Towering dilemma

Difficult decisions face ANSPs when they need to establish a control tower service or when traffic levels do not warrant retaining a full one. Setting up a new service means a sizeable investment in buildings and technology and buildings and equipment need to be maintained, upgraded and sometimes replaced.

As an example, Airservices Australia is the midst of a major undertaking to build new control towers and upgrade others over 28 locations. The capital cost — about $90 million.

New services also means air traffic control staff need to be relocated but moving them to remote locations is often costly and difficult. Issues over control tower construction and staff relocation have recently arisen for Airservices at Karratha and Broome, Western Australia.

Tower services are needed for growing resources sector FIFO traffic and another is being considered Port Hedland. But at a conservative estimate, at least 18 months is needed to commission a new control tower and staff it at an existing airport.

In the case of an airport with low traffic, there are few alternatives to cut operational costs other than by lowering operating hours or closing the service. However, implementing reduced coverage often raises questions about the necessity of the service.

Regular public transport (RPT) operations may take place outside core service hours, making it more difficult for the air traffic service unit to be self-supporting for staff leave, training and administration. And over time traffic patterns can change, with airports that seemingly did not need a control tower service once again crying out for one. But decommissioned operations can be time-consuming and costly to resurrect.

So let’s look at Sweden, the leader in remote tower technology. All Swedish airports with RPT operations must have a control tower service but traffic levels at some airports are low, often with long intervals between aircraft movements.

Swedish ANSP Luftfartsverket (LFV), which wanted to improve operational efficiency, made an agreement with Saab to jointly develop and market remote tower technology.

The concept involves capturing vision of the airport and surrounding airspace with video cameras mounted on a mast. Images are compressed then sent by fibre optic cable to a control room at the central site, where they are displayed on video screens.

Typically, screens are positioned in an arc spanning 270 deg to display a 360-degree picture of the airport and surrounding airspace. This enables staff to easily move in and out of the operational area, rather than having screens completely circling the air traffic controllers.

Early evaluation at LFV’s Ängelholm test facility found controllers had difficulty with depth of view and judging spacing between aircraft. These issues were overcome by using more and higher-resolution cameras and screens and increasing the video frame rate.

Saab and LFV ran an operational trial In 2009, providing remote control tower services for Ängelholm from a control room at Malmo Airport, about 100km distant. The trial found that the video signal could go be compressed and decompressed and still be good enough for aircraft control.

There were unexpected problems: birds began to nest amongst the mounted cameras. Rain, bird impacts and insects dirtied the camera lenses but these have all been overcome. The initial trial used a 360-degree visual tower simulator display and subsequent development has utilised off-the-shelf LCD screens.

Saab and LFV are now bringing remote tower technology into full operation with control of Sundsvall-Härnösand and Örnsköldsvik Airports from Sundsvall due to begin early in 2013.

To test the applicability of the remote tower concept, Airservices is running an operational trial at Alice Springs. An agreement between Airservices, Saab and LFV has been signed to assess the Swedish technology under Australian conditions. The system will be a derivative of the development being commissioned at Sundsvall-Härnösand and Örnsköldsvik Airports.

Control of Alice Springs aerodrome and approach traffic will come from Adelaide Airport. Airservices Program Director Craig Deitch explains: “We want to evaluate an existing site that does not involve surveillance displays or electronic flight progress strips. The trial is focused on evaluating whether the visual component of the control tower service can be undertaken from a remote location.”

The visual image of Alice Springs aerodrome and its traffic will be captured by 14 fixed cameras mounted on a mast to provide a 360-degree picture. A rotating pan/tilt/zoom camera, controlled selectively by the air traffic controllers, enables specific features to be more closely examined.

The four-month trial is due to begin next February. Alice Springs is a moderate to low- density airport with up to 10 aircraft on the control tower frequency at once. It has a 50 per cent mix of IFR and VFR operations encompassing helicopters and light aircraft through to C17 and B737 scheduled services.

The trial will begin with low traffic periods then progress to the busiest times of the day. Two air traffic and a tower controller as well as a coordinator will provide the service from Adelaide, a similar staff configuration to that at Alice Springs. Another controller will be on site at Alice Springs to monitor traffic and will assume responsibility immediately if there’s a communications link failure.

Success of the concept will be determined by assessing staff ability to control traffic remotely using screens compared with being on-site in a control tower. Mr Deitch says: “There needs to be no degradation in the ability of the air traffic controllers to handle traffic. In essence, we will assess whether controllers, operating remotely, can provide visual separation and have the same level of confidence to use the suite of separation techniques and equipment.”

Staff performance assessments will take place periodically during the trial, reviewing the performance of each controller and determining whether their performance is being impaired by using the remote technology equipment. It also will track whether their work performance changes.

Visual separation is the main way tower controllers sequence and separate aircraft around an airport. A number of academic human factors studies have been done to identify key elements of this technique and whether they can be used in a synthetic environment.

A key challenge is whether technology can replicate the visual movement of aircraft sufficiently to enable controllers to recognise speed differential and anticipate separation between aircraft.

Judgement of aircraft approaching the airport and operating in the circuit is an essential element of the tower controller’s role, providing separation and enabling the airport to maximise its operational capacity. At regional airports, separation based on visually sighting aircraft typically is not aided by electronic surveillance.

