Issue # 2002 - 6
ATC should provide the departing flight every opportunity to meet the EDCT. Ways to accomplish this are unique to each airport but might include actions such as assigning the flight a higher priority in the taxi queue or temporarily "parking" the aircraft on the ramp. (The latter example may be used at times when an aircraft must be moved from the gate for operational needs but may not be taxiing to meet the departure window.) If possible, additional traffic management initiatives should not be assigned to flights that are participating in a GDP. If airport or en route constraints will cause a flight to miss its departure window, the airport traffic control tower (ATCT) should request a revised EDCT from the Air Traffic Control System Command Center (ATCSCC) through the appropriate traffic management unit (TMU).
When it becomes apparent that a flight will not be able to depart the runway within the EDCT window and has not yet begun taxiing for departure, or is operating in a manner inconsistent with meeting the EDCT window, a revised EDCT may need to be assigned by the ATCSCC. The GDP can then be amended to reflect the updated flight information, thereby enabling an accurate and real time assessment of the GDP performance. Each individual flight, specifically as pertains to the compliance issue, has an impact on overall system efficiency.
All EDCTs are expected to be adhered to in order to ensure the integrity of the program. When a GDP is in place, all flights destined for the impacted airport should be assigned an EDCT. If that is not the case, the ATCT should contact the ATCSCC (through the appropriate TMU). An EDCT will be assigned by the ATCSCC and the equivalent departure window applies.
/*ETR/ This is an update to an article on the same subject published in the Winter 1999‑2000 edition of the Air Traffic Bulletin. The problem with Airbus aircraft making early turns at high altitude still exists. Airbus has designed its Flight Management System (FMS) in A‑319/320/321 and 330 aircraft to command shallow turns, a term the industry calls "smoothing." Specifically, when these Airbus aircraft require a turn greater than 70 degrees above flight level (FL)190, they will begin that turn as much as 15 to 20 miles from the fix. The shallow turn (a less‑than‑half-standard rate) will result in the aircraft flying by the fix no closer than 5 miles. Controllers should know that the Airbus aircraft FMS is in compliance for area navigation (RNAV) equipage. The design standard states that for lateral containment, "The track change for a fly-by-fix, which is part of a required navigation performance RNAV route or procedure, is assumed to be 120 degrees or less" at or below FL190 or 70 degrees above FL190. The problem occurs when the aircraft is above FL190 and the RNAV route has a turn greater than 70 degrees or the controller clears the aircraft to a waypoint above FL190 that results in a turn greater than 70 degrees.
This article is intended to inform controllers of the following information:
· Expect Airbus aircraft to turn early for turns at greater than 70 degrees of heading change above FL190.
· The lateral displacement of the parallel track and the distance from the fix at the turn point, above FL190, will exceed the ATC procedural 4-mile, semi‑route width. It is important to note that below FL180, there is a federal rule that defines published route widths; however, there is no rule to define route widths at or above FL180. Therefore Airbus aircraft are in compliance with Federal Aviation Administration specifications above FL180.
· Reestablishment on the centerline of the follow-on route may be greater than what is expected from other type aircraft.
· Early‑turn anticipation occurs on published arrival and departure procedures as well, if turns are greater than 70 degrees above FL190.
We recommend caution and constant diligence when Airbus aircraft are flying a route requiring a turn exceeding 70 degrees of heading change. If separation is needed, recommend an initial vector rather than clearing an aircraft to a fix where a turn of greater than 70 degrees is required.
To further mitigate the early‑turn problem, we have notified organizations that develop procedures and routes to avoid turns requiring greater than 70 degrees of heading change above FL180. Airbus operators have been asked to advise their crews of this early‑turn characteristic. We are further recommending, where current traffic flows and procedures require turns greater than 70 degrees, that computer navigation fixes (CNF) be strategically located to force Airbus aircraft to fly closer to the fix and desired track.
