Head Up Display for ATC

A radical solution for air traffic control systems at airports

The design of Air Traffic Control systems have become increasingly dependent upon the development of the display of electronic data together with the associated tools to provide enhanced safety and traffic handling capacity. For the Area Control Centres and the Approach Control units, the radar screen is being replaced with an integrated data display depicting both radar and flight data derived information. Similar functionalities are now being developed for the Control Tower task where the controller is to be provided with electronic screens that are to replace the traditional flight progress strip.

This article discusses the development of a Head Up Display for Tower Controllers. This head-mounted display would enable the controller to see and interact with the electronic data. The data would overlay the real world and whilst some of the data would be fixed to the normal vision, certain data would be fixed in space and only be visible when looking in a specific direction. Further development will lead to a binocular HUD where 3D imaging will be used.

SAL Consultants, a member of the British Airports Group, and the originators of the concept are actively developing the operational requirements associated with this unique tool.

The Tower Control Task

The traditional task of the Control Tower controller has been in visually tracking and controlling aircraft and vehicles on much of the airport and providing a safe and expeditious usage of the runways for the departing and arriving aircraft. In providing this service, the controller has the use of the flight progress strip upon which the details of the individual aircraft are displayed and updated. In using the strips, the controller will often place the appropriate strip in the runway bay of the strip board to denote the runway being occupied, the coordination between the Approach controllers and the tower being achieved verbally on the telephone.

These traditional methods relied upon verbal coordination and visual control of the airport traffic; the new systems have endeavoured to overcome the coordination problem by incorporating electronic flight data in the Tower console. The driving force behind this was to ensure that any modification to the flight data was available to all interested parties associated with that particular flight. Thus the updating of times together with the provision of clearances permitted an increased efficiency of operation.

Further developments are being seen as more sophisticated tools become available where data are shared between the aircraft and the ATC service. Data link is being developed in order to reduce the reliance upon the radio exchanges and to improve the accuracy of the information transmitted and received.

The increased use of electronic data for accurate position information together with increasing use of air/ground data link will have a profound effect upon the Tower controllers’ traditional role.

The Approaching Problem

Data displayed upon electronic screens have been founded upon a basic concept – the person using them is continually monitoring them and scanning for updates. Whereas this is mainly true for the Enroute and Approach control functions, it is entirely inappropriate for the Tower controller whose primary function is visually monitoring the traffic both on and in the immediate airspace surrounding the airport. This can be seen where an airfield has to operate under difficult visibility conditions, even in conditions where aircraft are landing blind. The capacity of the airport is severely reduced and a significant proportion of this capacity shortfall is due to the controller’s inability to see the aircraft and vehicles.

Much of the research into airport capacity is aimed at reducing the effect of poor visibility upon the traffic since the recovery times requiring rescheduling and repositioning can cost the airlines a considerable financial loss. Any improvements thus provided by new methods and tools are therefore to be welcomed.

Data Displays

From the above it can be seen that there is a strong link between safety, capacity and operating costs with the drive to develop sophisticated electronic tools for the Control Tower.

Presuming that there are to be increasing requirements for data displays in the Tower, what are the constraints?

The Control Tower personnel operate in full bright sunlight, and in the night operations, almost in complete darkness to permit improved night vision. Electronic data displays must therefore be capable of being efficiently seen in this changing and challenging variation of ambient lighting. Anyone who has tried to view television when the sun is shining on the screen will understand the engineering problem.

The usage of the duty runway is determined by the responsible controller and other members of the team will request permission to cross or to approve works/inspections adjacent to the runway. The traditional method was to block the runway segment of the flight strip board with a strip. This was a very powerful and safe means to highlight to the controller that the runway was blocked. Figures related to runway incursions have demonstrated that a very powerful "runway occupied" highlight is essential to the safe operation of the airfield. How is this to be achieved electronically?

A Unique Solution

Over the past few years, developments in the area of HUDs have led to a display that completely answers the operational requirement for Control Tower operation. Unlike other forms of HUD, this does not have a screen or projection system. The requirements are that the display must be readable in all ambient light conditions, from full sunlight to absolute darkness. The equipment must be light and comfortable to wear throughout the shift and be safe to use over a period of years. The data provided to the controller must be fail-soft insofar as having alternative data sources available.

