April 2003

NASA/TM-2003-212176

Wake Vortex Advisory System (WakeVAS)

Concept of Operations

David Rutishauser, Gary Lohr, David Hamilton, Robert Powers, Burnell McKissick,

Catherine Adams, and Edward Norris

Langley Research Center, Hampton, Virginia

https://ntrs.nasa.gov/search.jsp?R=20030038804 2018-05-15T15:53:08+00:00Z
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April 2003

NASA/TM-2003-212176

Wake Vortex Advisory System (WakeVAS)

Concept of Operations

David Rutishauser, Gary Lohr, David Hamilton, Robert Powers, Burnell McKissick,

Catherine Adams, and Edward Norris

Langley Research Center, Hampton, Virginia
Available from:

NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS)

7121 Standard Drive 5285 Port Royal Road

Hanover, MD 21076-1320 Springfield, VA 22161-2171

(301) 621-0390 (703) 605-6000
1

1.0 Introduction

In response to the growing concern over capacity limitations in the National Airspace System (NAS),

research is active on concepts to alleviate constraints via new operational procedures that may include new

technologies. A concept for mitigating capacity constraints due to the current method of separating aircraft

from wake vortex hazards is described in this report.

1.1 Purpose

NASA LaRC has a rich history of aircraft wake vortex research, with the most recent accomplishment of

demonstrating the Aircraft VOrtex Spacing System (AVOSS) at Dallas/Forth Worth International Airport

in July 2000. The AVOSS was a concept for an integration of technologies applied to providing dynamic

wake-safe reduced spacing for single runway arrivals, as compared to current separation standards applied

during instrument approaches. AVOSS included state-of-the-art weather sensors, wake sensors, and a

wake behavior prediction algorithm. Using real-time data AVOSS averaged a 6% potential throughput

increase over current standards. The AVOSS technologies can be applied to a variety of terminal

operations, including single-runway arrivals and departures, intersecting runway arrivals and departures,

and operations with Closely-Spaced Parallel Runways (CSPRs).

1.2 Current Operations

Current safe wake vortex separations are achieved with a set of rules for air traffic control and procedures

for pilots. The pilot procedures apply any time aircraft are conducting visual approaches and departures.

The procedures summarize safe operational practices based on a general understanding of wake behavior.

These include taking off prior to the liftoff point of a preceding heavier aircraft; landing beyond the

touchdown point of a heavier aircraft; and remaining above the flight path of a heavier aircraft. The rules

are based on the general observation that wakes sink when out of ground effect, and tend to separate

laterally when in ground effect. Ultimately, the responsibility for wake avoidance lies with the pilot during

visual operations.

When instrument approaches are in use, the controller is responsible for applying wake vortex separation

standards. The standards are found in the Air Traffic Controller’s Handbook [1]. These rules depend on

the airport runway configuration and type of operation (arrival or departure). The rules for the airport

terminal area are summarized in Table 1.
2

Table 1 FAA Separation Rules

Type of

Terminal

Operation

Single Runway or

Parallel Runways

Less than 2500’

Apart

Intersecting Runways

Departures Behind B757 or heavy- 120 second hold;

180 seconds if intersection or opposite

direction same runway

OR

Radar separation minima

1. Heavy behind heavy- 4mi

2. Large/Heavy behind B757 –4mi

3. Small behind B757 – 5mi

4. Large behind heavy – 5mi

5. Small behind heavy – 5mi

For pairs not listed the separation is 3 miles

120 seconds behind B757 or

heavy departure or landing if

projected flight paths will cross;

includes parallel runways more

than 2500’ in separation if will

fly through the airborne path of

other aircraft

Arrivals Radar separation minima (at threshold):

1. Heavy behind heavy- 4mi

2. Large/Heavy behind B757 –4mi

3. Small behind B757 – 5mi

4. Large behind heavy – 5mi

5. Small behind large – 4mi

6. Small behind heavy – 6mi

For pairs not listed the separation is 3 miles,

except 2.5 miles in cases when 50 second

runway occupancy time is documented and

other criteria are met

Non-radar minima:

120 seconds for aircraft landing behind an

arriving Heavy/B757, except if follower is

small then 180 seconds

120 seconds for aircraft arriving

after a departing or arriving

B757 or heavy if arrival will fly

through the airborne path of

other aircraft

Also note that for non-radar, timed instrument approaches, the nominal separation is 2 minutes, but it is

increased to 3 minutes for small aircraft behind heavy aircraft due to wake concerns. The controller has the

responsibility of spacing aircraft such that the separations in Table 1 are maintained. The FAA has the

responsibility to ensure that the separations in Table 1 are adequate for wake hazard avoidance. The rules

for wake avoidance were determined empirically with experiments such as tower flybys with wingtip

smoke generators, and represent the worst-case estimation of wake behavior, which is necessary for any

static criteria where safety is of utmost importance. Over the 30+ years of wake vortex research much

progress has been made in quantifying the wake behavior as influenced by atmospheric factors such as

winds, turbulence and thermal stratification. Wake vortex avoidance rules that are sensitive to the

environmental influences on wake behavior could provide more efficient spacing criteria than the worstcase criteria currently used. Research to date indicates substantial capacity improvements can be achieved

by reducing wake constraints. See benefits section for details.
3

1.3 Previous Work

The AVOSS project provided an impetus to advance the state-of-the-art in wake modeling and sensing

technology, as well as weather sensing to support predictions of wake behavior. These technologies were

integrated to address the single runway arrival radar separation rules. Current weather conditions relevant

to wake behavior were sensed and used as a persistence-based forecast to provide inputs to real-time wake

prediction algorithms that were valid for a specified time interval. The predicted wake behavior was

applied to a region of monitored airspace called the safety corridor, which was a rectangular region

centered on the Instrument Landing System (ILS) localizer and glideslope. Wake hazard or residence times

in the corridor were used to compute required spacing for wake avoidance. Wakes could cease to be a

hazard by 1) sinking below the floor of the safety corridor, 2) being advected laterally from the corridor by

crosswinds, or 3) decaying to an intensity below a specified threshold. Real-time wake sensing systems

such as pulsed and continuous-wave (CW) Light Detection and Ranging (LIDAR) systems, and wind-lines

were used to check the results of the prediction system. A prediction of wake vortex behavior is required in

addition to wake sensor observations since spacing recommendations need to have some practical amount

of lead-time and be stable for a certain time interval. For detailed descriptions of the AVOSS see refs [2, 3].

2.0 Concept Description

2.1 Overview

NASA Langley has generalized the system configuration demonstrated in AVOSS to a concept for

minimizing the impact of aircraft wakes on operations by applying the technologies demonstrated in

AVOSS at potentially any airport with any operational configuration. The core enabling components of

AVOSS do not depend directly on the operational application to which they are applied, but the overall

system configuration must be modified for the airport runway configuration and procedures. The AVOSS

technologies produced substantially improved knowledge of wake position and strength as compared to that

implied by current wake separation procedures, and this knowledge can be used to maximize efficiency in

all airport operations. This can be understood further by considering the common requirements for a

system to reduce wake constraints. Figure 1 shows a functional diagram of such a system.

As the flowchart in Figure 1 shows, a region of airspace that will be monitored and assessed for wake

hazard must first be defined. In AVOSS, this region was a rectangular region centered on the ILS localizer

and glideslope for single-runway approaches. In other applications, it could be a wider “fan” for departures,

a cross around the intersection of intersecting runways, or a rectangle around a parallel runway complex.

The dimensions of the region will determine the type of sensors used and their performance specifications.