Note: CNFs are for aircraft FMS database use only, and are not used for ATC purposes.
Finally, we are continuing to work with the Airspace
and Rules Division, ATA-400; Flight Technologies and Procedures
Division, AFS 400; Avionic Systems Branch, AIR‑130; and FMS/ RNAV
Task Force to minimize the impact of high‑altitude early turns. (ATP‑104)
/*TER/ On November 16, 2000, an F-16 aircraft was involved in a midair collision with a Cessna 172 aircraft near Bradenton, FL. The F-16 was the second aircraft in a flight of two that was on a low‑altitude training mission. The collision occurred at about 2,000 feet mean sea level and both aircraft were destroyed. The pilot of the Cessna was killed; however, the F‑16 pilot was able to eject from his aircraft and suffered minor injuries. All three aircraft were operating under visual flight rules (VFR) at the time of the accident.
On September 7, 2000, an F-117 aircraft was involved in a near midair collision (NMAC) with a B-757 aircraft over Los Angeles, CA. The aircraft passed within .15 (point‑one‑five!) miles of each other with approximately 500 feet vertical separation. In this incident there were no aircraft damages or injuries.
What do these two events have in common? In both situations, the civilian aircraft were in communication with ATC; however, the military aircraft were operating under VFR without receiving flight following. In the first incident, the Cessna had departed an airport in Class C airspace and was being vectored out of the area. A traffic call had been given concerning the lead aircraft in the flight of two F‑16 aircraft; however, the controller did not see the primary target of the wingman. In the second incident, the controller did not see the VFR track of the F-117; therefore, no traffic call was issued. The B-757 responded to a traffic alert and collision avoidance system resolution advisory, descending approximately 300 feet, to avoid the potential collision.
In response to these incidents, the United States Air Force (USAF) amended its "General Flight Rules" to require pilots of USAF aircraft operating under VFR to request and utilize VFR radar traffic advisory services to the maximum extent practical.
FAAO 7110.65, Air Traffic Control, paragraph 2-1-1, ATC Service, states, in part, "The primary purpose of the ATC system is to prevent a collision between aircraft operating in the system and to organize and expedite the flow of traffic. In addition to its primary function, the ATC system has the capability to provide (with certain limitations) additional services. The ability to provide additional services is limited by many factors, such as the volume of traffic, frequency congestion, quality of radar, controller workload, higher priority duties, and the pure physical inability to scan and detect those situations that fall in this category. It is recognized that these services cannot be provided in cases in which the provision of services is precluded by the above factors. Consistent with the aforementioned conditions, air traffic controllers shall provide additional service procedures to the extent permitted by higher priority duties and other circumstances. The provision of additional services is not optional on the part of the controller, but rather is required when the work situation permits."
FAAO 7110.65, Air Traffic Control, paragraph 2-1-2, Duty Priority, provides air traffic controllers guidance in prioritizing situations that can occur during normal operations. Providing additional services, which includes traffic advisory services to aircraft operating under VFR, is also addressed in this paragraph.
With the rate of NMAC reports received concerning
VFR military operations outside of restricted areas and warning areas,
we need to provide this additional service to the maximum extent
practical. In the incident that resulted in a collision, the center
controller working the two F-16 aircraft did offer VFR flight following;
however, it was refused. In the future, we can expect a lot more
requests for VFR flight following from USAF aircraft. If they do not ask
for it, we should be offering this service, as the primary function of
the ATC system is to prevent a collision between aircraft operating in
the system. (ATP-120)
/*TER/ The intent of the small plus (+)
article in ATB 2002-3A was to provide clarification on the
procedures applicable to small + aircraft. Separation standards for
small + aircraft in FAAO 7110.65, Air Traffic Control, paragraph
5-5-4, Minima, are identical to separation standards for small aircraft.
