LED Aeronautical Ground Lighting: Evolution or revolution?

The development of Aeronautical Ground Lighting (AGL) has generally been one of steady evolution. Since a significant period of rapid development during the early 1940s, driven by the require – ments of wartime aviation advancement, progress has been somewhat conservative with manufacturers applying established technology to the production of smaller and more efficient light units but without pushing the boundaries too much. Many refinements have been made to the light units but the basic system and circuitry have remained the same.

However, the development of Light Emitting Diodes (LED) into a reliable light source has provided an opportunity to look at the whole system from a fresh perspective. Over the past decade much trial and some error has been undertaken with LED AGL light units at airports in different parts of the world.

The USA has been particularly prominent in the development and deployment of LEDs and the Federal Aviation Administration (FAA) has been pro-active in the evaluation and acceptance of the new technology.

In the United Kingdom (UK) the introduction of LEDs has followed a measured approach with the UK Civil Aviation Authority (CAA) requiringthe use of operational trials to demon – strate the suitability of new operational procedures or technology, referred to in NOTAL 10/2006. The Airport Operators Associations (AOA) Technology Working Group has provided technical oversight of the introduction of LED Airfield Lighting. Initially, this Working Group was involved in trials evaluating the performance of taxiway and stopbar LED light units and more recently runway light units. In 2005 the UK CAA published NOTAL 6/2005 permitting the installation of LED light units for taxiways up to and including the stop bars but excluding approach, approach slope indicators and runway lighting systems.

Subsequently, several civil airports and MOD airfields have installed LED AGL light units with a number of advantages and disadvantages becoming apparent. This has provided technical challenges that have had to be understood and overcome.

However, the general impression is favourable and the industry is now ready to benefit from the ever improving LED technology and is looking to introduce LED AGL light units on to runway circuits. Hence, recently the AOA Technology Working Group has been involved in a trial to evaluate LED light units installed on a runway centreline.

Benefits of LED AGL light units

The benefits of using LED light units as replacements for incandescent lamps have been well discussed and documented.

The increased service life of the LED light units, usually quoted at a minimum of 50,000 hours by most manufacturers, is one of the most significant reasons for converting from incandescent to LED technology.

In addition, as there is no lamp filament to degrade or suffer vibration damage and no colour filters to require replacement, the frequency of maintenance on the light unit is significantly reduced. However, the ‘in-situ’ maintenance concerning the alignment, cleanli – ness of the lens and the physical retention of the light unit will remain. This will bring both a measurable financial saving due to the reduction in costs of both labour and spare parts and a reduction in the intrusive work undertaken on active pavements.

There is also a reduction in energy consumption with the adoption of LED light units. However, when installed as a direct replacement for incandescent sourced light units, this is not as great as often expected, due to the conversion process necessary to provide the ideal LED power requirements from a traditional constant current series circuit. Therefore, several manufacturers now have LED light units and power supplies that use alternative methodologies better matched to the strengths of the LEDs. These have produced more significant energy savings in keeping with the claims originally made for LED installations.

The colour produced by LEDs also appears more intense and concentrated to the human eye than the incandescent equivalent. As the light output produced is across a narrow band of the visual range, this produces a more saturated colour. This provides a noticeable contrast with traditional light units and has already led to the recommendation that LED and incandescent light units are not interspersed.

Similarly, the perceived brightness of LEDs is also usually seen as a benefit. However, there have been some reports of pilots being dazzled by LEDs due to issues with brilliancy control. Therefore, although there are several apparent benefits to the adoption of LEDs, there are still a number of challenges to overcome.

AOA Technology Working Group and operational trials

The UK CAA requires the introduction of new operational procedures and/or systems, par – ticularly those based on innovative technology, to undergo operational trials to demonstrate they are safe to implement. This ensures a full and detailed assessment of the new procedures and/or technology that can be conducted in operational situations in a controlled manner without compromising safety. The requirement for and conditions of such trials are included in NOTAL 10/2006. The NOTAL provides details of the notification process including the nature of the information to be provided to enable the prerequisite approval to be obtained from the CAA.

The Airport Operators Association (AOA) formed a Technology Working Group to share learning and develop an understanding of the potential benefits and limitations new technology might present in AGL applications. This group was instigated to manage the trial of LED taxiway centreline light units at London Heathrow and produced its first report in September 2004. More recently, the Working Group has been involved in the oversight of the trial of LED runway centreline light units at Manchester Airport.

The Working Group draws on the expertise of representatives from a broad spectrum of AGL organisations including: the CAA, MOD, AOA, airport operators, AGL manufacturers, installation and commissioning contractors, and specialist consultants. Not only does it oversee operational trials, it continues to review its guidelines for the trials, thus ensuring the introduction of innovative AGL technology is conducted in a safe, responsible and structured manner.