Once the region is defined, it can be monitored with active wake sensors and prediction algorithms. When

the monitoring shows or predicts a region is free of wake hazard with a certain level of confidence, reduced

spacing procedures can be applied. In the upper branch of Figure 1, a technology-independent solution is

suggested where current wake knowledge implies a permanent, static change to separation criteria in a

limited number of specific operations. An example is the 2500-foot rule, where parallel runways separated

by less than 2500’ must be considered a single runway for wake avoidance procedures. It may be possible

to relax this requirement to a number less than 2500’ for specific airports because of local predominate

meteorological conditions. But the majority of locations and operations are likely to require some kind of

active monitoring and dynamic procedure for an overall significant benefit to the NAS. The lower branch

of Figure 1 shows this type of system, which requires a safety monitor due to the predictive element of

ensuring the protected region is free of wake hazard. The safety monitor would be designed to “catch”

instances of actual conditions diverging from the predicted conditions, and would then apply a default or

fallback procedure.
4

Figure 2 shows a top-level diagram of the technological and configuration options for the Wake Vortex

Advisory System (WakeVAS) CONcept of OPerationS (CONOPS). The left-most box in the block

diagram represents technologies that provide increased knowledge of the wake hazard. In the center are the

procedures, rules, and interfaces that utilize this wake knowledge in a procedure that interfaces to the rest

of the National Airspace System (NAS). The rightmost graphic represents the specifics of the operation

that are addressed by the procedure, or a particular airport’s configuration. Several options exist for the

concept. The concept could be exclusively a ground tool for controllers; it could be a flight deck tool, or a

combination of both. The subsystems could reside totally on the ground, in the air, or a hybrid of the two.

Wake predictions and/or observations could be presented to pilots through a Synthetic Vision System

(SVS) [4] or a Cockpit Display of Traffic Information (CDTI), using on board sensors and computation or

a data-link to a ground based system. This concept, studied in [5], would place the burden of wake

avoidance back on the pilots in all meteorological conditions. This is not a large paradigm shift in terms of

wake avoidance procedures since currently under VMC pilots remain clear of a preceding aircraft’s wake

by adjusting the flight path based on a crude understanding (mental prediction) of wake behavior and

assessment of the current weather conditions. The large paradigm shift lies in whether synthetic vision

systems allow for the introduction of “Electronic Flight Rules” where pilots see and avoid other aircraft and

terrain under IMC using a virtual visual representation of the flight environment.

A time-based inter-arrival spacing tool described in [6] could be used to accurately achieve WakeVAS

spacing recommendations. The spacing tool is a flight deck resource that allows pilots to accept precise

time intervals as a spacing clearance from a leading aircraft. The tool would reduce variances in spacing

produced by current speed-based clearances and improve the benefits realized by the WakeVAS. Wake

limitations could also be displayed as part of the information.

Given the previously described range of technology implementations, NASA Langley Research Center is

focusing on a hybrid system that interfaces to ground controllers, with an optional flight deck data link to

enable wake-vortex hazard information to be communicated to the cockpit. The ground controller uses the

system advisories to implement wake-safe separation of traffic. The wake information sent to the cockpit

would initially be advisory in nature and could serve to increase the flight crew’s Situational Awareness

(SA). Future implementations could allow the pilot to maintain safe wake separation based on information

supplied by a cockpit display.

2.2 Roles and Responsibilities

In the proposed concept, a WakeVAS provides information to a controller for implementing safe wake

spacing through clearances to traffic. The information will be dynamic, with various options for resolution.

In the coarse resolution extreme, the system could provide a wakes-no-factor/wakes-factor with expected

duration advisory. The controller uses this advisory to implement wake-limited or wakes-no-factor spacing,

as prescribed in the current separation standards. The fine resolution implementation will require a

controller approach spacing tool, in which the dynamic (aircraft-to-aircraft) safe spacing minimums are

applied and possibly transparent to the user. Before WakeVAS can provide safe wake-separation

advisories, a formal safety analysis will be required.

The pilot of aircraft equipped to receive and display wake hazard information can use this information for

increased SA during visual approaches and departures, when the responsibility of wake avoidance has been

transferred from the controller to the pilot. If certain regulatory issues such as the acceptance of electronic

flight rules are overcome, the possibility for transferring wake avoidance responsibility to the pilot in IMC

can be introduced. Note that the current concept does not depend on the flight deck display of wake

information, but includes options to facilitate this interface.
5

2.3 Architecture

The WakeVAS architecture is shown conceptually in Figure 2. Starting from the left of the figure, data

fusing algorithms integrate wake measurements, as well as atmospheric inputs from aircraft, terminal and

National Weather Service (NWS) ground sensor systems, and NWS Numerical Weather Prediction (NWP)

models. The atmospheric data provides inputs to the wake behavior prediction algorithms that estimate the

mean and variance of wake positions and strengths. Aircraft information such as type, speed, and weight

are also inputs to the wake prediction algorithms. The observed atmospheric data provides feedback for the

training of probabilistic forecast guidance tools derived from NWP models, which are used to estimate how

the atmospheric conditions that influence wake behavior will vary over time. Wake sensors monitor the

actual wake behavior. The wake and atmospheric observation and prediction subsystems are integrated in a

closed-loop system that constantly compares the predictions to observations. The measurements determine

divergence in predicted and observed wake behavior. The comparison will contribute feedback to the

entire prediction system by 1) providing short term corrections to the predictions, by applying the observed

divergences to increase the variance in the wake parameters used to compute wake hazard durations and 2)

provide the necessary databases for improving probabilistic wake prediction algorithms [7] and training

[8,9] of meteorological model ensembles [10,11] for terminal area NWP. To compute wake hazard

durations, the predicted behavior is applied to a region of protected airspace defined for the particular

airport operation targeted, and safe spacing intervals between aircraft are derived. A safety monitor

function adjusts wake hazard durations appropriately based on the variance in wake and weather

parameters reported by the system.

The spacing data becomes an input to a controller tool or interface, the nature of which depends on the

resolution of spacing adjustments, as discussed previously. The information can also be up linked to

aircraft equipped to use the information in flight deck displays, and Figure 2 shows this link in gray to

illustrate its optional status in the CONOPS.

The WakeVAS concept relies on a number of enabling technologies, some of which were demonstrated

during the AVOSS project. They are listed as follows, with notes on their maturity level:

1. Wake Sensors – The AVOSS utilized pulsed and CW LIDAR [12,13] for measurements of vortex

location and strength. A windline [14] was also used for measurements of vortex lateral position.

Each sensor system used in AVOSS could be classified as a research sensor, but commercial

pulsed LIDARs with wake-measuring capabilities can now be purchased. Detailed performance

specifications of even the commercial LIDAR have yet to be determined. In addition, none of the

AVOSS sensors could measure both wake position and strength in all weather conditions. Due to

this and other limitations research continues on other candidate wake sensors.

2. Weather Sensors – AVOSS used a variety of commercial weather sensors to characterize the wakerelevant terminal area ambient conditions. A down-select of the weather sensors used in AVOSS is

required to determine the minimum necessary WakeVAS sensor suite. Candidates include an

instrumented tower (for low-level wind, temperature, and turbulence measurements), a UHF

profiler with a Radio Acoustic Sounding System (RASS) (low to middle level winds and

temperature), a pulsed LIDAR (serving the dual task of wake and wind measurement), and aircraft

measurements. Aircraft have the potential of measuring all the parameters of interest at a high

resolution, under all weather conditions, over the entire region of interest, and thus represent the

primary means of collecting weather information. Some corroboration with ground sensors is

likely to still be required.