However, where Class B airspace rules are involved, FAAO 7110.65,
Air Traffic Control, paragraph 7-9-3 and Appendix A, Note, require that
small + aircraft be treated like large turbine engine powered
aircraft, which means that to the extent practical, ATC should clear
small + aircraft to/from the primary airport using altitudes and
routes that avoid VFR corridors and airspace below the Class B airspace
FAAO 7110.65, Air Traffic Control, provides standard ATC
phraseology for providing ATC services. Phraseology is standardized in
part to reduce opportunities for confusion and misunderstanding between
air traffic controllers and pilots. To minimize chances for
misunderstanding instructions, we encourage air traffic controllers to
use standard ATC phraseology and to speak at reasonable rates when
communicating with all flight crews. (ATP‑120)
/*TEFR/ Winter is here! Take time to refresh
yourself with the reminders concerning winter weather operations
outlined in Air Traffic Bulletin 2002-4. You can obtain a copy of this
bulletin online at http://www.faa.gov/atpubs/atb/02-4.htm. (ATP‑120)
Strict adherence to specified cutoff dates will ensure that
aeronautical information is published on the desired effective date. (ATA-100)
* Denotes Change Notice (CN). NOTE: There is no CN for Alaskan procedures.
When a pilot reports an emergency situation that requires the flight to divert from its original course to another destination, the flight crew's workload will undoubtedly increase. On the other hand, when a flight wishes to change its destination, your workload may increase as well, even under normal circumstances. The following information is offered to help smooth the way for both of you.
When an emergency requires a change in destination, your job is to provide appropriate routing clearance to the new destination. You should be aware of the NAVAIDs within your airspace and their service limitations. Failure to take this into account can seriously increase workloads and stress for both you and the flight crew. VOR/DME/TACAN radio aids are classified in the following manner:
It is true that more and more aircraft are equipped with sophisticated navigation devices that make range/reception considerations less important. However, the nature of the emergency might affect the operation of such equipment or it may not be clear what navigation capability the aircraft actually has on board. Regardless, your providing an initial heading until the crew can take the aircraft to the NAVAID will be greatly appreciated even by crews of aircraft with state-of-the-art equipment on board. The advanced aircraft navigation systems need only the 3-letter identifier for the NAVAID and can direct the aircraft there even if it is beyond the NAVAID's service limitations. But the older model transport aircraft such as the DC‑9, B‑737‑200, some DC‑10s, and almost all general aviation aircraft may be equipped with only VOR receivers which are subject to range reception limitations.
An aircraft that requests a change in route or destination will not be able to receive the NAVAID's signal if the aircraft is outside of its service limitations. If the aircraft is not within the service limits of the VOR, then the pilot will not be able to receive a navigable signal and will not be able to fly to it. You should be aware of this and issue a radar vector for the aircraft to fly until it is able to receive a navigable signal. Another thing to keep in mind is that if the aircraft is above FL180, the pilot will be using high altitude en route charts for navigation. High altitude en route charts do not have the low altitude route structure and associated intersections and NAVAIDs depicted on them. So if you tell the pilot to proceed direct to Chumly VOR and it is not part of the high altitude route structure, the pilot will not be able to find it on the chart. During normal operations, such irritations may cause a slight delay while the pilot hunts up the information; or add to your frequency congestion by the pilot having to ask you for a heading or additional questions like, "What's its frequency?" or "How do you spell that?" and "What's the identifier for that?" During an emergency, it adds to the stress that the crew is under and increases your workload exponentially.
At a minimum, issue a radar vector for the aircraft to fly until its own navigation resources can take over. Include the 3-letter identification for the NAVAID that you are asking the aircraft to fly toward. If you suspect that the aircraft may be using VOR only equipment, provide the frequency as well. These simple gestures not only help the crew but it also helps you because it cuts down on the additional questions the crew might have to ask, thus reducing the airtime congestion and getting the aircraft on its way as quickly as possible.
