MANAGEMENT OF HOLDING PATTERNS: A POTENTIAL ADS-B APPLICATION

Arthur P. Smith, Hilton Bateman, The MITRE Corporation, McLean, VA

Abstract Holding in the National Airspace System

(NAS) is a necessity in the management of air traffic into the major airports in the system. The necessity follows from the desire not to waste any landing slots at the airport in the face of system uncertainties. Holding patterns maintain a ready reservoir of aircraft nearby the airport to provide a steady flow of aircraft. At the same time that this strategy provides an effective mechanism for providing pressure on the airport, it is workload intensive and inefficient in flowing aircraft uniformly to the airport.

This document provides evidence of the amount of holding that is experienced for the New York airports and introduces a concept of using Automatic Dependent Surveillance – Broadcast (ADS-B) information to reduce the controller workload and increase the uniformity of the flow of aircraft out of the holding patterns. Estimates of the expected benefits are also presented as well as the next steps to be taken.

Background In a system as dynamic as the U.S. National

Airspace System (NAS), provisions need to be made for accommodating unexpected disturbances in the system (e.g., severe weather events) while still minimizing the underutilization of system resources (e.g., unnecessarily large gaps in the arrival stream to an airport). One of those provisions is the use of aircraft holding at pre-designated locations. For instance, if an airport is negatively impacted by weather or congestion, aircraft can be placed in holding patterns and metered to exit the holding patterns as conditions permit. These holding patterns allow controllers to react to a situation while at the same time provide a mechanism to place as much “pressure” on the system resources as can be tolerated.

However, the capacity of a holding pattern is finite. This means that controllers have to manage

one or more holding patterns which results in additional workload. If some of this workload could be shared with the pilots through an ADS-B application, the controller workload could be reduced. An additional benefit could be that the metering of the aircraft out of the holding pattern will be more uniform and hence the throughput of the system will be increased.

The Problem

Basic Management of Holding Patterns A well managed holding pattern at or near the

initial approach fixes of an airport will keep constant pressure at the runway regardless of acceptance rate. This is probably the most efficient means of keeping arrival pressure on the airport. Since control of the NAS has not reached the stage of precisely and accurately planning the trajectories of all aircraft, the necessity of holding patterns may be with us for a long time.

However, holding is one of the most complicated tasks that a controller must perform.

Awareness of the effects of the holding pattern within one’s airspace must always be maintained from the time the holding pattern is activated. Decisions of altitude usage, holding speed, entry maneuvers, holding positions, and holding length must all be made prior to an aircraft entering a holding pattern. Holding, once decided upon, becomes the focus of the controller team. If only one person is present at a sector then it is generally FAA policy to add additional staffing to the holding sector because of the increased workload and because of the increased possibility of an operational error.

Holding using published patterns is straightforward, requiring the least phraseology of all holding scenarios. (See paragraph 4-6-1 in [1]) This is usually applicable at the fixes closest to the airports. However, as holding patterns fill (this varies depending on the airspace) and as patterns

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are filled further upstream, holding may be initiated requiring much longer, full clearances. This is very labor intensive. (See paragraph 4-6-4 in [1]). In all cases the issuance and updating of EFC (Expect Further Clearance) times are required. Additionally a requirement exists for the controller to inform the pilot of the reasons for the delay. This information may or may not be transmitted to the pilot depending on the controller’s workload.

It is generally the case that holding patterns are entered from the top and exited from the bottom, but this does not always happen. In this paradigm the controller is continually separating the aircraft in the holding pattern using altitude separation. As an aircraft exits the holding pattern, the other aircraft in the pattern are successively given clearances to decrease their altitudes to allow other aircraft into the pattern and to maintain the proper separation.