Alongside the assessment of controller’s operational capabilities a technological evaluation and safety and business cases also will be used to evaluate the remote tower technology.

Australia’s vastness presents technological and cost challenges in taking visual images from a remote airport to the central control site. The direct distance between Alice Springs and Adelaide is 1,500km, significantly greater than the distance involved in the Swedish trial.

Fibre optic bandwidth must be secured for the transfer of visual images. A delay of less than a second is expected between an event in Alice Springs and its image appearing on the screens at Adelaide, so no material impact is expected in viewing the video image.

Video tracking software will be included as part of the trial. It puts a track box around any object detected flying over a pre-determined airspeed. The video information is linked to the flight data processing system to assign a track number to the box.

This gives two significant advantages to enhance the air traffic controller’s situational awareness: the track box remains with the aircraft as it approaches the airport so there is no need for the controller to search the sky to find the aircraft and confirm its identity. And maintaining the aircraft’s identity on the screen promotes a head-up display, reducing the controller’s need to leave the visual picture.

The capital cost of equipment for remote tower operations is relatively small — much less than the cost of building new facilities. But the rental cost of fibre optic bandwidth from Alice Springs to Adelaide is sizeable and there are concerns this cost may impact negatively on the business case. However, as well as technology for the trial, Saab will provide supporting information for the business and safety cases

Remote tower technology has possibilities in Australia and internationally to improve the cost effectiveness and responsiveness of control tower operations. But the imperative to introduce it is different in Australia.

At the moment, we need to quickly implement control tower services at remote locations. The nature of traffic growth at remote airports, based on FIFO services for the resources sector, may mean a corresponding sharp decrease in aircraft movements should this industry decline or become mature.

Remote tower technology enables traffic growth to be addressed relatively quickly without the need for large, time-consuming capital investment. Relocation of staff is not necessary so services can be downsized relatively easily should traffic decline.

In comparison, Europe has an imperative to obtain control tower efficiencies by centralising the workforce. A concentration in providing services to RPT aircraft means workload can be planned, enabling a centralised facility to provide control tower services at more than one location.

This prospect will depend on the volume and complexity of traffic. If a controller has to look at the traffic pattern of two airports simultaneously or continually switch airport images, then controlling several airports is unrealistic.

However, if there are relatively few scheduled RPT movements throughout the day and a control tower service is not warranted by local general aviation activity, a remote service could be used during specific periods. If this model is adopted multiple airports could be controlled centrally and may have applications in countries such as New Zealand.

Remote tower technology may provide options to improve traffic handling capabilities and efficiency. Digitising the images of aircraft and vehicles at an airport enables vision enhancement for the air traffic controller. Importantly, the aircraft image can be enhanced in poor weather conditions to aid visual separation.

Anomaly detection software that compares a baseline picture with video can be used to prevent runway incursion or identify other irregular aircraft operation. The remote tower technology also enables a heads-up display of information for the air traffic controllers. Enhanced situation awareness means controllers can watch traffic for longer periods without having to seek information heads-down
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This technology also has been shown to provide improved controller training opportunities as well as being able to replay traffic situations when investigating incidents or accidents.

Although the initial focus for remote tower technology has been for low to medium-density regional airports, it’s also being introduced at international airports, where use includes providing contingency control tower services, observation of areas on an airport that cannot be seen from the control tower and possibly as an alternative to surface movement primary radar.

Britain’s National Air Traffic Services (NATS) has set up a virtual contingency facility (VCF) for London Heathrow. Located off-airport. it will provide control tower services if the main facility goes down. According to Jane’s, the VCF will be able to maintain operations at 70 per cent of Heathrow’s normal traffic capacity should it be required to be used.

Germany’s Deutsche Flugsicherung (DFS) uses video sensors at Cologne for control tower vision of a taxiway obstructed by an airport warehouse development. Based on the project at Cologne, DFS has been evaluating whether remote tower technology could be used for distant tower operations at large airports.

This may avoid the need to build a second tower at Munich as part of development of its third runway. DFS is developing this technology and expects to implement it in some form at up to six international airports by 2016.

Remote tower technology also can supplement the surveillance information of ground traffic supplied by primary radar and multilateration, a navigation technique based on the measurement of the difference in distance to two or more stations at known locations that broadcast signals at known times.

A technological interface between traditional ground surveillance sources and video information can be developed to present all movements synthetically to tower controllers. Linking flight plan data to the video image enables tracking information to be displayed with the video image.

This use of video could partly replace primary surface movement radar. Video presents information about weather and abnormal operating conditions, such as fire, that cannot be detected by primary radar.

As part of the Airservices’ tower upgrade program, new technology progressively is being commissioned in both international and regional control towers. In the future video information could be fused with other ATM data, such as flight plan track, ADS-B and radar, in the INTAS control tower technology system. Service contingency and visual obstruction issues, addressed by other countries, also could be introduced in Australia.

Remote tower technology is still in the early stages of its development. Expect to see variants to progressively enter operation, as it means air traffic control organisations can respond more swiftly to changes in service requirements and cut the costs of control tower operations at regional airports. And as a bonus, it also has the potential to provide service enhancements at international airports.