All About Aviation

Traffic Information

Definition

Traffic information is information issued by an air traffic services unit to alert a pilot of other known or observed air traffic which may be in proximity to the position or intended route of flight and to help the pilot avoid a collision. (ICAO Doc 4444: PANS-ATM.)

Traffic Information in ATC Provision

Controllers may provide traffic information to pilots or to request pilots to pass the information to the other crews. Pilots may also request traffic information. In controlled airspace some flights may not be provided with air traffic clearances but they must receive traffic information from ATC. For example, in class “C” airspace VFR flights receive traffic information in respect of other IFR and VFR flights. (Further information about the type of air traffic services provided in the different classes of airspace is available in the Classification of Airspace article.)

According to ICAO Doc 4444 provisions the traffic information message shall comply with the following phraseology:

To pass traffic information

a) (ATC) TRAFFIC (information);

b) (ATC) NO REPORTED TRAFFIC;

To acknowledge traffic information

c) (Pilot) LOOKING OUT;

d) (Pilot) TRAFFIC IN SIGHT;

e) (Pilot) NEGATIVE CONTACT (reasons);

f) (ATC) (ADDITIONAL) TRAFFIC (direction) BOUND (type of aircraft) (level) ESTIMATED (or OVER) (significant point) AT (time);

g) (ATC) TRAFFIC IS (classification) UNMANNED FREE BALLOON(S) WAS [or ESTIMATED] OVER (place) AT (time) REPORTED (level(s)) (or LEVEL UNKNOWN) MOVING (direction) (other pertinent information, if any).

Traffic information can be also included in the ATC clearances concerning take off, landing and multiple line-ups. Where reduced runway separation minima between aircraft for the same runway is used, the provision of traffic information to the flight crew of concerned succeeding aircraft is a condition for application of the reduced runway separation minima.

Traffic Information and Avoiding Action Phraseology

According to Doc 4444 controllers shall provide traffic information to pilots when issuing avoiding action instructions in the following manner:

Traffic Information (ATC) TRAFFIC (number) O’CLOCK (distance) (direction of flight) (any other pertinent information):

UNKNOWN;
SLOW MOVING;
FAST MOVING;
CLOSING;
OPPOSITE (or SAME) DIRECTION;
OVERTAKING;
CROSSING LEFT TO RIGHT (or RIGHT TO LEFT);
(aircraft type - if known);
(level);
CLIMBING (or DESCENDING);

Avoiding Action
(ATC) DO YOU WANT VECTORS?;
(Pilot) REQUEST VECTORS;
(ATC) TURN LEFT (or RIGHT) (number of degrees) DEGREES IMMEDIATELY TO AVOID (UNIDENTIFIED) TRAFFIC AT (bearing by clock-reference and distance).
(ATC) CLEAR OF TRAFFIC (appropriate instructions);

Traffic Information Related to Emergency Separation and Descent

Emergency Separation

When emergency separation is applied the flight crews concerned shall be advised that emergency separation is being applied and shall be informed of the actual minimum used. Additionally, all flight crews concerned shall be provided with essential traffic information.

Emergency Descent

Controller can provide traffic information to pilots concerned by the emergency descent aircraft as given bellow:

a) (Pilot) EMERGENCY DESCENT (intentions);

b) (ATC) ATTENTION ALL AIRCRAFT IN THE VICINITY OF (or AT) (significant point or location) EMERGENCY DESCENT IN PROGRESS FROM (level) (followed as necessary by

specific instructions, clearances, traffic information, etc.).

(Further information is provided in article Emergency Descent: Guidance for Controllers)

Traffic Information To Aircraft Operating Outside Controlled Airspace

Due to the variety of factors influencing the nature of the flight information services and particularly the provision of information on possible collision hazards to aircraft operating outside controlled airspace, it is not possible to specify standard texts for these types of messages.

In provision of AFIS, EUROCONTROL Manual of Aerodrome Flight Information Services specifies that the following information shall be provided as appropriate:

a) direction of flight of aircraft concerned

b) type and wake turbulence category (if known) of aircraft concerned;

c) level of aircraft concerned, including eventual changes;

d) relative bearing of the aircraft concerned in terms of the 12-hour clock as well as distance from the conflicting traffic; or

1) actual or estimated position of the aircraft concerned; or

2) estimated times; and

e) any other information considered relevant (e.g. approaching, crossing the traffic information area/traffic information zone (TIA/TIZ), estimated take-off or landing time).

Essential Traffic Information

Essential traffic is controlled traffic to which the provisions of separation by ATC are applicable, but which, in relation to a particular controlled flight, is not, or will not be, separated from other controlled traffic by the appropriate separation minimum (Doc 4444, par. 5.10.1.1). According to ICAO requirements, essential traffic information shall be given to controlled flights concerned whenever they constitute essential traffic to each other.

Essential traffic information will inevitably relate to controlled flights cleared subject to maintaining own separation and remaining in visual meteorological conditions and also whenever the intended separation minimum has been infringed.