Exiting a holding pattern is always accompanied by a miles in-trail restriction if two or more aircraft are present in the holding pattern and a single exiting altitude exists. Exiting the pattern is generally accompanied by considerable inefficiencies as will be demonstrated later in this paper. The procedures and phraseology for managing exits are simple, however the decisions are complicated. For instance, when should the aircraft be descended, when should normal speed be resumed, when should some other speed be utilized, when should the aircraft be turned early or when should the aircraft be allowed to complete the pattern? The cumulative effect of the difficulties in managing these complexities is to produce a downstream flow of aircraft with widely varying separations. When the downstream facility is requesting and planning for, say, 10 NM in-trail and the traffic arrives with in-trail separations of 10 to 20 NM there are likely to be unused gaps in the traffic that will eventually go to waste. In some cases a decreased throughput at the airport could be attributed to the inefficiencies of the management of holding patterns.

In addition, as holding patterns become full, additional airspace becomes involved. Depending

on the extent of the planning of the holding event, advising an adjoining sector that holding will be required can be disruptive. These additional holds are called “no notice holds”. If the number of these “no notice holds” can be eliminated or reduced, the flow through the center will be smoother with less ad hoc workload on the controllers.

Aircraft using high altitude holding patterns more distant from the airport are more difficult to control. Winds and airspeeds are just two of the factors affecting the extent of the high altitude holding patterns. This may create situations where aircraft encroach upon adjacent airspace, creating the need for “point outs”. Additionally, because of the increased size of the patterns, the difficulty of complying with miles in-trail restrictions on exit is increased.

The following section provides some examples of holding for arrivals to the New York airports.

Examples of Holding Patterns into the New York Airports

As an example of the dynamics of holding patterns, consider the three New York airports – John F. Kennedy International, LaGuardia, and Newark Liberty International. It is very common that there will be holding for these airports in the Washington, Cleveland, Boston and New York Centers.

Track data from the Enhanced Traffic Management System (ETMS) for June 2007 was analyzed by a hold detection algorithm [2] to find the aircraft that were held prior to arriving at these airports. The algorithm determines the position of the hold at the starting time of the hold, the ending time of the hold and the distance traveled in the hold. From ETMS data, the flight identification of the aircraft, the origin and destination airports and the minute-by-minute track reports can be gathered. The position of the aircraft at the start times of the hold during June 2007 for the major New York airports are shown in Figure 1.

3.D.2-2

Figure 1. Holding for New York Airports – June 2007

The holding patterns usually have more than one aircraft holding at a given fix at a given time when there is holding for an airport. As described above, the controllers use altitude separation to manage the holds and to keep the aircraft safely separated. Controllers from the Washington Center have indicated that these holding stacks could contain 6 or 7 aircraft at a time. To observe this in the data we will focus on the arrivals to Newark. The published holding fix locations in the Boston, New York, Cleveland and Washington Centers for the traffic to Newark Airport were identified. The locations of these holding fixes are given in Table 1.

Table 1. Holding Fixes for Newark

Center Fix Name New York PENNS New York FQM New York SHAFF

Boston KODEY Boston HELON

Cleveland SLT Washington ARD Washington STEFE Washington PALEO Washington FAK Washington GVE

The holds shown in Figure 1 were then associated with the fixes in Table 1 by selecting the fix closest to the hold if it is within 20 NM. Once this association was accomplished, the holds for Newark that were considered for the analysis are shown in Figure 2.

3.D.2-3

Figure 2. Newark Hold Associated with Holding Fixes – June 2007

The first thing that was observed is that these fixes had varying amounts holding time as shown in Figure 3. For instance, 16.5% of the time in holding during June 2007 for aircraft bound for Newark took place at PALEO while only 2.6% of the holding time took place at STEFE. The result to note here is that generally the fixes nearest to the center boundary had the greatest percentage of holding minutes. In the Washington Center, ARD and PALEO together had almost one-third of the holding for Newark.

