Ground lighting at LGW

London Gatwick is the world’s busiest single runway airport in the world and therefore values the smooth running and maintenance of its lighting systems, writes Tim Hardy.

London Gatwick Airport (LGW) began life in 1930 as a small flying club (Surrey Aero Club) when the owner, Ronald Walters, obtained his first flying licence. By May 1936 passengers were boarding the first scheduled service from Gatwick to Paris, with routes developing throughout that year to include Malmo via Amsterdam, Hamburg, Copenhagen and the Isle of Wight from Gatwick.

LGW is now the busiest single runway in the world, the second largest airport in the UK and the sixth busiest international airport in the world, with over 250,000 air transport movements a year. Gatwick serves over 200 destinations, with around 90 airlines currently operating from the airport. It handles more than 31 million passengers a year, a figure which is forecast to rise to around 40 million by around 2012/13. BAA is investing almost £800 million into the airport’s infrastructure over the next ten years to improve the customer experience and to maximise the use of its single runway, two terminal operation.

UK regulation and standards

The lighting requirements for an airport such as Gatwick, which operates 24 hours a day, includes low visibility operations which are specified by the regulatory body the Civil Aviation Authority (CAA) under the Safety Regulation Group (SRG) in CAP 168. Under the conditions of its aerodrome licence, LGW must comply with requirements in terms of operational management, planning, safety and any developmental work on the airfield.

The Aeronautical Ground Lighting (AGL) services at the airport are operated by National Air Traffic Services, (NATS), but Gatwick Airport remains responsible for providing the control and for monitoring the system. The AGL control system enables air traffic controllers to remotely operate AGL services from the control tower’s visual control room.\

As far as NATS are concerned, it is imperative that a number of facilities are provided by the airport operator to fulfil the requirements for a safe and competent air traffic service. Some of these requirements include:

• An approach and runway lighting system compliant with CAP 168
• An ability to switch individual lighting services easily and quickly to match changing weather conditions
• An ability to select brilliancy settings for the services including the ability to change brilliances as requested by a pilot
• Ability to see with ease which services are selected from a lighting panel
• Ability to see with ease the status of services and for the lighting panel to indicate any unserviceable issues
• Ability to see with ease if there are any faults within the control system by the slue of alarm indications.

The AGL system

Aeronautical Ground Lighting (AGL) is used to indicate to pilots the position and status of the runway and to guide aircraft from the runway to the terminal buildings. The lighting is designed to act as an indicator for the pilots, rather than illuminating a particular area on the airfield.

Runway lighting consists of two basic areas, approach lighting and runway surface lighting. Approach lighting can be viewed by a pilot from a considerable distance and provides a visual reference to the location of the airport, the orientation of the runway and that the runway is operational. At Gatwick this lighting ends at either end of the runway strip and starts in nearby fields and car parks leading to the airport. Runway surface lighting clearly defines the runway shape and length, marking the point at which an aircraft should touch down. It marks the edges and centre of the runway for a pilot to navigate an aircraft within and also marks the end points of the runway and marks the turn off points onto adjacent taxiways.

Taxiway lighting at Gatwick Airport consists of three basic components: Green centre line lighting that are located in the centre of the taxiway; Red stop bar lighting that are mounted on the ground horizontally and used to indicate to a pilot that they cannot progress any further, and blue edge lights, which are used to mark the edges of the taxiway and are there to warn pilots not to stray over them as obstacles or soft verges may exist beyond.

Aircraft movements on the ground obviously need to be tightly controlled by the control tower. The taxiway lighting system is controlled by a complex system which allows an air traffic controller to switch only the green lights that are needed for the route onto the runway and to guard against any wrong turns by switching on the red stop bar lights. The system is also intelligence driven – for example if a controller was to route two aircraft through the same taxiway area, the system will only allow one route through- blocking the other with red bars, effectively warning one of the aircraft not to cross in front of the other.

The AGL system is built on Programmable Logic Controllers (PLCs), which scan the switches and keys located in the Tower and turns these key presses into commands that are distributed across several substations located around the airport. Each substation contains PLCs that interpret the commands, check them with built in safety logic to confirm the actions that are allowed and switch on or off the lighting that is currently required. Once this switch has taken place, the substation PLCs will report back to the tower to confirm the status of the lighting, which will then show up on the tower’s control panel to confirm exactly what has occurred.

The heavy power element of the lighting is supplied by constant current regulators, which provide an accurate and adjustable current output. This means they can be controlled to provide various output levels (brilliancy levels), allowing the lighting to be adjusted to suit the prevailing weather conditions.

In good clear conditions the lighting needs to be set to dim, to avoid dazzling a pilot. In contrast, in poor visibility the lighting needs to be bright to be clearly seen. An air traffic controller makes this selection by measuring the ‘runway visual range ‘(how far you would be able to see on the ground if you stood on the runway) and the cloud base (how far you could see if you looked up).

The light fittings themselves are mainly conventional halogen lamps. However, BAA Gatwick are investigating the use of Light Emitting Diodes (LED’s) which use around 25% less energy. Gatwick has also introduced controlled beams on light fittings, to reduce upward light pollution. The airport works in partnership with its local community and has in place a sustainable development strategy which outlines a range of commitments to manage any negative impacts of its operation. Gatwick is committed to minimising the impact of light pollution and takes its responsibility to environmental management very seriously.

Maintenance

Due to the safety critical nature of the airfield lighting system at Gatwick, there is a rigorous and intelligent system of maintenance in place. A team of 27 engineering technicians are responsible for:

• 250 approach lights – white
• 600 runway lights – white
• 4,000 taxiway centreline lights – green
• 400 taxiway edge lights – blue

Throughout a 24 hour shift period, a team of five shift technicians are on call on any one time. Supporting the engineers, Gatwick’s airfield operations team operate daily checks on the lights at ground level, dividing the airfield into 28 checking areas.

As well as day to day on the ground testing and checks by the airfield operations team and engineering technicians, the system is also tested twice yearly by Flight Precision, a company that carries out a range of flight lighting checks by its aircraft and also the air calibration of the airport’s instrument landing system. All aircraft are equipped with flight inspection systems to provide comprehensive checking and calibration of radio and radar navigation aids.

The future

Gatwick has developed a simple, yet effective fault texting system, that alerts engineering technicians to any faults on the system immediately. Previously faults were sent to a computer in the engineering technicians’ office. The new paging system alerts an engineer to the exact location and nature of the fault. The system has improved productivity and reliability.

Gatwick is also in the process of upgrading the approach and runway lighting software. The Airfield Ground Lighting system at Gatwick is currently managed by two separate control systems. A new £2.1 million project is currently underway to integrate the software, ensuring a fast, reliable, accurate and user friendly system. The new software is being installed in all substations, with a ‘go-live’ date of June 2005.