Content of Essential Traffic Information

Essential traffic information shall include:

a) direction of flight of aircraft concerned;

b) type and wake turbulence category (if relevant) of aircraft concerned;

c) cruising level of aircraft concerned; and

1) estimated time over the reporting point nearest to where the level will be crossed; or

2) relative bearing of the aircraft concerned in terms of the 12-hour clock as well as distance from the conflicting traffic; or

3) actual or estimated position of the aircraft concerned.

Wake turbulence category is considered to be essential traffic information if the aircraft concerned is of a heavier wake turbulence category than the aircraft to which the traffic information is directed.

Essential Local Traffic Information

Information on essential local traffic shall be issued in a timely manner, either directly or through the unit providing approach control service when, in the judgement of the aerodrome controller, such information is necessary from a safety point of view, or when requested by aircraft.

Essential local traffic is considered to consist of any aircraft, vehicle or personnel on or near the manoeuvring area, or traffic operating in the vicinity of the aerodrome, which may constitute a hazard to the aircraft concerned. Essential local traffic must be described so as to be easily identified.

Content of Essential Local Traffic Information

According to Doc 4444 provisions (par. 11.4.3.1.3) the essential local traffic information must include:

a) identification of the aircraft to which the information is transmitted;

b) the words TRAFFIC IS or ADDITIONAL TRAFFIC IS, if necessary;

c) description of the essential local traffic in terms that will facilitate recognition of it by the pilot, e.g. type, speed category and/or colour of aircraft, type of vehicle, number of persons;

d) position of the essential local traffic relative to the aircraft concerned, and direction of movement.

ACAS: Guidance for Controllers

Description

This article provides guidance for controllers on what to expect from aircraft experiencing the effects of ACAS RA, together with some considerations which will enable the controller to provide as much support as possible to the aircraft concerned, as well as maintaining the safety of other aircraft in the vicinity of the potential collision.

There is no set of ready out-of-the-box rules to be followed universally. As with any unusual or emergency situation, controllers should exercise their best judgment when dealing with the apparent consequences of loss of separation (LOS) between aircraft, including those indicated by ACAS resolution advisories (RAs). A generic checklist for handling unusual situations is readily available fromEUROCONTROL but it is not intended to be exhaustive and is best used in conjunction with local ATC procedures.

Useful to Know

The Airborne Collision Avoidance System (ACAS) is an airborne safety net and an ICAO standard which provides pilots with a system independent of air traffic control to detect the presence of other aircraft which may present a threat of collision. Where the risk of collision is established, the system provides an indication of a vertical manoeuvre that will reduce the risk of collision. It is often used by the flight crew to improve their situational awareness. (See also: Incorrect Use of TCAS Traffic Display). It serves as a last-resort safety net irrespective of any separation standards.

ICAO Standards and Recommended Practices (SARPs) and procedures on ACAS are contained in: Annex 10, volume IV; PANS-OPS (Doc. 8168) and PANS-ATM (Doc. 4444). The Regional and Supplementary Procedures document (ICAO Doc. 7030) and ICAO Annex 6 specify the ACAS II equipage requirements. Additionally, many aviation authorities (including EASA in Europe, FAA in USA, CASA in Australia, etc.), have mandated by a regulation the equipage of TCAS II compliant with ICAO SARPS in a variety of aircraft classes.

According to ICAO (Doc 8168 PAN-OPS, Chapter 3, Section 3.2) in case of a conflict between TCAS RA and air traffic control (ATC) instructions, the ACAS RA always takes precedence (this is mainly because the ACAS uses more accurate information which provides more current and comprehensive picture of the situation.

On July 1, 2002 over Überlingen, Germany a mid-air collision resulted when the crews of the two airplanes fitted with TCAS II systems were following two different operational concepts, due to lack of standardisation. The crew of one of the airplanes followed the ACAS RA, the other, followed the controllers’s instructions which were in contradiction with the ACAS generated RA. See: T154 and B752, Überlingen Germany, 2002 (LOS HF).

Effects

An ACAS RA might result in:

Climb or descent without prior warning
Changes in vertical rates of climb/descent
Two or more aircraft involved
Only one aircraft in a conflict pair getting an ACAS RA
Late notification by pilots regarding RA, after aircraft begin climb or descent (in accordance with the principle aviate, navigate, communicate)

Anticipated Crew Actions (Impact on Crew)

In the event of an RA the crew is expected to act in accordance with PANS-OPS (Procedures for Air Navigation Services - Aircraft Operations - Volume I Flight Procedures - ICAO Doc. 8168 OPS/611):

Respond immediately by following the RA as indicated, unless doing so would jeopardise the safety of the airplane;
Follow the RA even if there is a conflict between the RA and ATC instruction to manoeuvre;
Do not manoeuvre in the opposite sense to an RA (In the case of an ACAS-ACAS coordinated encounter, the RAs complement each other in order to reduce the potential for collision. Manoeuvres, or lack of manoeuvres, that result in vertical rates opposite to the sense of an RA could result in a collision with the threat aircraft.);
As soon as possible, as permitted by flight crew workload, notify the appropriate ATC unit of any RA which requires a deviation from the current ATC instruction or clearance. (Unless informed by the pilot, ATC does not know when ACAS issues RAs. It is possible for ATC to issue instructions that are unknowingly contrary to ACAS RA indications. Therefore, it is important that ATC be notified when an ATC instruction or clearance is not being followed because it conflicts with an RA.);
Promptly comply with any modified RAs;
Limit the alterations of the flight path to the minimum extent necessary to comply with the RAs;
Promptly return to the terms of the ATC instruction or clearance when the conflict is resolved;
Notify ATC when returning to the current clearance.