Be prepared to provide additional information to the emergency aircraft. If asked, you can inform them of suitable airports that are closer that they might choose. Once a choice is made, provide basic information such as runway in use, approach to expect, wind direction and velocity, and runway length. This will help the crew plan and manage their aircraft. If you have provided clear instructions regarding route and altitude and pre-approach information, the crew will busy themselves with managing their aircraft rather than managing to busy you.
When a serious accident or incident occurs on or near the airport, ATC often has the most current and accurate information regarding the aircraft's position. Rescue personnel will rely upon ATC to guide them to the site in order to rescue the survivors. Obviously, the quicker the rescue personnel can reach the accident site, the better the chances the wounded have of surviving. It should be equally obvious that information regarding the location of the accident site must be as accurate as possible and unambiguous.
There have been instances where the position of the accident site is not clearly rendered to the aircraft rescue and firefighting (ARFF) personnel, and precious moments may be expended while searching in the wrong area or doubling back to get to the site. The two following examples illustrate how imprecise language can mislead rescue personnel. Your ability to provide accurate information in an emergency situation is a moment where you can really help.
If you said you would look for the aircraft in the river, then you made a logical assumption but you would not find the aircraft. (No, it did not sink!) If you said that you would look for the aircraft in the tidal basin, you made a lucky guess and would have found the pilot and passengers struggling out of the aircraft.
The information was not really clear, because the aircraft could have come down immediately after takeoff into the river, or (as it did in this case) it could have managed to stay aloft long enough to come down into a pond or pool closer to the runway's approach end. What really happened? The rescue personnel first went to the river to look for the aircraft while the occupants were struggling to get out of the aircraft that had ended up in the pond at the other end of the airport!
Ambiguous statements have more than one meaning. What you say can mislead as easily as it can help if you are not careful. The statement that the aircraft crashed into the water after it departed runway 8 is wide open to interpretation because it is not specific.
Many airports have a grid system that can be used to better describe where the aircraft is located. In absence of the grid system, direction from the airport expressed in magnetic compass points is excellent. Before we discuss this point, take a look at example #2.
Where is the end of runway 27? Is it at the departure end, or is it at the approach end? Is it at the end where the numeral "27" is, or is it at the end where the numeral "09" is? In conditions where rain, fog, or snow obscure visibility, even though the aircraft may be burning, rescue personnel may not be able to see it until they get very close to it. Your directions can be critical for a quick arrival. In this example, the rescue personnel went to the approach end of the runway and, finding nothing there, began a methodical sweep down the runway before finding the wrecked aircraft well off the departure end.
Since the controller could not actually see the aircraft either, it was unknown whether the aircraft was still on the runway or off its end or sides. The controller might have stated that the aircraft had landed on runway 27 and was last seen mid-field. This tells the listener that the aircraft is not on the first half of the runway and to look for it somewhere along its length on the last half. If it is known that the aircraft is off the end of the runway, the controller should say that the aircraft is off the departure end of runway 27, or that it is at the west end of runway 27.
Use clear language to convey your message: "The aircraft is 300 yards west of the wind sock,"; "The aircraft is ¼ mile west of runway 27"; "The aircraft was last seen descending into the approach lights for runway 27, ¾ of a mile east of the airport"; "The aircraft was last seen 3 miles north of the airport descending southbound behind a line of trees"; "The aircraft is located in sector 15."
Avoid the vague statement such as: "The aircraft is past the windsock."; "* * * was last seen descending into the approach lights"; "* * * was at the end of runway 36"; "* * * was last seen on downwind descending behind trees." Too much is left to guess and interpretation in these last examples because it is assumed that the meaning is clear. The ARFF crew does not necessarily know at any given moment what runway or approach you were using at the time of the accident, and if you cannot help them by pinpointing the area where the aircraft was last observed, they must use up precious time sweeping a larger area.