3. Terminal Weather Predictor – A WakeVAS will cause dynamic changes to airport departure and

arrival rates. In order for affected parts of the NAS to react and take advantage of the changes,
6

sufficient advance knowledge of the changes will be required. This can be achieved with an

accurate terminal-area-scale prediction of the relevant environmental parameters that affect wake

behavior. A technology for accomplishing this was demonstrated in the AVOSS project, called the

Terminal Area Planetary Boundary Layer Prediction System (TAPPS) [15]. Emerging

technologies (e.g. ensemble forecasts) are also under consideration for improving terminal-areascale NWP [10,11].

4. Sensor Fusing Algorithms – Data from a variety of sensors with different resolutions/effective

ranges, and operational constraints will have to be integrated into single profiles of winds,

temperature, and turbulence. Algorithms for fusing these sensor inputs (the sensor data often

disagrees, as discovered during AVOSS) must be developed. These algorithms must include

quality control measures so the confidence in the reported parameters can be determined. The

AVOSS included a prototype for this function, see references [2] and [3].

5. Wake Prediction Algorithms – The real-time wake behavior prediction algorithm used in AVOSS

[16] represents the state-of-the-art in a real-time wake model. Despite its sophistication it will not

be adequate for an operational system because it does not specify the wake behavior in a

probabilistic manner. A mean and variance of the wake position and strength is required along

with a confidence measure of those values to perform a formal safety analysis of the system. The

wake prediction algorithm should also be integrated with the weather predictions, observations, and

wake observations in a closed-loop system that adjusts for predictions diverging from observations.

This configuration has not previously been tested.

6. Aircraft Meteorological Data – As mentioned in the discussion on weather sensors, aircraft may be

the only way to get all the required environmental data over the region of interest. Aircraft already

measure and report meteorological parameters, but the resolution of the data is not adequate for a

WakeVAS. The feasibility of obtaining the required resolution data from the aircraft systems has

been demonstrated, but not in real-time.

7. Air/Ground Data Link – The concept requires both meteorological and aircraft state data (e.g.

speed, weight) to be communicated to the ground prediction system. The bandwidth of the link is

still an open research question.

8. Controller Tools/Displays – No controller tool was tested during the AVOSS project. The system

was designed, however to interface through a dynamic set of weight-category dependent spacing

standards to CTAS. A high-resolution spacing tool such as what is included in CTAS is one

option, and at the other spacing resolution extreme is a wake-factor/no-factor with duration

advisory, possibly displayed in a similar manner as the ITWS windshear alerts. The controller tool

is an open design issue.

9. Flight Deck Displays – Similar to the controller tools, no flight deck displays for wake information

have been tested; so many issues such as human factors for the design, symbology, coding, alerting

and display location remain open research questions. A synthetic vision system is one candidate

technology for displaying wake information. Another is a CDTI stand-alone display, or

information integrated with the NAV/Guidance/Multifunction display.

The specifications for some of the technologies above will be driven by the performance requirements

described in the next section.
7

3.0 Operational Environment

3.1 Relevant Environment Parameters

The system performance is determined by the behavior of the aircraft wake vortices in the terminal area,

and how this performance interacts with and is determined by local procedures, traffic loads, traffic mix,

etc. This wake behavior is determined by the type and state (e.g. speed, weight) of the generating aircraft,

and the ambient atmospheric conditions. Relevant meteorological parameters affecting wake behavior in

the terminal area are ambient temperature, wind, and turbulence. Vertical profiles of these meteorological

parameters are necessary in order to predict the wake behavior along the approach and departure paths in

and out of the terminal area. The measurement of these parameters feeds the real-time weather and wake

prediction systems. Archived databases of these parameters allow for determining diurnal, seasonal, and

geographic variability in the terminal area. Mesoscale features, such as frontal zones, outflow boundaries,

and low-level jets will impact WakeVAS functionality since these features often go unpredicted or are

poorly resolved in NWP models as well as model output statistical (MOS) guidance [7]. Although

moisture and air stagnation have negligible affects on wake behavior, they do have an affect on ceiling and

visibility, which, in turn, determines if visual approaches can be used or if instrument approaches are

required. The aircraft parameters vary by location as a function of an airport’s traffic mix. The local

procedures constrain how the wake knowledge can be applied to increase the efficiency of operations. For

example, the runway configuration determines the region of airspace that must be monitored to ensure safe

wake spacing.

3.2 System Performance/Design Parameters

The WakeVAS concept has a number of system design parameters with specifications that depend on the

operation targeted. These parameters and some of their proposed values are summarized for the various

WakeVAS configurations in Table 2.

Table 2

System

Parameter/Type

of Operation

Single

Runway

Arrivals

Single

Runway

Departures

Parallel

Runway

Arrivals

Parallel

Runway

Departures

Intersecting

Runway

Arrivals

Intersecting

Runway

Departures

Weather

Prediction

Interval

30min2hr2min30min30min2hr2min30min30min-2hr 2min-30min

Dimensions of

Protected

Airspace

See

Note 1.

See Note 1. See

Note 1.

See Note 1. See Note 1. See Note 1.

Operational

Weather

Minimums

See

Note 2.

See Note 2. See

Note 2.

See Note 2. See Note 2. See Note 2.

Aircraft Data

Link

See

Note 3.

See Note 3. See

Note 3.

See Note 3. See Note 3. See Note 3.

Error Recovery See

Note 4.

See Note 4. See

Note 4.

See Note 4. See Note 4. See Note 4.

Vortex Hazard

Metric

See

Notes 5,

6

See Notes

5, 6

See

Notes 5,

6

See Notes

5, 6

See Notes

5, 6

See Notes

5, 6
8

Notes

1. The dimensions of the protected airspace depend heavily on the terminal configuration, but in

general it should be a region centered on the mean flight path with an n-sigma buffer added.

AVOSS was centered on the ILS localizer with a 3-sigma buffer for flight technical error added.

Since flight paths are more variable on departures, data must be collected at the installation

location to determine the mean flight paths on which to center the airspace region. Due to this

added complexity on departures a system that only monitors wake decay may be used for this

operation.

2. The weather minimums depend on the requirements the weather and wake sensors must meet. The

dimensions of the protected airspace set maximum and minimum range requirements on both

sensor systems. If the sensor technology used does not function under certain environmental

conditions (i.e. visibility, precipitation) then weather minimums will be relevant.

3. The content of the aircraft to ground data link is known (aircraft type, speed, weight, altitude,

ambient temperature, wind speed, wind direction, and Eddy Dissipation Rate) but the bandwidth of

the link will depend on the required update interval of the predictions, which depends on whether

departures or approaches are targeted. The update interval is also limited by the useful weather

prediction horizon.

4. The proposed wake hazard prediction suite will be designed to catch divergences of system

predictions from actual conditions and correct for them, which should prevent most cases where a

fallback procedure (such as a go-around or ground hold) needs to be applied. These rare-event

procedures still need to be designed for the times the event still occurs. The design of these

procedures is different depending on the targeted operation.

5. Sensor and prediction accuracy concerning the position of the wake vortex depend on a “proximity

hazard metric” that has yet to be defined. The size of the vortex depends on the physical

parameters of the aircraft generating it. The size and trajectory of the following aircraft impacts

how close to the wake core the follower will be influenced by the wake wind field. Assuming that

the probability of a hazardous wake encounter will need to be very low (10-9), the prediction and

sensor systems will need to be specified with a probabilistic output so safety assessments can be

accomplished for system concepts. Note that the wake hazard metric is a common issue that is not

specific to the operation targeted. The type of operation may still determine what aspect of wake

behavior (position or strength) is used to define the hazard.