The following additional notes are important and should be taken into consideration when anticipating the crew’s actions in response to ACAS RA:

Stall warning, wind shear, and ground proximity warning system alerts have precedence over ACAS RA.
High vertical rate (HVR) encounters - Pilots are advised to use appropriate procedures when climbing or descending to an assigned altitude or flight level, especially with an autopilot engaged. HVR could occur at a rate around 1 500 ft/min throughout the last 300 m (or 1 000 ft) of climb or descent to the assigned altitude or flight level. Caution should be exercised both by pilots and controllers to avoid unnecessary ACAS RA involving aircraft at or approaching adjacent altitudes or flight levels.

Suggested Controller's Actions

Best practice embedded in the ASSIST principle could be followed (A - Acknowledge; S - Separate, S - Silence; I - Inform, S - Support, T - Time):

When a pilot reports a manoeuvre induced by an RA the controller should remember the following:

The controller shall not attempt to modify the aircraft flight path until the pilot reports “Clear of Conflict”
The controller shall provide traffic information as appropriate
Pilots are very busy (Increased workload in the cockpit)
TCAS II altitude data is more accurate than radar data
TCAS II evaluates the strength of an RA every second and will change it if necessary

In accordance with PANS-ATM (Procedures for Air Navigation Services - ICAO Doc. 4444, 15.7.3.3), once an aircraft departs from its ATC clearance or instruction in compliance with an RA, or a pilot reports an RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft affected as a direct consequence of the manoeuvre induced by the RA. The controller shall resume responsibility for providing separation for all the affected aircraft when:

the controller acknowledges a report from the flight crew that the aircraft has resumed the current clearance; or
the controller acknowledges a report from the flight crew that the aircraft is resuming the current clearance and issues an alternative clearance which is acknowledged by the flight crew.

Following an RA event, or other significant ACAS event, the pilot and the controller should file an air traffic incident report (AIRPROX). As controller, be ready to provide all necessary details to the pilot’s inquiry on the frequency immediately following the particular RA event.

Based on the provisions of ICAO Doc 4444 (15.7.3.1), the procedures to be applied for the provision of air traffic services to aircraft equipped with TCAS shall be identical to those applicable to non-TCAS equipped aircraft. In particular, the prevention of collisions, the establishment of appropriate separation and the information which might be provided in relation to a conflicting traffic and to possible avoiding action shall conform with the normal ATS procedures and shall exclude consideration of aircraft capabilities dependent on the TCAS equipment.

Procedures in regard to ACAS-equipped aircraft and the phraseology to be used for the notification of manoeuvres in response to a resolution advisory are contained in the PANS-ATM (Doc 4444), Chapters 15 and 12 respectively. The following phraseology is contained in Doc 4444, Para 12.3.1.2

Circumstances following an effective ACAS RA, pilot and controller RTF interchange:

After a flight crew starts to deviate from any ATC clearance or instruction to comply with an ACAS RA:

PILOT: [callsign] TCAS RA;

ATC: [callsign] ROGER;

After the response to an ACAS RA is completed and a return to the ATC clearance or instruction is initiated:

PILOT: [callsign] CLEAR OF CONFLICT, RETURNING TO.. (assigned clearance);

ATC: [callsign] ROGER (or alternative instructions);

After the response to an ACAS RA is completed and the assigned ATC clearance or instruction has been resumed:

PILOT: [callsign] CLEAR OF CONFLICT (assigned clearance) RESUMED;

ATC: [callsign] ROGER (or alternative instructions);

After an ATC clearance or instruction contradictory to the ACAS RA is received, the flight crew will follow the RA and inform ATC directly:

PILOT: [callsign] UNABLE, TCAS RA;

ATC: [callsign] ROGER;

ATCO Actions in Case of Loss of Separation

Responsibility

In the process of ATC provision the controller is responsible for ensuring that separation minima are maintained. A loss of separation (LOS) event requires an adequate action to be taken by the controller in order to resume the established separation and to prevent the situation developing into an accident. When separation has already been, or is in the process of being, lost and the controller perceives a risk of collision, there is no longer an issue of providing standard separation; the essential task is preventing a collision.

Scenarios

There are many hazards associated with incorrect or inadequate avoiding instrucions. In the case of loss of separation and STCA alert, controller actions, delay or lack of action may lead to certain operational hazards such as:

Lack of controller instruction to solve a short-term conflict (lack or absence of action) - The controller does not issue any avoiding instruction, although there is a real short-term conflict with loss of separation.

