NZALPA was recently invited to provide feedback by way of submission to Airways Corporation on their replacement options for the Auckland Tower. The current Tower at Auckland Airport was originally commissioned in the 1960’s and is now in need of significant maintenance and repair. It is also reaching the end of its lease with Auckland Airport Limited.

The Airways’ proposal included the option of using a digital solution by way of a Remote Aerodrome Air Traffic Service (ATS) – i.e., a digital tower. 

The concept of remote aerodrome ATS enables provision of aerodrome ATS from locations/facilities without direct visual observation. Instead, provision of ATS is based on a view of the aerodrome and its vicinity through means of digital technology.

A remote tower can be located away from the aerodrome it is providing a service to, or it can be located in a building on or close to the aerodrome, but without an adequate direct view of the area of responsibility. It must, however, achieve the same – or better – situational awareness and level of safety in accordance with the provision of international standards (namely the International Civil Aviation Organisation (ICAO) Documents 4444 and 9426).

The concept was initially introduced and developed in Europe in the early 2000s and has been further developed and refined over time.

The first implementation of a remote tower, providing aerodrome ATS based on a situational awareness fully in accordance with ICAO Documents 4444 and 9426, was approved by the European Union Aviation Safety Agency (EASA) and introduced into operations in Sweden in 2015.

There are now a small number of remote digital towers – all of which operate at small, low-density aerodromes with movements of 40 or less per day.

The concept of remote aerodrome ATS is not without its limitations. However, it is constantly evolving and with the gaining of operational experience and technological advancements, along with new applications, the concept will be further refined and improved over time.

NZALPA supports digital tower technology. However, it is NZALPA’s view that digital remote towers are only suitable at this point in time for locations that are (a) physically remote, (b) have a low air traffic footprint and (c) have no major terrain, geographic or meteorological obstacles in the vicinity of the aerodrome. In other words, they are best suited to small regional airports in New Zealand.

NZALPA accepts that digital technology that utilises fixed camera arrays and pan-tilt-zoom camera, cables/fibre, WLAN/LAN communication equipment, video processing/transmission systems and video screens has definite advantages, but these come with an associated increase in complexity and risk.

One critical parameter is the time delay between the occurrence of an event in the real world and its presentation to the air traffic controller (ATCO) or aerodrome flight information service officer (AFISO) on the visual presentation/binocular functionality (referred to as video latency).

The fidelity of the image presented to the ATCO or AFISO also depends on the video update ‘frame rate’ – defined as the number of times per second the video is updated. The video update rate primarily affects the following operational aspects of the presented image:

• the appearance of moving objects (such as aircraft or vehicles) i.e., if a smooth and regular impression to the human eye is provided;

• the capability to perceive and monitor flashing/rotating objects (such as runway guard lights (RGL), aircraft strobe lights, emergency vehicle lights or rotating propellers/rotors); and

• the ability to perceive acceleration/ deceleration/direction changes (i.e., turns) of moving objects.

Also, validation activities have shown that the presented image in some technical platforms may appear brighter compared to the real-world conditions during dusk and dawn, prolonging the experience of daylight and enabling the ATCO/AFISO to see occurrences which are not possible to be seen in real life due to darkness conditions. However, a pilot may be experiencing a significantly darker environment.

It may also be difficult for the ATCO/ AFISO to judge when darkness has occurred, potentially leading to incorrect service provision or incorrect selection of airfield lighting.

Equally, the image in true darkness may be optimised for a less noisy image to compensate for artificial light, but this could mean that meteorological elements may be harder to detect. As the cameras change the light conditions of the outside view, it is necessary for the ATCO/AFISO to get information about real-time realistic light conditions somewhere from the controller working position.

ICAO Document 4444 states: “prior to take off aircraft shall be advised of significant meteorological conditions in the take-off and climb-out area.” Therefore, the visual surveillance system needs to enable the ATCO/ AFISO to visually observe some significant meteorological conditions in the take-off and climb-out area (such as the type of, and distance to, the significant weather, the daylight/ darkness conditions as well as the meteorological visibility) which would be difficult if sitting 500km away!

One aspect of the complexity and risk that arises in relation to digital towers is their reliance on fibre optic and microwave links to communicate between the camera masts and the digital tower module (DTM). Previous events have demonstrated that there are vulnerabilities that arise in a New Zealand environment relying on underground cables to provide communication or other infrastructure links.

Bandwidth via either microwave of fibreoptic cables can be an issue. The remote tower system should enable the ATCO/AFISO to detect any failure or irregularity which could adversely affect the safety or efficiency of flight operations and/or the provision of ATS, such as corrupt, delayed (beyond the defined maximum latency value) or frozen image of the visual surveillance system. At times where large public events such as sports games or concerts are held nearby, bandwidth can be severely compromised.

Remote digital towers allow for more than one aerodrome to be provided with ATS from the same facility. A potential issue with this would be the filing of alternate aerodromes in flight plans. If the destination aerodrome and all alternate aerodromes, filed in one flight plan, are part of one remote tower centre (RTC), a possible failure of the RTC could affect the availability of ATS at all those aerodromes. If airspace users are not aware of the interdependencies between those aerodromes, a hazardous situation can occur as ATS would not be available at any of the airports selected in the flight plans.

Furthermore, ICAO Annex 14 states that the remote tower infrastructure should allow the ATCO/AFISO to communicate via a signalling lamp (e.g. in the case of radiotelephony or data link communication failure). The remote operation of the signalling lamp might be subject to delays due to communication latency from the remote facility to the aerodrome infrastructure and a pilot may not know where to look for a signalling lamp should no physical tower be present.

In closing, NZALPA recognises the benefits of digital towers at appropriate locations. However, we also insist on the need for phased trials of digital towers at appropriate and safe locations. Improved safety and efficiency, and not just cost savings, would need to be demonstrated before the implementation of even a hybrid tower using digital technology.