
aircraft, it will no longer be able to see its traffic. (Few aircraft
have rearview mirrors!) If this happens when vertical or lateral
separation is not yet in place, the controller will have lost
separation. If the pilot can change altitude and keep the other aircraft
in sight until vertical or lateral separation is again in place, visual
separation will have correctly been used.
The worst case
might be the same situation with a smaller speed differential where one
aircraft passes the other but does not pull away. Instead, it gets
slightly in front of the other aircraft and stays there as it descends.
Lateral separation is never gained and thus standard separation is not
obtained until the aircraft reaches or passes through an altitude 1,000
feet below the other aircraft. Visual separation ceases to be in place
as soon as the pilot loses the ability to keep the other aircraft in
You could be
clever and point out the passing aircraft to the pilot being passed and
instruct that pilot to maintain visual separation from the aircraft that
is passing. Of course if the pilot refuses the clearance or cannot
visually locate the passing aircraft, separation will be lost if the
passing aircraft does not get to a position where it is either laterally
or vertically separated before losing sight of the aircraft it was
passing. A word to the wise
One of the most
common mistakes made with visual separation is when the controller fails
to issue the pilot the clearance
to maintain visual separation. Traffic is issued to both aircraft, the
pilot agrees that visual separation can be maintained, but the
controller does not issue clearance to "maintain visual
separation". After the fact, when the pilot is interviewed, the
pilot may state that he/she was maintaining visual separation from the
other aircraft. If that were so, why then, would the incident still be
considered as a separation loss?
There must be
no question that separation was in place,
how it was being provided, and who was providing it.
After-the-fact discovery that separation was in place is useless. It is
nice to find out that the pilot was providing the separation after all,
but finding that out later is unacceptable. Never assume that just
because the pilot said that he/she could
provide the visual separation, that separation was
being provided without an explicit clearance to do so. What generally
happens in that case is the old, "I thought you
were doing it!" scenario.
summer months in particular, thunderstorms
and large buildups of cumulonimbus clouds are common. They can be
pretty to look at, a welcome harbinger of rain for thirsty crops,
ominous, or a threat of flooding for rain weary areas. Pilots consider
the thunderstorm more of a threat to air safety and comfort than crop
relief, and will take great pains to avoid an encounter with one. The
thunderstorm can destroy aircraft, cause loss of control with subsequent
destruction, or provide a really terrifying ride. And as any experienced
controller knows, when there are thunderstorms in the area, pilots will
ask to deviate away from or around them and the controller's workload
can skyrocket. It can seem like trying to control flies in a bottle!
Aircraft are going everywhere but where you want them to go! The
diverting-around-bad-weather scenario can be managed as long as you do
not fall into a simple trap. The trap is akin to opening the jar and
assuming that the flies will stay inside!
to "deviate, there are build-ups in the area." You can respond
in one of several ways, but each has a consequence of which you must be
aware. All four are acceptable clearances, but you must realize what and
how much you are approving when you use them.
"Approved as requested"
"Deviate as necessary"
"Deviation to the west
approved, proceed direct Cavenaugh when able"
"Deviation to the west
The first two
clearances may be interpreted by the pilot to include altitude changes
as well as lateral movements of varying degrees. "Approved as
requested" works only when what the pilot actually said is
"A-OK" with you. In our example, the pilot does not mention
direction, only that there are buildups in the area and the desire to
deviate. Do not assume deviate means lateral movement only. If it does
matter, be sure to specify in your reply that deviation is for lateral
movement only. If it does not matter that the pilot moves laterally and
vertically to avoid the buildups, the first two clearances are an
appropriate response to the pilot's request. However, if things change,
you must remember to modify those clearances as needed because....
Woe to the
controller who assumes
that the pilot presently on a particular heading will stay on
that heading or course. Woe to the controller who assumes
that the aircraft will stay at its last assigned altitude. The
"deviate as necessary" clearance opens the door wide for the
pilot to do just about anything.
The clearance "approved as requested" is risky if the pilot
says something like "We've got some stuff building out here and
need to deviate." The pilot did not specify whether the deviation
would be vertical, lateral, or both in nature. If you do not specify
either, the lid is off the jar and the flies will be out! Make sure you
understand what the pilot is asking to do. What you say when you respond
to the pilot's request is very important. If you intend for the pilot to
only go in one direction, say so. Be specific about what you expect. Do
not leave it up to the pilot to interpret.
Sometimes it is appropriate to use an open door (or jar) clearance. Just
remember to shut the door and restrict the deviating aircraft to a
heading, altitude or direction of travel if you want to use the airspace
in the vicinity where the aircraft is operating at will. Do not make the
mistake of assuming what the aircraft will do as did a luckless
controller recently. An aircraft on a westbound heading had been given
the go-ahead to deviate north of course and proceed on course when able.
The aircraft had moved north of its course and had been on a
northwesterly heading for a while and the controller assumed that the
aircraft would continue that course. The controller issued a descent
clearance to an eastbound aircraft whose course would bring it eastbound
7 miles south of the deviating aircraft's present course. Naturally, the
northwesterly aircraft chose an inopportune moment to turn south to
proceed on its original course and separation was lost.
responses #3 and #4 (above) clearly refer to lateral movement only, but
the controller must realize that how far and how many movements may be
made may differ widely from what he/she expects. Prevent surprises and:
Issue a specific clearance or
Go back to the aircraft and put a
restriction on its movement before issuing a clearance to another aircraft that will bring
it into the vicinity of the deviating aircraft's possible path.
Do not assume what the pilot will
do, make sure!