Late controller instruction to solve a short-term conflict - no TCAS resolution advisory (RA) - The controller issues an avoiding instruction with such a delay that he/she cannot prevent loss of separation, but before a potential TCAS RA is issued.

Avoiding instruction by controller received prior to a TCAS RA and incompatible with the TCAS RA - The controller, unaware of the TCAS RA that the crew is going to receive, issues an avoiding instruction in the opposite direction to the subsequent TCAS RA. The time delay between the avoiding instruction and the RA is sufficient for the pilot to start an avoiding manoeuvre.

Avoiding instruction by controller received simultaneously to a TCAS RA and incompatible with the TCAS RA - The controller, unaware of the imminent TCAS RA, issues an avoiding instruction which is received by the crew at about the same time as the TCAS RA but is in the opposite direction.

Insufficient controller instruction to resolve a short-term conflict - The controller issues an avoiding instruction to resolve a short-term conflict, but the instruction does not allow the aircraft to maintain or restore separation.

Incorrect controller instruction to resolve a short-term conflict - The controller issues a corrective instruction to resolve a short-term conflict, but this leads to a reduction of the safety margins instead of an increase.

Consequences

Consequences of the various possible outcomes of the hazards may be:

a) Minor reduction of separation under control by controller or pilot;

b) Minor reduction of separation with no control by controller nor pilot;

c) Major reduction of separation under control by ATC or pilot;

d) Major reduction in separation with no control by controller nor pilot;

e) Accident.

According to EUROCONTROL Safety and Regulatory Requirement – Risk assessment and Mitigation in ATM (ESARR 4), transposed into Community Law Commission Regulation (EC) No 2096/2005minor reduction in separation is less than half the separation minima.

Defences

It cannot be over-emphasised that each situation must be judged individually. It is not possible to give hard and fast collision avoidance guidance which is universally applicable. A controller is in a very difficult situation when faced with an immediate collision risk and must rely on both general and emergency orientated training when faced with such a scenario. As with any unusual or emergency situation, controllers should exercise their best judgment when dealing with the apparent consequences of loss of separation.

The following list of actions is very general and is universaly accepted, but it is by no means exhaustive:

Assess the situation
Provide adequate reaction
Speak clearly and use standard phraseology
Provide traffic information as appropriate
If an RA manoeuvre is reported and/or observed – do not attempt to modify the aircraft flight path until the pilot reports “Clear of Conflict”
Maintain constant situational awareness of other air traffic – when the problematic situtaion develops, it is a natural human tendency to narrow the attention and focus on the problem
Prioritise actions connected with other traffic as necessary

Communication

The use of standard phraseology and good transmission technique is essential when passing instructions to pilots particularly when timeliness and clarity are important as is the case when passing avoiding action instructions. Any misunderstanding may result in the pilot asking the controller to repeat the instruction, further reducing the time available to execute the avoiding action.

ACAS Procedures

The following procedures referring to aircraft equipped with airborne collision avoidance systems (ACAS) are given in ICAO Doc 4444:

When a pilot reports an ACAS RA, the controller shall not attempt to modify the aircraft flight path until the pilot reports “Clear of Conflict”.

Once an aircraft departs from its ATC clearance or instruction in compliance with an RA, or a pilot reports an RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft affected as a direct consequence of the manoeuvre induced by the RA. The controller shall resume responsibility for providing separation for all the affected aircraft when:

a) the controller acknowledges a report from the flight crew that the aircraft has resumed the current clearance; or

b) the controller acknowledges a report from the flight crew that the aircraft is resuming the current clearance and issues an alternative clearance which is acknowledged by the flight crew.

Automatic Dependent Surveillance Broadcast (ADS-B)

Definition

Automatic Dependent Surveillance Broadcast

Description

ADS-B is a Surveillance technique that relies on aircraft or airport vehicles broadcasting their identity, position and other information derived from on board systems (GNSS etc.). This signal can be captured for surveillance purposes on the ground (ADS-B Out) or on board other aircraft (ADS-B In). The latter will enable airborne traffic situational awareness (ATSAW), spacing, separation and self-separation applications.

ADS-B is automatic because no external stimulus is required; it is dependent because it relies on on-board systems to provide surveillance information to other parties. Finally, the data is broadcast, the originating source has no knowledge of who receives the data and there is no interrogation or two-way contract.

ADS-B is a key enabler of the future ATM Network, contributing to the achievement of the Single European Sky (SES) performance objectives, including safety, capacity, efficiency and environmental sustainability.

The vision for ground Surveillance foresees in en-route and terminal areas the combination of ADS-B with independent Surveillance, the latter provided by Monopulse Secondary Surveillance Radar(MSSR), Mode S or Wide Area Multilateration (WAM). It is noted that WAM system receivers generally include ADS-B functionality.

Airborne ADS-B systems will be available as enablers of the new separation modes. These airborne applications will require changes in the avionics to process and display the air situation picture to the pilot.