Microvision of Seattle, USA, manufactures the display hardware; and is unique since the data is written directly onto the retina of the eye as a stream of photons. It can be likened to the television screen where the electron gun sweeps the phosphor of the screen where due to persistence a picture is formed. Precisely the same happens with the eye’s retina since there is a natural persistence allowing a picture to be built. Since the pupil of the eye contracts in bright sunlight to lessen the light impinging on the retina, and since the photon stream still penetrates, the reduction of data contrast is minimised. The result is a virtual overlay of the real world, the controller no longer needing to view data inside the Tower, but able to devote attention on the work area – outside.

Application Methodology

There are three categories of data that can be displayed. Data that are needed in the vision all the time, data needed only when looking in a certain direction and data attached to moving targets.

The first category covering permanently available data could cover warnings together with high and low level alarms telephone calls etc.

The second category covers data associated with a certain area or direction. This is known as contextual data and could be displayed according to direction of sight. When looking at the threshold of the runway assigned as the landing runway, then a distance from touchdown display together with the associated aircraft data. When looking at the apron area, data could be displayed related to stand numbers and the associated aircraft data. It should be mentioned that when looking at the runway threshold where no traffic is on final, then no display is shown.

The third category will, in future be dependant upon using both eyes to provide a three dimensional picture. Initially this would display labels attached to aircraft and vehicles, similar in many ways to the labels used on the radar displays.

Information Path

Airport traffic can be seen as a flow of data. For aircraft departing, there is an almost rigid process. Starting with the flight plan being pre-activated, the request for push-back and start up, the taxi request, the receipt of airways and departure clearance, the permission for departure and the transfer to the next controller. For arriving aircraft, it is similar, starting the process with the receipt of the flight details, the coordination process (distance to run), the request for landing clearance, the arrival with taxi instructions to apron and stand number. The above is a simplistic overview, but demonstrates the steps that occur as a repetition.

This process can provide the basis for a data display where data provided are coded and only displayed where and when required.

Data Category (Fixed view)

These data are permanently in vision and are intended to be warning information that will highlight directly in the controller’s view no matter where the controller is looking. This can be particularly useful for runway incursion alerts, coordination requests and meteorological warnings etc.

At this early stage of development, all data are viewed permanently whilst the head movement sensors and their associated software is refined. We hope to develop a demonstration tool by the end of this year. Figure 2 above shows the background as black and foreground as white. Within the HUD, black equals zero light and white 100% light, thus the black denotes the transparent see-through areas of the display.

Data Category (Contextual)

This category is the primary development area for the near future. We will be identifying the data display needs for existing Radar and Flight Data Processing Systems. The HUD data will be based upon these data already available in the Tower thus enabling our system to be integrated into a Tower simulator as an initial stage in the operational development and approval process.

Data Category (3D)

These data are dependent upon further hardware development. It is intended to develop the functionality to provide labels attached to aircraft, both in the air and on the ground.

At this stage, we will be looking at vision augmentation in periods of poor visibility where the controller will be enabled to see through fog to provide a safe and efficient service.

Conclusion

We remain sensitive to the need to develop within our current systems capabilities and to listen to the controllers in developing this tool. We are convinced that the new tools and systems being developed, viz A-SMGCS are essential for future capacity handling, but we are not convinced that the controller’s attention should be taken away from the primary work area – outside.

Subject to our success in developing suitable demonstration software, SAL will be showing this unique display at ATC Maastricht next February on stand 345.

The figure below was where we started with the prototype.

Figure 3 shows some initial thoughts for the display. It provides wind velocity with the two dials, QNH, a distance from touchdown from 20nm with three aircraft and another three departures beside the runway representation.

We should stress that this was the first prototype and that integrated circuits and silicon wafer technology has enabled the company to significantly reduce the size. It should be noted that further reduction in size is being developed for use on a mobile phone.

Figure 4 – Nomad © Microvision

Fig 5 An artists impression using the previous version of NOMAD © SAL Consultants