0

500

1,000

1,500

2,000

2,500

PALEO ARD SLT PENNS HELON FAK SHAFF FQM KODEY STEFE

Holding Fixes

Min

utes

of H

oldi

ng

16.5%

10.0%

8.8%

6.1%

4.2%

2.6%

14.6%

13.0% 12.6%

11.6%

Figure 3. Holding Minutes by Newark Holding Fixes

The next thing to observe is how “deep” the holding patterns get. This “depth” determination was done by observing that there were “threads” of holds that were composed of holds that overlapped in time. Once these “threads” were sorted out, a count was made of how many minutes of holding at a fix was accumulated by how many flights

3.D.2-4

simultaneously. It was found that over all the identified holding fixes for Newark during June 2007, nearly 45% of the time there was only a single aircraft in the pattern. (see Figure 4) On the other hand, for more than 55% of the holding time at these fixes there were two or more aircraft in the holding pattern. As pointed out above, having multiple aircraft in a holding pattern significantly increases the controller’s workload.

 

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

1 2 3 4 5 6 7 8 9

Depth of Holding Stack

Min

utes

of H

oldi

ng

44.8%

27.4%

15.1%

7.9%

3.3%1.0% 0.4% 0.1% 0.0%

Figure 4. Holding Stack Depth for Newark Holds

The interesting claim that was made above was that as the holding fixes are farther from the airport, and hence higher in altitude, the accuracy of meeting the miles in-trail restrictions will decrease (i.e., the variation in the miles in-trail separations in the aircraft will increase). To observe this in the data we looked at the times that the aircraft crossed a line nearby, but downstream, from the holding fix. Figure 5 shows the tracks of aircraft associated with the fix ARD. (Newark is in the upper right hand corner of the figure.)

Figure 5. Tracks of Aircraft Held at ARD

r “thre

rse

s of a fix, a variance of ti

It is assumed that every aircraft in a particulaad” will be subject to the same miles in-trail

restriction. If all aircraft in the “thread” traversed the line at equally spaced intervals, then the variance (standard deviation) of the separations (intime) would be zero. If the variance of the separations is greater than zero, this means that inter-aircraft separations are not uniform. The greater the variance, the greater is the non-uniformity of the aircraft separations and the wothe miles in-trail compliance.

For each “thread” of holdme separations of the aircraft crossing the line

associated with that fix was computed. Then, for each fix, the average of these sets of variances was computed. This average then forms a figure of merit for the exit spacing for each fix. If one plots the average variance of the exit separations for eachfix as a function of the distance of that fix from Newark one gets Figure 6. From the figure one can see that there is a correlation between the distance from Newark and the compliance with the miles in-trail restrictions.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 50 100 150 200 250 300

Distance from Newark (NM)

Ave

rage

of T

hrea

d St

anda

rd D

evia

tion

(Min

utes

)

FQM

ARD

HELON

STEFE

PENNS

PALEO

KODEY

SLT

FAK

Figure 7. Average Variance of the Exit

Potential Use of ADS-B to Support

t of Automatic Dependent aft

Separtions for Newark Holding Fixes

Management of Holding Patterns

ADS- Background The basic concep

Surveillance – Broadcast (ADS-B) is that an aircrwill determine its position, usually from the Global Positioning System (GPS), and then broadcast that position, its altitude and speed. This function is

3.D.2-5

commonly referred to as ADS-B Out and has been included in an FAA Notice of Proposed Rule Making (NPRM). If approved, this rule will mandate the equipage of aircraft with the ADSOut function over a defined period.

-B nical

n repo re

he National Airspace System (NA

o it

e in Alas

he S-B

e

of where

r.

the

S-B (both In and Out) proposed. [see e.g., 3] and

)

ld be used to manage holding patterns

1 The techspecifications for this system are provided in numerous RTCA documents [see, e.g., 3, 4, 5].

The FAA plans to take advantage of the ADS-B Out function by listening to these positio

rts and using them as the basis for the futusurveillance system.

The ADS-B features that will be of direct benefit to the users of t

S) will involve the reception of the ADS-Bsignals on board the aircraft. This function is commonly referred to as ADS-B In. There are nplans to mandate this function at this time; andwill evolve as driven by market forces.