Manchester Airport – A case study

The AOA Technology Working Group is respon – sible for overseeing the trial of ADB’s high intensity runway centreline LED light unit at Manchester Airport and held its initial trial meeting in October 2009. The purpose of this meeting was to establish the current state of play with respect to LED technology and prepare a programme for the development of both the CAA Approval document and the Operational Trial Plan.

The Trial Plan addressed the requirements in NOTAL 10/2006 and used the standard AOA Trial format. The Plan contained; the objective of the trial namely “to demonstrate that Light Emitting Diodes (LEDs) can be used as the light source in high intensity runway lights;” a description of the equipment, the system it is installed within and its location on the airport; the risks and sensitivities, potential benefits, test schedules and results, how the data is to be evaluated and the method of presentation, communication plan (for briefing pilots and airport staff), management plan, and health and safety plan.

It was the intention of trial to install 33 new LED light units, both white and red, in a section of the runway centreline system serving RWY 05R-23L thus enabling a direct comparison with the existing incandescent sourced light units to be made. (The LED light units were to be connected into the same constant current series circuit as the existing light units.) In-situ photometric measurement of the complete runway centreline system was also to be undertaken again giving a direct comparison between the two types of light unit. Thus, ensuring the LED light units provided a comparable light output to that of the incandescent light units which was critical to the success of the trial.

During the development of the Operational Plan information was gleaned from other LED Trials, none perhaps more significant than the LED Trial at Raleigh Durham (RDH) International Airport. The flight test during night time VFR identified that the LED light units exhibited bright signals even at the lowest brilliancy setting and as a result the FAA posted a moratorium on the acquisition and installation of LED runway centre line and touchdown zone light units until the issue was resolved.

The LED light units to be used in the Manchester trial were similar to those used at RDH and further research was undertaken to ensure a similar result to that seen at RDH was averted. Further comparative visual tests were conducted on both the LED and tungstenhalogen variants of the runway centre line light units to establish a suitable brilliancy curve.

The approval and the operational trial documents were completed in January 2010, approval received from CAA on 3 February 2010 and the trial commenced at Manchester Airport on the 15 February 2011 with the obligatory flight check and in-situ photometric measure ments. To date, apart from some minor physical defects, the LED light units have performed well giving balanced visual cues and receiving positive reports from the pilots. The trial report is being prepared and is expected shortly.

The potential for the future

Is the airport world ready to embrace the opportunities provided by LED technology and move to a new generation of intelligent AGL light units, systems and circuits or will we continue to demand that all new equipment can be retrofitted in to existing systems on a ‘like-for-like’ replacement basis?

The advancement in AGL LED technology over the past decade has now evolved to the point were we can provide the pilot with a superior quality visual aid, whilst also meeting the energy efficiency desires of the airport operators. The light from LEDs has the ability to provide a more consistent output with better colour definition and greater operating life. However, there is inconsistency between the offerings from different manufacturers, which makes it difficult for airports to plan and evaluate major upgrades to their AGL systems.

Generally we still lack formal standards for the comparison of LED AGL light units and systems and are largely reliant upon the research and development strengths of the various manufacturers to produce de-facto standards.

The FAA has again taken the lead with the publication of Engineering Brief 67D covering ‘Light Sources Other Than Incandescent and Xenon for Airport and Obstruction Lighting Fixtures’.

We currently await the publication of IEC 62519 – Technical Requirements for LED Lighting systems used for AGL Systems and also the ICAO Aerodrome Design Manual – Part 5 Electrical Systems (Second Edition).

Hopefully, these documents will provide sufficient guidance and a level of standardisation to enable the airports to be able to invest in replacing their AGL infrastructure with circuits and systems designed to gain the best results with LED light units.

Those who ventured to the 2011 Inter Airport Show in Munich will have seen the vast range of LED light units on display. Some light units merely look to replace the incandescent lamp with an LED whilst others look to utilise the opportunity LED technology provides to introduce new control facilities within the light unit itself.

Whilst we might not yet have solved all the challenges inherent with the implementation of LED Airfield light units, the established and potential benefits already dictate that there is no turning back.

Acknowledgements

The author would also like to acknowledge the significant input of Mr Andy Dunn, Chair of the AOA Technology Working Group, in providing guidance and specific details regarding the AOA and the Manchester Trials.

About the author

Steve Martin BSc (Hons) MIET is Chair of the IET AGL Competency Working Group and a member of the AOA Technology Working Group. He currently works as an Electrical Engineer for EMCOR Facilities Services Ltd. Previously Steve was the Maintenance and Engineering Director for Develop Training following several years of on-site engineering experience with the Property Services Agency.