6. Similar to the wake proximity hazard metric described in Note 5, a threshold for a non-hazardous

wake strength must be determined and agreed upon by all the stakeholders in the NAS. WakeVAS

implementations will not realize their full benefit potential unless wake hazards can be assessed

based on circulation strength. Some WakeVAS implementations such as departures may only be

able to be realized using wake dissipation as a hazard measure. The AVOSS considered a wake to

not be a hazard when its circulation dissipated to a level indistinguishable from background

turbulence. The hazard threshold should be dependent on the encountering aircraft size to realize

full benefit from the system.

3.3 NAS Interface

The interface of a Wake Vortex Avoidance System (WakeVAS) system into the NAS will be accomplished

through the implementation of decision support systems (DSS) and automation tools. These may include

approach spacing tools to provide sequencing, spacing, and runway assignment of aircraft on final

approach to congested airports; including refined considerations for wake vortex and specific aircraft
9

characteristic algorithms. Information display techniques will integrate surface, terminal, and wake vortex

information into a simplified format to support departing and arriving traffic sequencing. The controller,

traffic flow managers, airline operation centers, pilots, and other NAS users will have access to the same

DSS and automation tools, which will enable a collaborative decision making capability. Controller-pilot

data link communications (CPDLC) service supporting air-ground data exchange used in conjunction with

advanced cockpit displays may allow pilots to fly self-separation maneuvers during IFR conditions in the

terminal area [17].

4.0 Scenarios

With the architecture and roles and responsibilities defined, this section describes how the “players” in the

NAS interact with and use the WakeVAS. A “Day in the life” of the WakeVAS is described for the major

terminal operations, describing the sources and flow of information during WakeVAS operation. Key

assumptions and changes from current operations are also summarized. Note that the descriptions in this

section are notional, with specific assumptions intended to serve as examples only, and not to imply final

specifications or requirements.

4.1 Departures

4.1.1 Overview

As stated in Table 1, aircraft departing after a B757 or Heavy category aircraft must be separated with a

time-based hold or distance-based radar separation criteria. This separation cannot be waived by the pilot

or avoided using divergent departure headings. This separation applies to intersecting runways, when the

flight paths of the aircraft operating from each runway could cross.

4.1.2 Significant changes from current operations, procedures, or policies

WakeVAS advisories will allow the separation for aircraft departing behind a B757 or Heavy category

aircraft to be waived or reduced as a function of ambient conditions. Ground Controllers will require

knowledge of the current departure separations being applied as this could impact sequencing; the Local

Controller will also require the information to apply the appropriate minima.

4.1.3 Key Assumptions

The key assumptions for the departure scenarios are as follows:

1. The WakeVAS implementation for the scenarios is not incremental, but a full application of the

technologies described in this CONOPS.

2. The responsibility to separate aircraft remains with the ATSP. No flight deck equipment is

required to implement the concept.

4.1.4 Description of Concept of Operations

The following scenario assumes a single runway, however, the application of the standards would apply to

parallel runway and intersecting runway operations where current procedures require increased separations

based on wake vortex considerations.

Airport X is equipped with a WakeVAS configured to monitor single-runway departures. The system (via

interface) advises the local controller when ambient conditions are such that wakes are no factor for
10

spacing1. The information is conveyed as a separation minimum, and these conditions are predicted to

persist for at least the next hour. The Ground Controller issues taxi instruction in accordance with current

procedures. Sequencing of departures to optimize departure flows (as opposed to “first come, first served”

paradigm) based on pairings may be used. The local controller applies the separation minimum between

departing aircraft. This information is broadcast on the ATIS as an advisory that Reduced Wake Vortex

Separation Standards (RWVSS) are in effect. In one situation, two aircraft are departing for the same fix,

and the departure controller is able to assign divergent courses to transition from the reduced separation

minima to the current radar wake vortex separation minima. Another case involves two eastbound

departures, and due to terrain constraints divergent flight courses cannot be assigned. Here the local

controller must apply the default separation, since the WakeVAS cannot monitor conditions beyond the

immediate terminal area.

4.1.5 Mixed equipage operations

Mixed equipage among the aircraft fleet is not applicable to this CONOPS, since flight deck equipment is

not required. This may change with future implementations. Airport mixed equipage should also not be as

issue, since the WakeVAS will only be used at larger airports that have the necessary infrastructure for a

full implementation.

4.1.6 Non-normal operations

Non-normal conditions are characterized by a condition or configuration of the airplane that would not

normally be experienced during routine flight operations - usually due to failures [18]. This might include:

loss of a required component of a minimum equipment list, electrical failure, display, data link or sensor

failures where information is no longer available to the ATSP, or cannot be transmitted to the ATSP for

dissemination. When a non-normal failure condition occurs, an assessment of the ability of the aircraft to

depart the active runway in a timely manner is determined by communications between pilot and controller.

Spacing strategies will be implemented to accommodate the problem if necessary. Potential scenarios

include delayed takeoff or departing the runway environment as soon as possible. If taxiing, ground traffic

and airport geometries might influence when and where an aircraft can turn off the runway impacting

landing aircraft. If the condition results from a ground event, the controller may determine that spacing

changes are required of one or more inbound and outbound aircraft until the emergency situation condition

is no longer a factor. If the aircraft is disabled and cannot depart the runway, it is assumed that ATSPs will

revert to default spacing and/or procedures.

4.1.7 Rare-normal operations

Rare normal is a fault-free condition that is experienced infrequently by the airplane due to significant

environmental conditions (e.g., significant wind, turbulence, or icing, etc) [18] or non-routine operating

conditions (e.g., out-of-trim due to fuel imbalance, loss of control surface, loss of powerplant, or loss of

critical sensor). If an emergency is declared, the aircraft on the runway is disabled or environmental

conditions warrant a delay in departures, it is assumed that ATSPs will revert to default emergency

handling, spacing and procedures, or implement transition procedures to current default spacing

requirements.

1 For the purposes of this document, the terms “spacing” and “separation” are interchangeable.
11

4.2 Arrivals

4.2.1 Overview

As summarized in Table 1, aircraft arriving during single-runway operations are subject to minimum

separation criteria, which are based on the leader/follower weight categories. For intersecting runways, an

arrival or departure on the intersecting runway delays the arrival on the other runway by 120 seconds if the

preceding aircraft is in the B757 or Heavy category. Parallel runways less than 2500’ apart must be treated

as a single runway for the purposes of spacing the arriving aircraft. In general, arrivals have more

complications than departures in that the aircraft affected must be managed in the air and delay costs are

higher than for aircraft holding on the ground. In addition, aircraft are arriving from a variety of origins so

the valid prediction interval for the WakeVAS needs to be large enough to cover the variance in flight

times.

4.2.2 Significant changes from current operations, procedures, or policies

The primary difference from current operations for arrivals as with departures is that the static separation

rules in Table 1 will serve as an upper limit for dynamic criteria that are output by an advisory system.

Since dynamic spacing will result in changing airport arrival and departure rates, information on these rates

will need to be predicted and communicated through various levels of the NAS. Assuming that the

conditions are such that reduced separation standards can be applied, an AAR that reflects the use of the

reduced standards is provided to the appropriate ATC facilities that affect the flow of traffic into the

airport. In the event of an anticipated transition from the reduced standards to the traditional “static”

standards, the time horizon will dictate the required action to absorb potential delays based from a system

standpoint. The system advisories must be conveyed through displays, realized either as new designs or

modifications to existing displays. For CSPR procedures, the WakeVAS advisories will be used to

determine when paired approaches can be maintained for runways less than 2500’ apart.