Since the year 2000 a demonstration of the ADS-B technology has been taking plac

ka. [6] That demonstration has included several hundred aircraft equipped with both tADS-B Out and ADS-B In functions. The ADOut function was used to place the positions of thaircraft on the controllers’ displays in the Anchorage Center and at Bethel tower as well as to give the aircraft operators a real time viewtheir aircraft are located. The ADS-B In function was used on the aircraft to increase the efficiency of landing operations at Bethel. The demonstration also included the use of the ADS-B In function to receive other data from the ground such as weatheThis information, coupled with a display of terrainin the cockpit, has also positively impacted the safety of flying in Alaska. An extension of that system is now being implemented in the rest of U.S.

There have been many applications for the use of AD

there are ongoing international efforts to collect, evaluate and develop standards for new ADS-B applications [9, 10], generally called Airborne Separation Assistance Systems (ASASfunctions.

We are proposing that in the mature state, ADS-B wou

whe nto

this

e g

roller

Exit with Controller Responsibility

ng pattern eads to poor compliance of the

requ

g ue.

will man t he

ation

sed compute its

traje

LEO

NM 1 The current schedule calls for full equipage by 2020.

reby the controller would clear the aircraft ia holding area and include in the clearance the spacing that should be achieved at the exit of the holding pattern. In this final state, by acceptingclearance the pilot would be taking on the responsibility of maintaining separation from the previous aircraft that he is following into thholding pattern. This is a complex task, envelopinall of the tasks and responsibilities of the contin the current management of holding patterns, so a phased approach to introducing this concept is presented here.

Phase 1 – Hold

As discussed above, exiting the holdiis the event that l

ired in-trail spacing downstream from a hold. The controller needs to judge when to turn the aircraft to exit the holding pattern. With uncertainties in this process, the resulting spacinwill likely be larger than the requested val

In this phase of the use of ADS-B in the management of holding patterns, the controller

age the holds with the same techniques thacurrently uses except when he clears the aircraft for its exit from the holding pattern he adds the phrase “and cleared to follow AAL123 by X NM at 300 kts”. Prior to this clearance the controller decides, perhaps as early as when the aircraft entered the holding pattern, the order in which aircraft will be exiting the pattern. This informis conveyed to the pilot saying “Expect to followAAL123 out of the holding pattern at FL210 and then resume 300 kts”. While the aircraft is in the holding pattern, the pilot identifies the AAL123 using his ADS-B Cockpit Display of Traffic Information (CDTI) instrument.

The avionics is equipped with a CDTI-baASAS function that enables it to

ctory to enable exiting the pattern at a desired interval in miles or minutes. After the pilot identifies AAL123, he selects the AAL123 target, programs in X NM in his CDTI, 300 kts, PA(the fix name) and arms the exit-follow function. When he receives the clearance to follow AAL123out of the holding pattern he activates the exit-follow function. The aircraft’s avionics then calculates the path that will place the aircraft X

3.D.2-6

behind AAL123 at 300 kts. This path may taaircraft around the holding pattern in order to achieve the proper spacing or it may shorten the aircraft’s path in the holding pattern. This pathindicated to the pilot on his CDTI.

ke the

is

than either the

term

ility

g on

th Pilot Responsibility

the e r

e ted after

suita

ing e

– Stack Management with Pilot Responsibility

the entire holding pattern man

ld

2

In this first phase, the spacing on exit from theholding pattern is sufficiently greater

inal or en route separation minima such that the controller can and does retain separation responsibility during the exit operation. In addition the controller retains separation responsibthroughout the hold. The benefit will be the increased uniformity of the inter aircraft spacinthe holding pattern exit.

Phase 2 – Hold Exit wiThis phase will continue to focus on the exit

from the holding pattern. The change will be that xit spacing could be as small as the en route, o

even the terminal area, separation minimum. The actual spacing would be that appropriate for the operation of feeding the terminal area.

The pilot would assume responsibility for thspacing. This phase would be implemen

ble experience with the consistency of Phase 1operations. The controller would still provide the stack management and clear the aircraft out of the holding pattern. The benefit would be that the aircraft would not only be more uniform in their exit spacing but could also provide smaller spacvalues. This would allow the holding pattern to bemptied quicker than the current or Phase 1 holding patterns.