If the airport management has provided your facility with a grid system, use it to advantage. "The aircraft is in sector 8" is infinitely better than the less precise description, "The aircraft is 2 miles north of the airport." Try to be as accurate as you can. The example, "The aircraft is ¼ mile east of runway 8" is much more precise than is, "The aircraft is east of the runway/airport." We are not suggesting that you should get bogged down with estimating mileage, but we are suggesting that you strive to be as clear, and precise as you can. Remember that vague directions are open to the wrong interpretation so choose your words wisely.
The traffic alert and collision avoidance system (TCAS II) has proven to be an effective airborne collision avoidance system for the most part. I say for the most part because there are occasions where the system provides an alert to the pilot when no hazard exists. An example of this is the "bump up syndrome" that can occur when one aircraft is descending to an altitude 1,000 feet above the altitude that another aircraft is level at or climbing to. The high rate of descent or climb and proximity of the aircraft can still trigger a false alarm to which the pilot will respond. Since the early 1990s when TCAS was first introduced into the air traffic system, several software changes have been incorporated that have corrected the majority of circumstances where a false resolution advisory (RA) is signaled to the pilot. Part of the solution has been to allow the aircraft to get closer before the RA is issued to the pilot, thus eliminating the majority of the "bump up" false alarms. Therefore, it is very important that pilots follow the RA indications exactly and promptly to avoid close encounters of the worst kind. Even more important, controllers must understand that once the pilot has received an RA, it is crucial that the controller does not countermand the RA. Instructions contrary to the RA will result in a closer encounter at best and fatal results at worst.
In all cases that we are aware of to date where the pilot has decided to ignore the RA, or decided to follow the controller's directions instead of the TCAS instructions, the aircraft have gotten very close together. In Europe, a Swiss controller instructed a Russian aircraft over Badensee, to descend to avoid another aircraft and the crew elected to obey the controller's instructions instead of following their TCAS RA to climb. The aircraft collided with a B-757 that was following a TCAS RA to descend, killing all aboard both aircraft. In the United States, we are aware of at least four fairly recent events where either the pilot decided to disregard the RA and/or the controller continued to insist that the aircraft climb/descend contrary to what the TCAS required. In all cases, the aircraft came closer to each other than they would have had the RA been followed. On rare occasions, such as the Badensee midair collision, the controller's countermanding the TCAS RA, coupled with the timing and degree of the crew's response contrary to the TCAS RA, terrible results can occur.
FAAO 7110.65, Air Traffic Control, paragraph 2-1-27, TCAS Resolution Advisories, states, "When an aircraft under your control jurisdiction informs you that it is responding to a TCAS Resolution Advisory (RA), do not issue control instructions that are contrary to the RA procedure that a crew member has advised you that they are executing." The key element in this requirement is knowledge. If you know that the aircraft is following a TCAS RA, think "hands off!" Do not do anything other than provide traffic information to the aircraft. Do not instruct the aircraft to do anything else until the TCAS RA is over. The TCAS equipment gets updates on the other aircraft's position every second, while your equipment gives you updates every 4.5 to 12 seconds depending upon your radar update system. The TCAS projects where the aircraft will be in future, and will provide the pilot with instructions that will place both aircraft at a safe distance from each other. Standard separation will be lost, but the aircraft will not collide. If both aircraft are equipped with TCAS, the units will coordinate their movements with each other so that they will not both be given the same RA direction. The TCAS equipment can communicate with as many as five other aircraft simultaneously, so you should not worry that the aircraft will climb/descend into another aircraft. However, TCAS will not be able to detect an aircraft that does not have an operating Mode C transponder.
TCAS is not the end-all answer to collision prevention. The air traffic system still depends upon the pilot's responsibility to see and avoid other aircraft in visual flight conditions and on the controller for clearances that ensure standard separation is maintained. Ideally, the system would never see a TCAS RA; however, it is good to have a safety net of sorts in place to help out when other methods fail. The controller's part in the system is to maintain the separation standard, and if that happens to fail, then to recognize when to let go and let the TCAS do its work. (AAT-20)