4.2.3 Key Assumptions

The key assumptions for the arrival scenarios are as follows:

1. The WakeVAS implementation for the scenarios is not incremental, but a full application of the

technologies described in this CONOPS.

2. As with departures, the responsibility to separate aircraft remains with the ATSP. No flight deck

equipment is required to implement the concept. Technologies that complement the WakeVAS

concept will be considered as optional enhancements.

4.2.4 Description of Concept of Operations

Airport X is equipped with a WakeVAS, configured to monitor single runway arrivals. The WakeVAS

consists of enhancements to the ITWS that was already present, such as a lidar for real-time wake, wind,

and turbulence measurements, data links to aircraft on-board meteorological measurement systems, and

weather and wake prediction algorithms. Environmental data collected as part of the WakeVAS installation

has quantified the expected wake behavior and system benefit to allow the airport officials to set airport

arrival rates, that vary per the season of the year and the time of day. These rates are used by air traffic

management personnel to adjust traffic flow rates and also by the airlines operating at Airport X to

schedule their operations.
12

The WakeVAS continually monitors current conditions and makes predictions for wake-safe spacing

between specific aircraft (or aircraft weight categories) in the terminal area that are guaranteed valid for at

least 30 minutes. Coarser predictions that span multiple hours are used to maintain the validity of the shortterm predictions and anticipate significant AAR changes. Reduced wake vortex separations are provided to

the approach controller on the radar display or on an adjacent monitor. Separation minima could be

provided on the controller’s radar display through inclusion in the aircraft’s data block or by accessing the

data block through “ball tab” (mouse-like device) and keyboard manipulation. A monitor adjacent to the

radar display such as the Systems Atlanta Information Display Systems (SAIDS) [19] could also provide

separation minima in a table or other suitable form. Knowing this data is valid for the time it will take to

land the aircraft, the controller uses it as a guide to issue clearances for minimum wake-safe spacing at the

landing threshold. Traffic Management Coordinators ensure that the flow rates for the subject

airport/terminal area are commensurate with the established AARs through coordination with the

appropriate ATC facilities. Multi-hour predictions that include frontal passage predictions, convective

weather, etc. are used to communicate significant deviated of AAR from prior predictions, and this

information is sent to the appropriate traffic flow management entities (e.g. Air Traffic Control System

Command Center (ATCSCC) and Traffic Management Units (TMUs).

Aircraft inbound to the airport select the Automated Terminal Information Service (ATIS) broadcast that

advertises that RWVSS are in effect when IAPs are in use. (This is beneficial to the flight crew regardless

even though they are receiving control instructions from the ground). In the event that Visual Approaches

are in use, knowledge that although “standards are not being applied, flight crews can expect that wake

vortex is not a consideration in aircraft spacing. One pilot is in a regional jet equipped with a synthetic

vision primary flight display. Upon entering the terminal area, the pilot activates the wake hazard regions

display feature. Using wake behavior data uploaded from the airport WakeVAS, the display shows the

boundaries of the safe flight corridor behind the preceding traffic. The pilot is still accepting a spacing

clearance from the approach controller, since Electronic Flight Rules are still not a reality, but the display

serves to increase the pilot’s situational awareness.

In a differently equipped B-737, the flight crew is advised of the separation that is required behind a

designated lead aircraft by the approach controller (using the WakeVAS information.) Entry of this

distance to onboard systems, such as an approach spacing tool, generates speed cues that the flight crew

follows to achieve the target separation at the threshold. The approach controller continues to monitor and

retain responsibility for separation.

Some afternoon thunderstorms begin forming in the terminal area. Since the climate trends have been

measured this weather was not a surprise, and the average AAR reflects this. Due to the unpredictable

environment in the vicinity of the thunderstorms, the wake vortex spacing applied is no longer reduced

from current standards. The change from the reduced standards was made gradually, since multi-hour

predictions in the WakeVAS anticipated the convective weather.

Airport X also has a large runway that intersects with the primary runway. Since aircraft arriving on the

primary may still be airborne while passing through the airborne flight path of aircraft departing from the

intersecting runway, a 120 second delay was required between the departure and arrival if the departing

aircraft was in the B757 or heavy category. Since a WakeVAS is in operation, the system displays a 50

second wake hazard time for the intersection region, allowing the controller to apply a substantially

reduced time separation to the arriving aircraft.

4.2.5 Mixed equipage operations

Mixed equipage among the aircraft fleet is not applicable to this CONOPS, since flight deck equipment is

not required. This may change with future implementations. Airport mixed equipage should also not be as
13

issue, since the WakeVAS will only be used at larger airports that have the necessary infrastructure for a

full implementation.

4.2.6 Non-normal operations

Non-normal conditions are characterized by a condition or configuration of the airplane or ground

infrastructure that would not normally be experienced during routine operations usually due to failures [18].

This might include: loss of a required component of a minimum equipment list, electrical failure; display,

data link or sensor failures where information is no longer available to the ATSP, or cannot be transmitted

to the ATSP for dissemination. If the condition results from an airborne event, an assessment of the

urgency of landing is performed through communication between pilot and controller. The pilot will

determine if special handling is required and continue based on the ability of the aircraft to maintain

spacing requirements. If the condition results from a ground event, the controller may determine whether or

not spacing changes are required of one or more inbound and/or outbound aircraft until the condition has

been mitigated. If an emergency is declared by the pilot, or a condition on the ground forces a redirection of

traffic flow, it is assumed that ATSPs will revert to default spacing and/or procedures.

4.2.7 Rare-normal operations

Rare normal is a fault-free condition that is experienced infrequently by the airplane due to significant

environmental conditions (e.g., significant wind, turbulence, or icing, etc) [18] or non-routine operating

conditions (e.g., out-of-trim due to fuel imbalance, loss of control surface, loss of powerplant, or loss of

critical sensor). Aircraft will be spaced according to information received or the severity of the condition by

the ATSP, therefore, when a rare normal failure condition occurs, it is assumed that ATSPs will revert to

default emergency handling, spacing and procedures, or implement transition to current default spacing.

5.0 Potential Benefits

5.1 Impacts of System Operation/Safety

Studies have been performed to date [20,21] attempting to quantify the predicted benefit of a WakeVAS

implementation to the NAS. The difficulty in deriving an overall benefit of such a system is twofold: 1)

The complex inter-relationships between the numerous pieces of the system, and 2) The lack of high

resolution meteorological data at the sites of interest.

Since the NAS is a complex system with many dependencies between its elements, changing the

performance of one factor (such as airport arrival rate) has an unknown impact on the system as a whole.

An increased aircraft arrival rate could cause congestion on the taxiways or at the gates, problems with

baggage claim, and increases in ground traffic around an airport. Increases in capacity will likely create

issues with noise abatement, which is a highly sensitive issue at some locations. Comprehensive system

level simulations that take all of the factors into account will be required to quantify overall impacts and

benefits.

A second issue in quantifying WakeVAS benefits is that since the premise of the system operation is to

compute wake-safe spacing that is a function of high-resolution local meteorological conditions, this highresolution data must be collected from all the airports where a WakeVAS will be used. The conditions will

vary by time of day, time of year, and geographic location. Studies such as in [20] only use surface wind

speed and direction as inputs to a WakeVAS decision model. As was observed in the AVOSS field

deployment [30], ignoring a wake behavior factor such as lateral movement or strength in the hazard

computation reduces the projected benefit by as much as 50%. The Dallas departure study in [21] is an
14

example of what can be done for a location where high-resolution meteorological data above ground level

was collected for a significant period of time.