Phase 3

This phase would culminate in the pilots taking responsibility for

agement. In the clearance for the aircraft to enter the holding pattern, the controller wouindicate to the pilot the aircraft he is to follow, theprotocol of the pattern (e.g., as published, or additional instructions if the pattern varies from the

. If

en be eventing aircraft not cleared into the

hold

me-first served basis

es would

ol

ave a holding function. What not have is a hold exit function based on

survs,

tion.

e ways

t issue wou craft

2 The choice of where this guidance is produced in the avionics suite would need to be determined based on how the aircraft would be flown in this maneuver. It may be that coupling to the autopilot may be necessary to conform to airspace requirements.

published information), and the exit clearancethere is no exit clearance (e.g., if there is a hold on traffic over a given fix), the controller would issue an EFC (expect further clearance) in the clearance to enter the holding pattern. The reason for the hold and an estimate of the holding time would also be given, similar to the current holding pattern instructions.

The controller’s responsibility would threduced to pr

ing pattern from entering the holding pattern area. The holding pattern area is part of the designof each published holding pattern.3

If the holding pattern is published, it would be expected to be operated on a first-co

with the efficiencies gained through the more accurate exiting afforded by the ADS-B information. If the holding pattern is ad hoc, in the sense that it is not published, the clearanchave to be more extensive but it would still be operated on a first-come-first-served basis. This is different than the current holding pattern protocthat exists at some high altitude holding patterns in that controllers will extract aircraft at various flightlevels in an attempt to achieve the desired spacing.

Issues Most FMSs h

they do eillance (ADS-B) information. In designing

such automation upgrades to the aircraft’s avionicthere is a tradeoff between level of automation required and the timeframe in which it could be certified and implemented. Any introduction ofadditional data into an FMS (e.g., ADS-B surveillance data) would require a major recertification effort and hence an extendedtimeframe for the introduction of the funcThere may be other less certification intensivof providing a beneficial hold exit function.

Assuming that such a function could be provided in an acceptable timeframe, the nex

ld be of mixed equipage. If not all the airwere capable of hold management, it may not be beneficial to place all aircraft in the same holding pattern. This would require additional solutions

3 Federal Aviation Administration, Order 7130.3A, Holding Pattern Criteria, March 1998.

3.D.2-7

which could include alternative holding patterns founequipped aircraft. This, in turn, would impact airspace and the overall procedure design, particularly in the sectors that commonly use holding to feed large airports.

The self management of holding patterns proposed here envisions a very

r

being procedural process

of al

system

t loss

S

e controller retains the s

there

s f the potential benefits of olding patterns we look to

two

the pattern (a system throughput

2) actor).

multi-holding pattern coordination and the redu

s observed that there was a variation in the differences in the hold exit times.

been noted in [10] and in labo

g fix (referred to as a “thread” in th

and an

t

titude separating aircraft and always transitioning out of the holding pattern at the lowestaltitude. There are holding patterns in thetoday that are “flexible” holding patterns whereby the controller adapts his strategy based on the situational context and a potential operational advantage (e.g., clearing a higher aircraft to exibefore a lower aircraft). It is expected that the of this flexibility will be compensated for by the efficiencies described above but this needs to be shown. It may also be that as experience is gainedwith the proposed Phase III, a more flexible ASAbased design may be possible.

The phases of this concept described above progress from the state where th

eparation responsibility to the state where thepilots accept responsibility for separation. There is a significant issue of pilots accepting responsibilityof separating themselves from more than one other aircraft. This is why the first-come-first-served protocol of the holding pattern has been espoused inthe phased concept. This allows the pilot to separate himself from only the aircraft one flight level below his flight level. That being said, would need to be a safety assessment of this procedure to evaluate the risks and possible mitigations available.

Potential BenefitTo get an estimate o

the self-management of hmeasures

1) the variance of the inter-aircraft spacing on exiting factor), and

communications loading on the controller(a workload f

Other benefits, such as a possible reduction of

ction of closely monitoring the holding pattern, are not addressed here.

