Let There Be LEDs

Martyn Cartledge explains how Manchester Airport is leading the        way with recently approved LED lighting technology.

On August 17, 2012, a NOTAM was issued by the UK’s CAA approving the use of high-intensity LED (light-emitting diode) inset lighting. It has opened the door for many UK airports to introduce these lights for both runway centreline and touchdown zone lighting. (All images via author)

On August 17, 2012, a NOTAM was issued by the UK CAA approving the use of high-intensity LED (light-emitting diode) inset lighting.  It has opened the door for many UK airports to introduce LEDs for both runway centreline and touchdown zone lighting.  However, there is quite a story behind this decision.
Manchester Airport (MAN), UK, has been one of the driving forces in getting high-intensity LEDs approved for use by the UK regulator.  Back in 2008, owner and operator Manchester Airports Group (MAG) decided that the existing approach and runway lighting system on the airport’s principal runway (05L/23R) – which was more than 20 years old and reaching the end of its design life – required complete replacement to ensure continued safe and efficient operation.  The contract to refurbish the runway was awarded to construction group Costain, with atg airports as the successful electrical contractor to install above ground level (AGL) constant current regulators (CCRs), approach masts, and new AGL circuits, among others.
A major programme of works was required to refurbish and renew the original 05L/23R runway.  MAG decided that simple replacement of the lights was not enough and the engineering department was tasked with finding innovations and systems to reduce both the electrical energy and the carbon footprint of the airport.

The contract to refurbish the runway was awarded to Costain, with atg airports as the successful electrical contractor to install above ground level (AGL) constant current regulators (CCRs), approach masts, and new AGL circuits, among others.

Mike Curry, External Engineering Manager for Manchester, who headed up the trial and eventual programme of installation, spoke with Airports International to give background on the story.  Although low-intensity light units for taxiways and runways have been quickly adopted by the industry following a short trial at London Heathrow, high-intensity LEDs were not available at the time.
A series of NOTALs were issued for the Civil Aviation Authority (CAA) to maintain control over the equipment critical to runway safety.  The last one, 5/2006, effectively ring fenced high-white lights until the industry could demonstrate compliant fittings.
Such a product became available in late 2010 and the Aerodrome Operators Association (AOA) Technology Working Group commissioned an evaluation trial of LED runway centreline lighting.  Facilities were provided by Manchester Airport and supported by the CAA, utilising products from lighting technology company ADB Airfield Solutions.
The trial lights were supplied for no cost by ADB, which was the original supplier of MAN’s lights with its F-range (Flush) back in the late 1980s and early 1990s – when it was a new concept for the industry.  Introduction of the F-range units into the new 23L/05R, led to a considerable amount of experience and trust being built up between the two companies.  So despite MAN being the first major UK airport that ADB had fitted with LED lighting they were chosen as a preferred supplier but with the process going out to competitive tender.
Regardt Willer, ADB’s Regional Manager for Northern Europe, explained to Airports International the engineering principles and challenges created by such an installation.  Unusually, Manchester’s runway and taxiway systems run at 12 amps, rather than the routine industry norm of 6.6 amps.  It means that all of the fittings were constructed at 6.6 amps and an isolating transformer was sourced to step down from the 12 amps, against the normal 1:1 ratio.  The cost for the units, which are available from only one supplier, is rather high in relation to standard versions available from a number of other sources.
The trial lights were pre-production units, which became standard by the time they were required for the full length of 23R/05L.
The trial LEDs, installed on February 16, 2011, lasted up to the end of that year, employing pre-production units on the first 3,281ft (1,000m) of the runway with existing fittings.  This particular runway was chosen as it is presently CAT 1 only.  It yielded valuable information that pointed towards compliance being attainable with the next iteration of the light units.
A second phase on runway 05L/23R began at the end of 2011 using final production light units supplied by ADB.  The trial had now expanded – in addition, the centreline of runway 05L/23R and touchdown zone lighting were changed to LEDs, with similar checks, measurements and inspections repeated as happened in the first phase.
Information was drawn from a number of sources and a considerable amount of testing and readings were taken.  The CAA undertook a series of test flights, the first of which occurred on the day of installation.  In addition, operational aircrew provided ‘real-time’ feedback, which demonstrated a high degree of acceptance, with both sets of LED light units underlining the progress made in harmonising the brightness with halogen lamps at lower settings.
Previous trials in the US had not been as positive and feedback from there came at just the right time for the MAN trial.  In the US trials (in particular at Raleigh Durham), despite set tolerances and actual brightness, it became clear that the human eye perceived the lights as brighter than they really were.  To solve the problem, ADB created what was described as a human perception-dimming curve.
Mike Curry and his team linked up with Manchester University to study the issue further.  The university conducted tests in its cloud chamber to see how different lights penetrated in low visibility conditions, using standard metering equipment and the human eye.  This ongoing work could set new standards and even change regulations in the future as there are massive possibilities for enhanced capabilities when low-visibility procedures (LVPs) are used at airports.
At this time, FedEx had developed an ‘enhanced vision system’ to assist delivering crews to remote airports.  But the system did not ‘see’ the LEDs, and modifications took time to develop.  However, FedEx was not keen on releasing its self-developed specification, making it difficult to alter LEDs in this way.
Results drawn from both phases demonstrated that high-inset red and white LED units could be installed in an operational environment and meet compliance satisfactorily.  The AOA Technology Working Group submitted its report with supporting evidence and a draft Information Notice to replace NOTAL 5/2006, requesting a change of policy.
The submission satisfied the Aerospace and Defence Industries Association of Europe (ASD) that the inset LED light units were compliant with the requirements set out in CAP 168, Chapter 6, and demonstrated an equivalent level of safety and dependable serviceability to that provided by similar incandescent sourced light units.  There were no unintended consequences from the trial, nor any failure modes that would have highlighted unsafe conditions.
LEDs and halogen compared
LEDs use less power and have lower maintenance levels than halogen lights, lowering bottom line costs.  Halogen lamps tend to grow more yellow with lower intensity while LEDs remain the same colour.  As halogen lamps degrade there is further colour change, which does not happen with LEDs.
MAN is now looking to replace the runway edge lights and any new lights are expected to show a return on investment within one or two years.
Approach lights were also replaced during the major refurbishment of 23R/05L, but CAA regulations state that halogen and LED cannot be mixed in the same service so the diodes could not be used.  Due to the re-profiling of the approach and alignment of 23R, the new
lights were also placed on new masts and poles along with complete rewiring.
Elevated LEDs are currently available but the technology
to produce them as inset approach lights does not yet exist because the small aperture in the fittings prevents the required 20,000 candelas being produced.  Therefore, as MAN – along with 90% of the UK – has such a requirement due to its displaced runway threshold, a solution is awaited.
Halogen technology has also been evolving and a 200W unit, which might have been previously required, is more likely to take a 150W unit, saving 25% on power.
The coming year will see ADB focus on runway lighting, utilising the latest generation of products that incorporate low harmonic regulators using pure sine wave at the to create further savings.  The state-of-the-art units use 30% less power and last longer as the LED forms a better fitting within the structure.  LEDs have taken MAN along the road to success – a journey that is likely to continue.