5.2 Capacity Gains

Given the complications described in the previous section, benefits analysis to date suggests changes to the

wake vortex separation standards will have positive impacts on terminal capacity. In [22] the average 6%

potential throughput increase achieved in the Dallas AVOSS demonstration would result in as much as a

40% delay reduction at airports operating near capacity limits, such as Atlanta International Airport. The

Massachusetts Institute of Technology’s Lincoln Labs benefit study using a simulation of departure

operations at Dallas/Ft. Worth projected a yearly savings of five to ten million dollars from reduced delays

resulting from reducing wake separations. The potential savings at many closely spaced parallel runway

airports that must reduce operations from two to one runway under IMC may be even greater. As discussed

in the previous section, not every factor that balances the parameters analyzed in a system as complex as

the NAS has been addressed in these studies, and consequently the potential benefit may be reduced

because of these factors. Therefore, the WakeVAS concept of operations is designed to be adaptable and

able to improve wake-constrained efficiency in a variety of operations.

6.0 Research Issues/Risks

A variety of open research questions remain that prevent completely specifying the CONOPS. They are

listed with explanations in the section.

1. Accuracy/performance of all sensor subsystems – Where possible, each subsystem’s performance

should be understood as well as science permits. The science of measures (metrology) should be

used to understand subsystem uncertainty. This uncertainty may be represented in a probabilistic

manner, such as a confidence probability. This will facilitate system-level trade and safety analysis,

and the generation of detailed subsystem specifications.

2. Development of probabilistic wake predictor – AVOSS is an engineering algorithm that predicts

aircraft wake vortex transport and decay in current and future weather conditions in the terminal

area. Though further research could prove beneficial to the continued development and

improvement of this algorithm, a statistical wake vortex predictor must be considered (See

justification in (1)). Existing wake and meteorological data sets must be expanded to build

databases of relevant wake and meteorological parameters necessary for proper statistical

representation. With proper databases a number of approaches are available. An existing datadriven prediction tool, presently used in NWS operations, is known as Model Output Statistics

(MOS) [7][23]. MOS relates observed weather elements to appropriate predictors via a statistical

approach. MOS guidance enhances NWS operations by 1) objectively interpreting NWP model

output based on a historical sample, 2) predicting events forced by synoptic-scale systems, 3)

correcting for certain systematic NWP model biases, 4) quantifying uncertainty in NWP model

forecasts, and 5) accounting for some local effects by incorporating climatic considerations. To

develop a MOS product for terminal scale prediction, existing wake and meteorological data sets

must be expanded to build the ‘climatologies’ of relevant wake and meteorological parameters

necessary for proper statistical representation. Multivariate analyses, often referred to as multiple

linear regression, would incorporate all existing and future observational data to drive the

development of the statistical wake predictor [24]. The wake characteristics would be predicted

from comparisons of past wake behavior, meteorological model predictions, and real time

meteorological and wake sensors. Another approach is to employ parameter estimation of

algebraic models to provide a probabilistic predictor. Results of a feasibility study to develop a

data-driven statistical vortex predictor using existing wake vortex data are available in [25]. A
15

more robust method would be to use univariate/multivariate time series analysis to provide

predictions without/with prediction error feedback to make an open/closed loop system. One could

also use the point vortex equations and random dynamical theory to develop a set of stochastic

differential equations. Integration of these equations will provide the evolution of a system of

vortices influenced by random effects such as turbulence. In all cases a good database of wake and

meteorological data is necessary for predictor development and validation.

3. Temporal and spatial variation of relevant weather parameters – These research questions have

implications for the weather prediction horizon and the weather sensing requirements. The spatial

(horizontal and vertical) variation of the meteorological parameters monitored will determine the

required coverage and resolution of the ground and airborne weather sensors. The temporal

variation impacts the measurement frequency of the weather sensors and the length of valid

prediction intervals. The atmospheric variability around the terminal will be determined from

meteorological observational field studies. WakeVAS development would get extra benefit from

field studies by providing databases of the relevant meteorological parameters necessary to drive

the development of a statistical wake predictor and training of ensemble meteorological models

(see 6 below).

4. Safety analysis and rare event quantification – Since the proposed system will provide accurate

wake hazard advisories it will need to meet a required level of safety through a formal safety

analysis. All the non-normal and rare-normal events will need to be identified and analyzed as

well.

5. Wake hazard definition – As mentioned in the system parameters section, a wake hazard metric

needs to be defined for the CONOPS, based both on wake proximity and strength, and it should

account for the response and size of encountering aircraft. A good deal of encounter analysis has

been done in both the U.S. and Europe, but a technical and political consensus on what constitutes

a wake hazard has yet to be agreed upon.

6. Quantification of weather prediction horizon – An open research question is the duration in which

a terminal-scale weather prediction is valid, and how the confidence in the predictions evolves with

time. The WakeVAS will have different NAS-level impacts depending on the amount of lead-time

that exists prior to system changes. New model techniques are currently being researched and

implemented operationally to predict weather at the highest possible fidelity. A modeling

technique under consideration for potential employment into the WakVAS system is known as

ensemble modeling [8,9,10,11]. Ensemble forecasting is using a collection of individual forecasts

valid at the same time to determine parameter mean and standard deviation. Observations are used

to ‘train’ the ensemble to reduce the standard deviations, and therefore, improve forecast skill in

space and time. As observations are obtained, the ensembles are reinitialized with updated

weighting functions that improve the forecasts at longer time periods.

7. Controller/Pilot workloads/Display design – Many open research issues remain primarily in the

human factors area regarding display design and the human interface for the WakeVAS.

WakeVAS impacts on a controller’s workload are not currently known, nor the impact wake

information in the cockpit has on a pilot’s situational awareness. Future ATSP display

representations integrated into scope symbology should be analyzed to assess appropriate coding of

information, interpretive quality, display effects and cognitive workload. If controller display is

such that the system advisories are transparent, (e.g. aFAST, pFAST) these issues should be

minimized.

8. Data link requirements – The aircraft-to-ground data link requirements to support the WakeVAS

CONOPS need to be quantified. More information will need to be communicated at a higher
16

frequency than is currently done for aircraft weather data, and links such as ADS-B do not have all

the necessary WakeVAS parameters to date.

9. Lack of high resolution weather data – One major obstacle in performing cost/benefit studies for a

WakeVAS concept is the current lack of the high resolution terminal area weather data needed to

project ranges of wake behavior and the associated effectiveness of an active wake spacing system.

Furthermore, performance of statistical wake and meteorological prediction models is dependent

on the quantity and quality of observed data. Research in obtaining this data from an effective

combination of aircraft, field measurements, and weather models is currently active.

10. NAS impacts – As mentioned in (6), a WakeVAS will have system-level affects in the NAS,

primarily by modulating airport acceptance rates. The impact of such a system is not currently

known and will have to be studied via simulation.

7.0 Transition Issues

The WakeVAS concept is consistent with the FAA’s Operational Evolution Plan (OEP) for the NAS [26].

Under the objective “Keep Terminal Throughput Closer to Visual Levels in all Weather Conditions” there

are two solutions that depend on wake vortex spacing limitations. These are “Maintain Runway Use in

Reduced Visibility”, and “Space Closer to Visual Standards”. Changing the wake vortex separation rules

concerning parallel arrivals and departures in Table 1 enables allowing parallel runways to remain

independent under reduced weather minimums. Similarly, reduced separation on approach and departure

for all runway configurations requires reduced wake spacing rules to support spacing closer to visual

operations. WakeVAS concepts are also consistent with the RTCA 2000 NAS Concept of Operations [27].