Exit Spacing Benefits From Figure 6 it wa

This phenomenon has alsoratory simulations in Europe using ASAS, this

variance was reduced.

This variation can be translated into “lost slots” from the holding fix.4 Assume that each set of aircraft exiting a holdin

e discussion above) is subject to the same miles in-trail restriction. Further assume that the minimum observed inter-aircraft time separation in the thread represents the time necessary to meet the required miles in-trail restriction.5 Therefore, if we sum the inter-aircraft time separations in access of the minimum time separation for a thread we get a measure of the “extra” time between aircraft that results from the inaccuracies of exiting the holding pattern. If this “extra” time is, say, between onetwo times the minimum time separation then we csay that one slot has been lost. If it is between two and three times the minimum time separation then wecan say that two slots have been lost. If one performsthis analysis for all the fixes feeding Newark during June 2007 we find the results shown in Table 2.

Table 2. Slots Lost

Fix Slots Lost Aircraft Slots Lost /Aircraf

ARD 124 248 50.0% STEFE 4 28 14.3% PALEO 230 251 91.6% FAK 69 135 51.1% PENNS 83 296 28.0% FQM 18 89 20.2% SHAFF 0 120 0.0% KODEY 6 36 16.7% HELON 57 234 24.4% SLT 1 02 147 69.4%

4 This is not the same measure as lost slots at the airport

runway because multiple holding fixes can feed a single runway. Also one holding fix can also feed another holding fix which will tend to mitigate the lost slots. However, the number of missed slots at the holding fix is indicative of the efficiency of the operation.

5 This will obviously be a conservative estimate since there is no guarantee that the minimum observed time is really the required miles in-trail restriction. All we know is that the miles in-trail restriction was not broken by this traffic sample.

3.D.2-8

It is most imp ant that th es that the airp re the ones that lose the least

er of slots b e the flow from theswill port.

ave

f to

%

d licable to

the P

flight levels in the holding pattern would

be leient

iciencies.

managing a holding stack issues a command to the ain altitude. The

usua t enter

es

t the t

itable

and he

the stack 20 NM in trail es

y

every

s

ld

or

r’s

ds as today. The benefit will be that the strea

ated

s Beyond this the aircraft would self-

sepa

ment

ssuming the other communications

para for the

ort e fix are closest to ort anumb ecaus e fixes

most directly impact the demand on the airNot counting SHAFF, which did not have many multi-aircraft holds, the three fixes closest to Newark are highlighted in Table 2. One way to interpret this table is that a 50% loss of slots per aircraft (e.g., ARD) could mean that it would htaken half the time to get the aircraft out of the holding pattern and flowing to the airport if the aircraft could have exited the holding pattern uniformly at the required spacing. A 25% loss oslots per aircraft would mean that the time takenempty the holding pattern would have been 25less than if the exit were more uniform.

Since we do not know the actual requested in-trail separations for each of these threads, we coulassume that the above results might be app

hase 1 concept. In Phase 2 the in-trail separation could be smaller and hence the number of missed slots in the June 2007 data would increase.

If the time to empty the holding pattern were less, this would lead one to speculate that thenumber of

ss for the same amount of traffic. Additionally, the frequency of use of less efficholding patterns further from the airports would be less because of the improved pattern effOverall, this would promote a smoother flow of traffic and more consistent pressure on the airport.

Communications Benefits From the discussion above, a controller

pilot to enter the stack at a certl practice is to let each succeeding aircraf

the pattern at a higher altitude than the aircraft that are currently in the pattern. When an aircraft leavthe pattern, it is usually, but not always, the lowest aircraft in the holding stack. This is particularly true of the holding patterns closest to the airport.

As each aircraft is released from the holding pattern, the aircraft at higher altitudes are sequentially given descents. This provides “room a

op” for the next aircraft entering the holding stack and also provides an orderly and equway of managing the stack. In the meantime,

however, the controller has to issue one voice command to the aircraft entering the stack, one voice command to the aircraft exiting the stacka voice command to each aircraft currently in tstack to descend one level.

