U.S. Department

of Transportation


Federal Aviation



Air Traffic


A Communication from the  Director of Air Traffic                        



Issue # 2002 - 4

September 2002                                                                                             

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In this Issue:
Weather:The Name of the Game
Extra Vigilance: Is there Such a Thing?
Winter Operations and Runway Incursions
I Have Some Good News and Some Bad News
A Seasonal Reminder about Braking Action Advisories and PIREPs
Just a Reminder
Forewarned is Forearmed
Forecasting the Icing Hazard
Points to Remember
You Really Ought to Know
Deicing on Boeing 737s
Phantom Controllers May Not Want to Wait for Halloween

How to Complicate Visual Separation
Diverting Traps




Weather: the Name of the Game

/*FTER/ 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 individuals.

·         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.

Rather than adding to safety and efficiency, these are examples of time wasted – dangerously.

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)


/*FTER/ 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.

Facility 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.

Where 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)

Extra Vigilance: Is There Such a Thing?

/*T/ 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 definitions.

During some 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 your instructions.

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 this possibility.

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)

Winter Operations and Runway Incursions

/ER*FT/ 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 surface conditions.

·         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 operations. (ATP-120)

I Have Some Good News and Some Bad News

/*FTER/ 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 decision. (ATP-120)

A Seasonal Reminder About Braking Action Advisories and PIREPs

/*FTER/ 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.

When braking 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 departing aircraft.

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."

Braking action 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)

Just a Reminder

/*FTER/ 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 required. (ATP‑120)

Forewarned is Forearmed

/*FTER/ 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.

Weather related 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)


/*FTER/ 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.

There are 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.

Because of 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 handling procedures.

The arrival of the winter season is a good time for all operational personnel to review PIREP procedures, especially those concerning icing. (ATP-120)

Forecasting the Icing Hazard

/TER*F/ 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.

Generally 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
-16 șC level have changed into ice crystals already, and at the -25 șC level, 99.9 percent of the droplets have changed to ice crystals. Therefore, we should expect occurrences of aircraft icing to be scarce at temperatures around -16 șC and essentially nil at -25 șC or colder.

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)

Points to Remember

/TER*F/ 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.

An area 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 expected icing.

Remember the following points:

·         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)

You Really Ought to Know

/*FTER/ 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.

Aircraft icing 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.

Cumuliform 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

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 especially difficult.

Rime Ice

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 appearance.

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.

Mixed 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.

Icing-related 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 fail.

Another 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. (ATP‑120)

Deicing on Boeing 737s

/*TER/ 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)

Phantom Controllers May Not Want to Wait for Halloween….

/*TEFR/ 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)




Example #1

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.

Example #2

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 the descent.

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 sight.

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…

Example #3

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.
    "Yeah? Well, I thought you were doing it!"
You could term this type of separation as "thoughtful" separation.
    "I thought I had separation."
    "I thought he was doing it."
When that is the case, nobody is providing separation.


During the 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!

N1234A requests 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.

1.       "Approved as requested"

2.       "Deviate as necessary"

3.       "Deviation to the west approved, proceed direct Cavenaugh when able"

4.       "Deviation to the west approved"

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.

Clearance 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!








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