For airports, a locally optimised mix of the available technologies, i.e. airport Multilateration, Surface Movement Radars and ADS-B, will enable A-SMGCS systems and integrated airport operations. This could include the availability of Surveillance information on a moving map, using an HMI in the cockpit and in surface vehicles.

The introduction of ADS-B in the Surveillance infrastructure provides important features which can be exploited by the ATM Network:

Full “Network-wide” Surveillance coverage
- Surveillance “everywhere”, i.e. no gaps from gate-to-gate
- Air-to-air Surveillance possible, i.e. traffic situational awareness picture available on board
- The aircraft is integral part of the Network
- Surveillance data provided directly from on-board systems
High performance
Improved safety
Increased capacity
Cost-efficiency
- Reduced cost of the Surveillance infrastructure (ADS-B is cheaper than radar)
- More efficient flight profiles (in areas where previously surveillance was not cost-effective)
- Fuel savings etc.
Environmental sustainability (CO₂ reduction)
Reduced RF pollution (leading to an increased viability of the 1090 MHz datalink)
Global Interoperability
Foundation for future SESAR ATC applications (spacing, separation, self-separation)

ADS-B is currently being implemented in Europe and other areas worldwide (Asia, Australia, Canada, USA).

Global interoperability is ensured at application level and system level. The standards for ADS-B are being jointly developed by EUROCAE and RTCA. Relevant ICAO documentation is also produced.

The 1090 MHz Mode S Extended Squitter technology is used worldwide to ensure global interoperability. At local or regional level other datalink technologies could be used (such as Universal Access Tranceiver UAT in the USA or possibly VDL Mode 4).

The Single European Sky Surveillance Performance and Interoperability Implementing Rule (SPI IR) was approved in July 2011 and will be published in the Official Journal of the European Union in the course of 2011. The SPI IR will require all aircraft operating IFR/GAT in Europe will have to be compliant with Mode S Elementary Surveillance, whilst aircraft with maximum Take-Off Mass greater than 5700kg or maximum cruising True Air Speed greater than 250kts will have to be compliant with Mode S Enhanced Surveillance and “ADS-B out”. The mandate dates are January 2015 for forward fit and December 2017 for retrofit, with further provisions for State aircraft.

The SPI IR will accelerate both the aircraft ADS-B equipage and the ADS-B ground system deployment.

Initial ADS-B Applications

The ADS-B standardisation work is now completed for the initial ADS-B applications, namely all “ADS-B out” and ATSAW applications. It has delivered the Safety, Performance and Interoperability Requirements for:

ADS-B in Non Radar Airspace (ADS-B NRA)
ADS-B in Radar Airspace (ADS-B RAD)
ADS-B for Airport Surface Surveillance (ADS-B APT)
ATSAW In-Trail Procedure in oceanic airspace (ATSAW ITP)
ATSAW Visual Separation in Approach (ATSAW VSA)
ATSAW during Flight Operations (ATSAW AIRB)
ATSAW on the Airport Surface (ATSAW SURF)

In addition, the standardisation of the first spacing application has also been completed with the delivery of the Safety, Performance and Interoperability Requirements for:

Flight Deck Interval Management (ASPA-FIM)

Furthermore, work on the future ADS-B applications (spacing, separation and self-separation) is ongoing or planned by SESAR (Europe) and NEXTGEN (USA). The standards of future applications will be developed also by EUROCAE/RTCA joint work.

Aircraft Equipment

The “ADS-B Out” capability on board is enabled by transponders interfaced with the relevant avionics systems (such as GNSS, pressure altimeters etc.). Many aircraft have ADS-B Extended Squitter capability already available packaged with the Mode S Enhanced Surveillance installations already mandated for core-European airspace.

The “ADS-B In” capability requires a receiver, a processing system (traffic computer) and an HMI unit (often called Cockpit Display of Traffic Information - CDTI). The “ADS-B in” system could be integrated in the Forward Field of view or be in the form of the so-called Electronic Flight Bag (EFB).

The operational use of ADS-B requires certification and operational approval by the regulatory authorities.

Ground Equipment

The ADS-B data transmitted by the aircraft or airport vehicles are received by the ADS-B Ground stations.

In most of the cases, the output of the ADS-B Ground stations will be sent to Surveillance Data Processing and Distribution systems where they are fused with inputs from other possible Surveillance sensors (e.g radars, Multilateration) to create a Traffic Situation Picture for the Users.