To get an estimate of the magnitude of the communications load on the controller, let us assume that the aircraft leave

at 350 kts. That means that every 3.4 minutanother aircraft leaves the stack. Further assume that the demand is in equilibrium and that the stackis 6 levels deep. That would mean that every 3.4 minutes the controller would have to issue an entrcommand, an exit command and 5 descent commands. Thus, every 3.4 minutes the controllerissues 7 commands for a communications rate of 123 transmission per hour or a transmission29 seconds just to manage the stack. If each transmission takes the controller perhaps 3 secondto give the command, and perhaps 5 seconds to getan acknowledgement from the pilot, that woumean that the controller would be devoting 27% of his time just to managing this one stack. If this situation were to persist for a while, say an hour more, the controller’s attention would be significantly focused on one area of the controllesector.

In Phases 1 and 2 of the proposed concept the controller would issue the same number of comman

m of aircraft flowing from the holding pattern would be significantly more uniform as estimabove.

In phase 3 the controller would issue only one entry clearance into the stack to follow the previouaircraft.

rate. Assuming a transmission time of, say, 4 seconds rather than 3 seconds, the percentage of time that the controller devotes to the manageof a holding stack that is 6 deep would be 4% for a reduction of 84% over the number of communications that would be used in the current operation.

Figure 8 shows how the reduction of communications load would vary with the depth ofthe stack, a

meters remained constant. Accountingamount of time in holding at each holding fix (see Figure 3) one can determine the reduction in

3.D.2-9

communications time for each fix. This is shown inFigure 9.

 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

1 2 3 4 5 6

Flight Levels in Holding Pattern

Red

uctio

n in

Com

mun

icat

ions

Tim

e

Phases 1 & 2

Phase 3

Figure 8. Reduction in Communications Time as a Function of Number of Flight Levels in

Holding Pattern

 

0%

10%

20%

30%

40%

50%

60%

70%

PALEO ARD SLT PENNS HELON FAK SHAFF FQM KODEY STEFE All Fixes

Holding Fix

Red

uctio

n in

Com

mun

icat

ions

Tim

e

Figure 9. Communications Reduction for Each Holding Fix with the Phase 3 Concept

CThe air traffic at holding fixes for the New

analyzed. What was found was the New York, Washington,

Bost for

ark

was also noted from the data that the inter-aircr

ort

problem was identified, a concept was d

fold.

was

Next Steps wo areas where effort could be

t on

e NAS will be w

onclusions

York airports washolding at fixes in

on and Cleveland centers for aircraft bound the New York airports was significant during June 2007. Focusing on the aircraft destined for NewLiberty International Airport, it was observed that at the fixes designated for that airport more than 50% of time there were more than one aircraft in the holding patterns. Center controllers have indicated that holding aircraft is a high workload activity.

Itaft spacing as aircraft left the holding pattern

was not uniform even though there is a usually a requirement for a certain number of miles in-trail. This situation means that inefficiencies are being introduced in the arrival flow to the airport by holding the aircraft. It was also found that the inefficiencies grew as the distance from the airpincreases. This is primarily due to aircraft being at higher altitudes with greater speeds and greater wind speeds.

After the postulated whereby ADS-B information coul

be used by the aircraft in the holding pattern to self-manage the holding pattern and to exit the holding pattern with more uniform inter-aircraft spacing.

The benefits of being able to do this are two- First, if the aircraft self-manage the holding

pattern, the communications between the controllerand the pilot are significantly reduced. The reduction in communications could be as high as 60%. Second, if the inter-aircraft spacing on exiting the holding patterns were made more uniform by the use of ADS-B information, theholding pattern could have emptied quicker. It estimated that 25% to 50% of the slots were lost per aircraft meaning that the holding patterns could be emptied between 25% and 50% faster. This second benefit also leads to an additional benefit that if holding patterns can be emptied faster there may not need to be additional holding patterns farther from the airport that are being used at the same time.