In Chapter 5, “Arrivals and Departures”, the RTCA document describes automatic exchanges of

information between service providers and aircraft to include weather and hazard alerts such as wind shear,

microburst, and wake vortex. Specifically, the RTCA document calls for increased pilot situational

awareness through the use of CDTI, to be expanded to include wake vortex separation with other traffic.

Increased use of FMS approaches is also considered, and real-time weather data links mentioned in the

document will enable these approaches to use weather-dependent wake vortex separation criteria. Finally,

the RTCA recommends using enhancements in real-time wake turbulence detection and prediction to

enable rates achieved for Visual Approaches when Instrument Approaches are in use. These may be

realized in part by information provided to the service provider to enable dynamic wake separation rules.

The RTCA’s NAS Concept of Operations document is divided into short (through 2005), mid (2005-2010)

and long (2010-2015) term concepts. The RTCA timeframes are consistent with WakeVAS

implementation plans, described in a draft FAA/NASA Wake Vortex Research Management Plan (RMP)

[28]. The RMP defines short, mid, and long-term milestones that prescribe a phased implementation of

wake vortex procedures and technology into the NAS. Short-term milestones focus on data collection to

support static procedural changes, where enough understanding of wake behavior can be accumulated to

justify a procedure based on knowledge that the wake “never behaves a certain way”. Since wake behavior

is dependent on the characteristics of the generating aircraft and the ambient weather conditions, static

procedure changes may only be possible in a small number of airports with relatively stable geographic and

weather characteristics and other enabling constraints such as a parallel runway configuration. The shortterm efforts will create precedents in changing wake separation rules that will facilitate the mid and long

term milestones.

Mid-term solutions include procedures that have a dynamic aspect in that they are dependent on some

ambient weather condition. The condition could be a climatological categorization of winds, as was done

for the Wake Vortex Warning System (WVWS) in Frankfurt, Germany [29]. Another potential system
17

concept is discussed in [30], where turbulence measure of the atmosphere is used to predict when wakes

will dissipate at a rate high enough to not be a spacing factor. Mid-term milestones will enable the first

dynamic wake separation procedures, and advance weather sensing capabilities at airports necessary to

support the procedures.

The RMP classifies long-term procedures as those that use active, real-time, wake vortex sensing and

prediction. This covers the current WakeVAS concept. WakeVAS is considered long-term because it

requires the introduction of the most technology that will have to mature to a level at which it can be

certified. This concept has the most unanswered research questions. Data collected during the mid and

short term efforts can serve the dual purpose of supporting the current effort and providing data for longterm technology development.

Development of high-fidelity technology models for concept simulations will mitigate risk by enabling

concept safety analysis and cost/benefit analysis. Field data collection efforts and prototype deployments

will be guided by the simulation studies, so operations and locations with the highest potential benefit can

be targeted. Several political/policy changes will need to occur to support the CONOPS. Examples are an

augmentation to the current wake separation rules to allow for dynamic, system-provided separations, and

consensus on a wake hazard metric. More changes will be required, such as the introduction of “Electronic

Flight Rules” before wake separation responsibility can be transferred to the pilot. Several NAS

infrastructure changes will also be required, such as augmentations to terminal weather suites and aircraft

data link message requirements.

8.0 Summary

Current safe wake vortex separations are achieved with a set of rules for air traffic control and procedures

for pilots. The rules and procedures are based on the general observation that wakes sink when out of

ground effect, and tend to separate laterally when in ground effect. The previous 30 years of wake vortex

research have enabled the development of technologies that have been shown feasible to produce a realtime knowledge of wake behavior. The AVOSS project demonstrated the technical capability of real-time

wake sensing systems such as pulsed and CW LIDARs, weather and wake prediction systems, and the

potential of integrating these subsystems with a procedure that could increase an airport’s capacity. The

next step is to take this concept of environmentally reduced wake separation from the technically possible

to practical application. The current concept proposes a system to provide wake safe minimum spacing,

which is communicated to controllers and used to space aircraft efficiently during instrument operations.

The potential for linking the wake hazard information to the cockpit to improve pilot’s situational

awareness during visual operations is also recognized. To do this, a plan detailing the required

communications, navigation, and surveillance infrastructure as well as defining the operational procedures

needs to be developed and implemented. WakeVAS has the potential to dramatically increase the capacity

while maintaining at least the current level of safety at many airports, by using the technology available

today and in the near future. This report includes open research issues that need to be addressed to achieve

an implementation of the concept, and transition issues that affect how this implementation would occur.
18

9.0 Figures

Figure 1 WakeVAS functional block diagram
19

Figure 2 WakeVAS Architecture

Aircraft Meteorological

& State Data

Airport Wake and Weather Sensor Suite

• Sensor Data Fusing Algorithm

• Wake Prediction Algorithm

• Terminal Weather Predictor

NWS Data

• Wake Hazard

Computations

• Safety Monitor

Flight Deck

Display/

Nav/Guidance

Interface

Controller Tool

Aircraft/Ground Data Link

Aircraft/Ground Data Link

Protected

Airspace

Definition

Aircraft Meteorological

& State Data

Airport Wake and Weather Sensor Suite

• Sensor Data Fusing Algorithm

• Wake Prediction Algorithm

• Terminal Weather Predictor

NWS Data

• Wake Hazard

Computations

• Safety Monitor

Flight Deck

Display/

Nav/Guidance

Interface

Controller Tool

Aircraft/Ground Data Link

Aircraft/Ground Data Link

Protected

Airspace

Definition
20

10.0 List of Acronyms

AAR Airport Arrival Rate

ADS-B Automatic Dependent Surveillance Broadcast

ATC Air Traffic Control

ATCSCC Air Traffic Control System Command Center

ATIS Automated Terminal Information Service

ATSP Air Traffic Service Provider

AVOSS Aircraft Vortex Spacing System

CDTI Cockpit Display of Terminal Information

CONOPS Concept of Operations

CPDLC Controller Pilot Data Link Communications

CSPR Closely Spaced Parallel Runways

CTAS Center TRACON Automation System

CW Continuous Wave

DSS Decision Support System

FAST Final Approach Spacing Tool

FAA Federal Aviation Administration

FMS Flight Management System

IAP Instrument Approach Procedure

IFR Instrument Flight Rules

ILS Instrument Landing System

IMC Instrument Meteorological Conditions

ITWS Integrated Terminal Weather System

LIDAR Laser Detection and Ranging

MOS Model Output Statistics

NAS National Airspace System

NAV Navigation

NWS National Weather Service

NWP Numerical Weather Prediction

OEP Operational Evolution Plan

RASS Radio Acoustic Sounding System

RTCA Radio Technical Commission for Aeronautics

RMP Research Management Plan

RWVSS Reduced Wake Vortex Separation Standards

SA Situational Awareness

SAIDS Systems Atlanta Information Display System

SVS Synthetic Vision System

TAPPS Terminal Area (Planetary Boundary Layer) Prediction System

TRACON Terminal Radar Approach Control

TMU Traffic Management Units

UHF Ultra High Frequency

VMC Visual Meteorological Conditions

WakeVAS Wake Vortex Advisory System

WVWS Wake Vortex Warning System
21

11.0 References

1 Air Traffic Controller’s Handbook, FAA Order# 7110.65N.

2 Hinton, D.; Description of Selected Algorithms and Implementation Details of a Concept-Demonstration Aircraft

VOrtex Spacing System (AVOSS), NASA/TM-2001-211027, June 2001.