ADS-B Data

The ADS-B data transmitted are defined in the relevant standards and certification documents (e.g. EASA AMC 20-24 for ADS-B in Non-Radar Airspace or CS-ACNS for “ADS-B out”). They include (amongst others) the following:

Aircraft horizontal position (latitude/longitude)
Aircraft barometric altitude (will be the same as for the SSR)
Quality indicators
Aircraft identification:
- Unique 24-bit aircraft address
- Aircraft identification
- Mode A code (in the case of CS ACNS for “ADS-B Out”)
Emergency status
SPI (special position indicator) when selected

ADS-B Deployment

ADS-B Deployment in Europe

The deployment of initial ADS-B applications and WAM in Europe is co-ordinated by the EUROCONTROL CASCADE Programme. The ADS-B deployment in Europe is now ongoing in conjunction with WAM deployment and follows three paths:

Voluntary implementation of ADS-B sole means or with WAM in local Non Radar airspace of Europe (“pocket areas”), using currently existing (certified) equipment, from 2011 onwards.
Deployment of WAM and ADS-B systems in Radar Airspace, in which WAM is used first, followed by the use of “ADS-B out”. The latter requires enhanced avionics and is, therefore, driven by the Implementing Rule (SPI IR).
Voluntary implementation of Airborne Traffic Situational Awareness (ATSAW) applications in oceanic areas, starting in the course of 2011.

WAM is already implemented in Armenia, Austria, Czech Republic, Spain and UK (N. Sea). It is noted that due to the integrated ADS-B functionality of WAM systems, the deployment of WAM by ANSPs will enable ADS-B ground station technical functionality.

In addition, WAM and ADS-B deployment is currently ongoing in Germany (WAM by 2012 in Frankfurt, expected to be followed by Munich and Berlin), Portugal (Azores by 2011, WAM/ADS-B), Latvia (WAM by 2011), the Netherlands (N. Sea by 2011, WAM/ADS-B) and Romania (WAM by 2011).

Other ANSPs have implementation plans with target dates of deployment from 2012-13 onwards: Bulgaria (WAM/ADS-B) Cyprus (ADS-B), France (overseas territory, ADS-B), Iceland (ADS-B), Italy (ADS-B), Greece (WAM/ADS-B), Norway (N. Sea, ADS-B), Portugal (WAM/ADS-B), Sweden (WAM/ADS-B) and UK (Scotland, WAM). In addition, UK NATS has included ADS-B with WAM in their Strategy (target date for ADS-B implementation is from 2018).

Airlines have started their certification and operational approval process for ADS-B. Several hundreds of aircraft are already certified for ADS-B operations in Non-Radar Airspace. More than 500 aircraft have received their EASA airworthiness certification, in the context of the CASCADE ADS-B Pioneer airline project.

Implementation based on the SPI Implementing Rule (mandate) covers SSR, Mode S and ADS-B Extended Squitter. This will make airborne installations “future proof”, i.e. supporting all surveillance techniques currently used or planned to be used. The rulemaking will require full compliance with all “ADS-B out” requirements in support of the initial Ground and Airborne Surveillance applications.

In terms of the future ADS-B avionics requirements, the SPI IR will necessitate a transponder upgrade to ED102A/DO260B and a direct GNSS receiver-transponder wiring.

The first aircraft with certified avionics, compliant with the European Commission Implementing Rule, will be available already from late 2011 onwards. The number of aircraft which will be compliant with the Rule will be increased in the next years driven by the mandate dates.

In parallel, “ADS-B in” will be introduced operationally on a voluntary basis from 2011 onwards (in the context of the CASCADE ATSAW Pioneer project) by the ATSAW pioneer airlines (Swiss International Airlines, Virgin Atlantic, Delta, US Airways and British Airways) supported by ISAVIA and UK NATS, driven by the benefits to be acquired. The first applications are the ATSAW during Flight Operations (ATSAW AIRB) and the ATSAW In-Trail Procedure (ITP) over N. Atlantic (Shanwick FIR and Reykjavik FIR). ITP trials are also foreseen in Pacific through a co-operation of FAA with United Airlines.

The issue of establishment and use of a list of aircraft that are approved to receive an operational ADS-B service within Europe will be investigated. The work will actively explore synergies with similar activities worldwide and any needs/opportunities for wider co-ordination.

ADS-B Deployment Outside Europe

In December 2009, Air Services Australia commissioned the ADS-B Upper Airspace Project (UAP), providing ADS-B coverage across the whole continent. Since then, 29 duplicated ADS-B sites have been added, plus a further 14 sites in Tasmania which are associated with the now fully operational Tasman wide area multilateration (WAM) system. Aircraft avionics are being assessed and approved for operational use. ADS-B data from non-approved aircraft is filtered out at each site. Currently, over 1200 airframes are approved and receiving the operational and safety benefits of ADS-B services in Australia. Australia has also made ADS-B equipage mandatory for all aircraft (domestic and foreign) operating at or above FL290 as from December 2013.