There are tfocused to move this concept of using ADS-B along. The first area would be to determine if holding patterns in areas of dense traffic areas besides the New York Metropolitan area exhibisimilar behavior and estimated potential benefits a NAS-wide level. The other area would be to develop the detailed requirements for the hold management functions in the avionics.

The contention is that holding in thith us for the foreseeable future. With the

uncertainties in the weather and in the operations at the airports, there will always be a need to keep

3.D.2-10

3.D.2-11

ikely

ng

current Flight Management Systems (FM

to use ADS e

aft

References raffic Control, JO 7110.65S,

th, Aviation System ctive

06,

, Minimum Aviation System ependent

mum Operational Performance

ast ),

Operational Performance )

DO-282A, December 2006.

e Impact of Capstone 5,

for Automatic Dependent O-

st Package of GS/AS

-

ment Definition (OSED). Draft v1.2,

x

ing instructions (ASAS) and

Approved for Public Release; Distribution Number 08-1263. The contents of

r

Arthur P. Smith: apsmith@mitre.org

ateman@mitre.org

2 October 26-30, 2008

pressure on the airports and holding is a natural mechanism for this. With other large airports or airport complexes in the NAS (e.g., Chicago O’Hare, Atlanta, Dallas-Fort Worth) there is lto be holding. An analysis should also cover these locations. In addition, the question about the coordination necessary between multiple holdipatterns servicing the same airport should also be investigated.

Although

Pha

Ss) have a function to fly an aircraft in a holdingpattern, there is no current mechanism in the FMS to use surveillance data (i.e., ADS-B information). This would be a major design change in the FMS with the attendant recertification effort. There maybe other ways to introduce the hold management function into the avionics such as putting the logicthe CDTI (Cockpit Display of Traffic Information). These options should be investigated.

Furthermore, the actual algorithm

Sur

in

A

-B data should be developed. It may be thcase that additional information will need to be transmitted over the ADS-B data link while aircrare in a hold status and these requirements need to be identified.

Jul

[1] FAA, Air TFebruary 14, 2008.

[2] Wright, KennePerformance During the Summer ConveWeather Season, Journal of the TransportationResearch Forum, Volume 45, Number 3, Fall 20pp. 77-92.

[3] RTCAPerformance Standards for Automatic DSurveillance Broadcast (ADS-B), DO-242A, December 2006.

[4] RTCA, MiniStandards for 1090 MHz Extended Squitter Automatic Dependent Surveillance – Broadc(ADS-B) and Traffic Information Services (TIS-BDO-260A, June 2006.

[5] RTCA, Minimum Standards for Universal Access Transceiver (UATAutomatic Dependent Surveillance – Broadcast,

[6] University of Alaska Anchorage, CAASD, Embry Riddle University, Th

se 1 Program (Final Report), September 200www.faa.gov/about/office_org/headquarters_offices/arc/programs/capstone/media/Phase 1 Final with appendices.pdf

[7] RTCA, Development and Implementation Planning Guide

veillance Broadcast (ADS-B) Applications, D249, October 1999

[8] RTCA/EUROCAE, CARE/ASAS Activity 5 Description of a Fir

pplications, CA-02-040(2.2), September 2002, www.eurocontrol.int/care-asas/gallery/content/public/docs/act5/care-asas-a502-040.pdf

[9] RFG (2004). Package I Operational Services and Environ

y 23, 2004. Available selectively at website: extranet.eurocontrol.int/http://vega.eurocontrol.be:8080/login?gw=extranet.eurocontrol.int&domain=etranet.eurocontrol.int

[10] EUROCONTROL, CoSpace: Sequencing arrival flows with spacarrival manager (AMAN): Ground prototyping session (17-19 October 2005), November 8, 2005.

Disclaimer

Unlimited. Casethis material reflect the views of the author and/othe Director of the Center for Advanced Aviation System Development. Neither the Federal Aviation Administration nor the Department of Transportation makes any warranty or guarantee, or promise, expressed or implied, concerning the content or accuracy of the views expressed herein

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7th Digital Avionics Systems Conference

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