3 Hinton, D., Charnock, J., Bagwell, D.; Design of an Aircraft Vortex Spacing System for Airport Capacity

Improvement, AIAA 2000-0622, 38th AIAA Aerospace Sciences Meeting & Exhibit, January 2000, Reno, NV.

4 Williams, D., Waller, M., Koelling, J.; Concept of Operations for Commercial and Business Aircraft Synthetic

Vision Systems Version 1, NASA/TM-2001-211058, December 2001.

5 Holforty, W., Powell, D.; Flight Deck Display of Airborne Traffic Wake Vortices, 20th DASC Conference Daytona

Beach, FL, 14-18 October 2001.

6 Oseguera-Lohr, R., Lohr, G., Abbott, T.; Evaluation of Operational Procedures for Using a Time-Based Airborne

Inter-Arrival Spacing Tool, AIAA Aircraft Technology, Integration, and Operations Conference AIAA-2002-5824,

October 2002.

7 Glahn, H.R., and Lowry, D.A.: The Use of Model Output Statistics (MOS) in Objective Weather Forecasting,

Journal of Applied Meteorology, Vol. 11, December 1972, p. 1203-1211.

8 Krishnamurti, T.N., Kishtawal, C.M, Zhang, Z., LaRow, T., Bachiochi, D. Williford, E., Gadgil, S., Surendran, S.:

Multimodel Ensemble Forecasts for Weather and Seasonal Climate, Journal of Climate, Vol. 13, December 2000, pp.

4196-4216.

9 Krishnamurti, T.N., Kishtawal, C.M, Shin, D.W., D. Williford: Improving Tropical Precipitation Forecasts from a

Multianalysis Superensemble, Journal of Climate, Vol. 13, December 2000, pp. 4217-4227.

10 Stensrud, D.J., Brooks, H.E., Du, J., Tracton, S., and Rogers, E.: Using Ensembles for Short-Range Forecasting,

Monthly Weather Review, Vol. 127, April 1999, pp. 433-446.

11 Hamill, T.M., and Colucci, S.J.: Verification of Eta-RSM Short-Range Ensemble Forecasts, Monthly Weather

Review, Vol. 125, June 1997, pp. 1312-1327.

12 Campbell, S., Dasey, T., Freehart, R., Heinrichs, R., Matthews, M., Perras, G., Rowe. G.; Wake Vortex Field

Measurement Program at Memphis, TN Data Guide, MIT Lincoln Laboratory Project Report NASA/L-2, 14 January

1997.

13 Britt, C.; Estimation of Aircraft Wake Vortex Characteristics from Coherent Pulsed Lidar Measurements, Research

Triangle Institute Report RTI/4903/032-01F, January 1997.

14 Rudis, R., Burnham, D., Jacobs, L.; AVOSS Windline at Dallas/Ft. Worth Airport, Volume 1, Installation and

Operation, DOT-VNTSC-RSPA-01-01, March 2001.

15 Kaplan, Michael L.; Lin, Yuh-Lang; Charney, Joseph J.; Pfeiffer, Karl D.; Ensley, Darrell B.; DeCroix, David S.;

and Weglarz, Ronald P.: A Terminal Area PBL Prediction System at Dallas-Fort Worth and its Application in

Simulating Diurnal PBL Jets, Bulletin of the American Meteorological Society, Vol. 81, No. 9, September 2000.

16 Robins, R., Delisi, D.; NWRA AVOSS Wake Vortex Prediction Algorithm Version 3.1.1, NASA/CR-2002-211746,

June 2002.

17 National Airspace System Architecture, Version 4.0, Federal Aviation Administration, January 1999.

18 RTCA DO178

19 http://www.sysatl.com

20 Hemm, R., Shapiro, G., Lee, D. et al. Benefit Estimates of Terminal Area Productivity Program Technologies,

NASA/CR-1999-208989, January 1999.

21 Shaw, J., Cole, R.; Potential Benefits of Reducing Wake-Related Aircraft Spacing at the Dallas/Fort Worth

International Airport, MIT Lincoln Laboratory Project Report ATC-304, 12 July 2002.

22 O’Connor, C., Rutishauser, D.; Enhanced Airport Capacity Through Safe, Dynamic Reductions in Aircraft

Separation: NASA’s Aircraft VOrtex Spacing System (AVOSS), Journal of Air Traffic Control, Volume 43, No. 3,

October-December 2001, p. 4-10.

23 http://www.nws.noaa.gov/mdl/synop/mos2.htm

24 D'Odorico, P., Over, T.M., and Yoo, J-C.: Stochastic multivariate analysis of hydrometeorological variables for

wind erosion models, Proceeding of ICAR5/GCTE-SEN Joint Conf., International Center for Arid and Semiarid

Lands Studies, Texas Tech Univ., Lubbock, TX, July 2002, 5 pp.

25 Lai, D.Y. and Delisi, D.P.: Feasibility Study for the Development of a Data-Driven Vortex Model, Northwest

Research Associates Inc., NWRA-CR-03-R252, March 2003.

26 http://www.faa.gov/programs/oep/

27 http://www.rtca.org/
22

28 FAA/NASA Wake Turbulence Research Management Plan Version 1.1, working draft, October 2002 (unpublished).

29 Gurke, T., Lafferton, H.; The development of the wake vortex warning system for Frankfurt airport: Theory and

implementation, Air Traffic Control Quarterly, Vol. 5, No. 1, pp. 3-29.

30 Donohue, G., Rutishauser, D.; The Effect of Aircraft Wake Vortex Separation on Air Transportation Capacity,

Presented at 4th USA/Europe Air Traffic Management R&D Seminar, December 3-7, 2001, Santa Fe, New Mexico.

Paper No. 22.
REPORT DOCUMENTATION PAGE Form Approved

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other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations

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0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

April 2003

3. REPORT TYPE AND DATES COVERED

Technical Memorandum

4. TITLE AND SUBTITLE

Wake Vortex Advisory System (WakeVAS) Concept of Operations

5. FUNDING NUMBERS

727-04-10-01

6. AUTHOR(S)

David Rutishauser, Gary Lohr, David Hamilton, Robert Powers, Burnell

McKissick, Catherine Adams, and Edward Norris

 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

8. PERFORMING ORGANIZATION

REPORT NUMBER

 L-18281

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA/TM-2003-212176

11. SUPPLEMENTARY NOTES

 

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited

Subject Category 03 Distribution: Nonstandard

Availability: NASA CASI (301) 621-0390

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

NASA Langley Research Center has a long history of aircraft wake vortex research, with the most recent

accomplishment of demonstrating the Aircraft VOrtex Spacing System (AVOSS) at Dallas/Forth Worth

International Airport in July 2000. The AVOSS was a concept for an integration of technologies applied to

providing dynamic wake-safe reduced spacing for single runway arrivals, as compared to current separation

standards applied during instrument approaches. AVOSS included state-of-the-art weather sensors, wake

sensors, and a wake behavior prediction algorithm. Using real-time data AVOSS averaged a 6% potential

throughput increase over current standards. This report describes a Concept of Operations for applying the

technologies demonstrated in the AVOSS to a variety of terminal operations to mitigate wake vortex capacity

constraints. A discussion of the technological issues and open research questions that must be addressed to

design a Wake Vortex Advisory System (WakeVAS) is included.

14. SUBJECT TERMS

Aircraft wake vortices; Aircraft spacing; AVOSS; Air traffic control

15. NUMBER OF PAGES

27

 16. PRICE CODE

 

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION

 OF ABSTRACT

Unclassified

20. LIMITATION

 OF ABSTRACT

 UL

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z-39-18

298-102