Automatic Dependent Surveillance-Broadcast (ADS-B) brought surveillance coverage for the first time to 250,000 square nautical miles of airspace over Hudson Bay in Northern Canada. The majority of the flights in this airspace link Europe and North America, while many transit to Asia, including those using polar tracks. Service commenced in January 2009. Controllers currently use ADS-B tactically by applying reduced separation between equipped aircraft on an opportunity basis. This means each aircraft will have the appropriate protected airspace around it applied based on its capability. The subsequent step for NAV CANADA is to segregate airspace vertically, ADS-B deployment is also ongoing by the US FAA, enabled by two datalinks, i.e. 1090 MHz ES and UAT. The U.S. ADS-B Final Rule will require aircraft that operate above FL180 to broadcast on the 1090ES link The FAA is not prescribing the choice of link for aircraft flying below FL180; both links are supported and operators are free to choose whichever link meets their needs. Aircraft broadcasts go to other aircraft and to ground radio stations, where the information is processed and displayed to controllers. Where available, information from FAA radars is combined with ADS-B data to support ATC separation services. In May 2010, the U.S. ADS-B Final Rule was published, requiring ADS-B Out equipage in U.S. airspace where a transponder is currently required, with compliance by 1 Jan 2020.

ADS-B deployment is also being undertaken in other regions worldwide (such as Indonesia).

Parallel Runway Operation

Objective

The main objective of implementing simultaneous operations on parallel or near-parallel runways is to increase runway capacity and aerodrome flexibility. The largest increase in overall capacity often includes the use of independent approaches to parallel or near-parallel runways.

The safety of parallel runway operations in controlled airspace is affected by several factors such as the accuracy and use of the associated radar monitoring system, the effectiveness of the process of controller intervention when an aircraft deviates from the correct ILS localiser or RNAV course and the precision with which aircraft can and do fly the approach.

Modes of Operation

In ATC terms, the various modes of operation available for the use of parallel or near-parallel instrument runways are distinguished as:

Simultaneous parallel approaches

Mode 1, independent parallel approaches: simultaneous approaches to parallel instrument runways where radar separation minima are not prescribed between aircraft using adjacent ILS; and
Mode 2, dependent parallel approaches: simultaneous approaches to parallel instrument runways where radar separation minima between aircraft using adjacent ILS are prescribed.

Simultaneous parallel departures

Mode 3, independent parallel departures: simultaneous departures for aircraft departing in the same direction from parallel runways.

It should be noted that when the spacing between two parallel runways is lower than the specified value determined by wake turbulence considerations, the runways are considered as a single runway with regard to vortex wake separation.

Segregated parallel approaches/departures

Mode 4, segregated parallel operations: simultaneous operations on parallel runways where one runway is used for approaches and landings, and one runway is used for departures.

In the case of segregated parallel approaches and departures there may be semi-mixed modes of operations.

Semi-mixed parallel operations

One runway is used exclusively for approaches while approaches are being made to the other runway, or departures are in progress on the other runway.
One runway is used exclusively for departures while other is used for both departures and arrivals.

Mixed mode parallel operations

At least one runway is used for both take offs and landings.

Factors Affecting Simultaneous Operations on Parallel Instrument Runways

Factors which may have an impact on the maximum capacity or the desirability of operating parallel runways simultaneously are not limited to runway considerations. Taxiway layout and the position of passenger terminals with reference to the runways may make it necessary for traffic to cross active runways, a situation which may not only lead to delays but also to a decrease of the safety level due to the possibility of runway incursions by either arriving or departing aircrsft.

Factors to Consider When Determining the Mode of Operations

Theoretical studies and practical examples indicate that maximum aerodrome capacities can be achieved by using parallel runways in a mixed mode of operation. In many cases, however, other factors such as the land-side/air-side infrastructure, the mix of aircraft types, and environmental considerations result in a lower achievable capacity.

Other factors such as non-availability of landing aids on one of the parallel runways or restricted runway lengths may preclude the conducting of mixed operations at a particular aerodrome.

Because of these constraints, maximum runway capacity may, in some cases, only be achieved by adopting a fully segregated mode of operation, i.e. one runway is used exclusively for landings while the other is used exclusively for departures.

The advantages to be gained from segregated parallel operations as compared to mixed parallel operations are as follows:

a) separate monitoring controllers are not required;

b) no interaction between arriving and departing aircraft on the same runway and a possible reduction in the number of missed approaches;

c) a less complex ATC environment overall for both radar approach controllers and aerodrome controllers; and

d) a reduced possibility of pilot error following undetected selection of the wrong ILS.

Operational Issues

Parallel Runway Operation need to be carefully managed in such a manner as to minimise the risk of runway incursion or wrong runway use due. Closely-spaced parallel runways may affect the pilots' situational awareness or lead to their distraction or confusion.

A potential problem with close parallel runway spacing is the possibility that an aircraft may make an approach to the wrong runway. Two scenarios can be considered:

Pilot SOPs for approach clearance acceptance and subsequent setting of the required navigation equipment should be robust and attract 100% compliance. The role of the PM (and if present the augmenting crew occupying supernumerary seats) in a multi crew flight deck in cross checking that correct actions are taken is crucial.
If a pilot cleared for an instrument approach acquires visual reference with the aerodrome when some distance from landing, it is possible in the absence of the right level of crew discipline and interaction for alignment with the wrong runway to follow.

Safety-Related Issues Affecting Independent Approaches to Closely-Spaced Parallel Instrument Runways

Independent operations on closely-spaced parallel runways are significantly safety critical and should be used only after a proper risk assessment has been undertaken. In this process, the issues listed below, which are contained in ICAO Doc 9643 Manual on Simultaneous Operations on Parallel or near parallel Instrument Runways (SOIR), should be considered:

a) weather limitations — independent instrument approaches to parallel runways spaced by less than 1,525 m but not less than 1,035 m between centre lines should, as prescribed by the appropriate ATS authority, be suspended under certain adverse weather conditions including windshear, turbulence, downdrafts, crosswind and severe weather such as thunderstorms, which might increase ILS localiser deviations to the extent that safety may be impaired and/or an unacceptable number of deviation alerts would be generated;

b) ILS flight technical error — the track of aircraft using the ILS localiser course is subject to errors from several sources, including the accuracy of the signal, the accuracy of the airborne equipment, and the ability of the pilot or autopilot to follow the navigational guidance (flight technical error (FTE)). Deviations from the ILS localiser course may vary with the runway under consideration; it is therefore essential that the FTE is measured at each installation and the procedures adapted to ensure that false deviation alerts are kept to a minimum;

c) communications — when there is a large deviation from the final approach track, communication between controllers and pilots involved is critical. For independent parallel approaches two aerodrome controllers are required, one for each runway, with separate aerodrome control frequencies;

d) obstacle evaluation — since aircraft may need to be turned away from the final approach track at any point during the approach, an obstacle survey and evaluation must be completed for the area opposite the other parallel runway; this is necessary in order to safeguard early turns made to avoid potential penetration of the adjacent final approach;

e) pilot training — operators should ensure that flight crews conducting simultaneous independent approaches to parallel runways are familiar with the issues that arise. It should be noted that if an immediate missed approach is instrucyted by ATC, the required manoeuvres may differ from the promulgated standard missed approach;

f) controller training — training is required for air traffic controllers prior to being assigned monitoring duties. This training should include instructions in the specific duties required of a monitoring radar controller.

g) risk analysis — a risk analysis using available data should indicate that the probability of having a miss distance of less than 150 m (500 ft) between aircraft is expected to be less than 1 per 56,000,000 approaches. Wherever independent approaches to closely-spaced parallel runways are envisaged, a risk analysis must be completed for each location to ensure satisfactory levels of safety;

h) airborne collision avoidance system (ACAS) — during operational evaluations of ACAS II, some unnecessary missed approaches occurred as a result of “nuisance” resolution advisories (RAs). To remedy this situation, a number of modifications were made to the collision avoidance logic. However, these modifications did not completely eliminate such occurrences. Accordingly, the use of “traffic advisory (TA) only” mode during parallel approach operations should be recommended and indicated on the published approach charts;

i) transponder failure — If an aircraft without an operating transponder arrives at an aerodrome, ATC will have to create a gap in the arrival flow so that the aircraft will not require monitoring. If an aircraft transponder fails during an instrument approach, the monitoring radar controller will instruct any adjacent aircraft to cancel their approach;

j) fast/slow aircraft — if a fast aircraft deviates towards a slower aircraft on the adjacent approach, the slower aircraft may not be able to move away quickly enough to assure safe spacing. ATC must create a gap in the arrival flow to safeguard the approaches of slower aircraft;

k) approach chart notation — the charts showing instrument approach procedures to runways used for simultaneous parallel instrument operations should indicate such operations, particularly using the term “closely-spaced parallel runways”. The terminology should be reflected in the title of the approach chart including the runway identification;

l) unnecessary cancelled approaches — an unnecessary cancelled approach is a situation in which the monitoring radar controller initiates a cancelling approach and the deviating aircraft subsequently remains in the normal operating zone (NOZ). The number of alerts, both true and false, should be monitored as a method of assessing the performance of the system. It may be necessary to amend the parameters of the alerting mechanism if too many false alerts are experienced; and

m) autopilots — older nodels of autopilots provide mean a higher FTE. Modern autopilots are nuch more acccurate and their FTE is less.

Safety-Related Issues Affecting Dependent Approaches to Closely-Spaced Parallel Instrument Runways

The minimum spacing between two aircraft in the event of a deviation is calculated using techniques similar to those used for independent parallel approaches.

Two factors apply:

since the radar separation is applied diagonally, less distance between runways means a greater in-trail distance between the aircraft; and
less distance between runways also means that the deviating aircraft crosses the adjacent approach track more quickly.

Near-Parallel Runways

Near-parallel runways are non-intersecting runways whose extended centre lines have an angle of convergence/divergence of 15 degrees or less.

No special procedures have been developed as yet for simultaneous operations to near-parallel runways. Each situation is considered on a case-by-case basis and is dependent on a number of variable conditions.

New Concepts and Procedures

In order to maximise the capacity there are some concepts such as High Approach Landing System (HALS) that were developed and deployed (for a given period of time only) to allow aircraft to land simultaneously on closely spaced parallel runways at Frankfurt Airport. The concept involved adopting a second, strongly displaced landing threshold for the southern runway to mitigate against wake turbulence by flying above the vortices of the leading aircraft.