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Topic Title: Monitoring of LED AGL Fittings
Topic Summary: Is the monitoring of LED AGL fittings necessary
Created On: 18 July 2011 02:01 PM
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 18 July 2011 02:01 PM
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iraadb

Posts: 5
Joined: 09 December 2010

Attached are my thoughts on the monitoring of LED AGL fittings. I would appreciate other members comments/thoughts on this subject.
The monitoring of AGL fittings to detect lamp failure was introduced for a number of reasons, maintenance requirements, etc, but primarily, to warn of adjacent lamp failure which may affect the service pattern of an AGL circuit with the possibility of showing an incorrect visual signal to a pilot.
Originally, defective lamps were detected via Lamp Failure Detection (LFD) incorporated in the Constant Current Regulator (CCR). These monitoring circuits were not always particularly accurate; they required setting up and calibrating when the series circuit was commissioned. This was not always done. Also, interleaved circuits posed the problem that lamp failure on one service, Runway Centreline for instance, would not, necessarily, indicate if there were more than one lamp out in the service and you could not monitor the actual location of the failed lamp(s)
With the advent of Individual Lamp Control & Monitoring Systems (ILCMS) it was now possible to monitor each fitting for lamp failure and its position in the circuit, thereby being able to detect if there was adjacent lamp failure affecting the service pattern.
Most Regulatory Authorities around the World stipulate that certain AGL services should be/must be monitored for Service Pattern interruption due to adjacent lamp failure. Traditional Tungsten Halogen lamps are not consistent in quality and are not necessarily the most reliable of components usually having only a performance life of around 1000-1500 hrs, so with the introduction and implementation of LED light sources in AGL fittings with its inherent reliability and reported life of approx 56000 hrs the performance capability of LED taxiway fittings were greatly enhanced.
However, some regulatory authorities are still insisting on monitoring these fittings.
Let's look again at the original reason for monitoring the lamps:
- Detection of adjacent lamp failure to ensure integrity of service pattern
- Inconsistent quality of TH lamps giving questionable performance affecting the correct performance of the visual signal.

However, it is not just the lamp that can affect the performance of a fitting, partial/total short circuit of filament, dirty/cracked lens, water ingress in the fitting, broken filters, incorrect series circuit current, faulty series transformer, lamp performance below 50%, etc. can all affect the performance creating an incorrect visual signal. Lamp failure monitoring does not provide any feedback of these problems. It only monitors one reason for lack of performance, the light source, albeit the main reason and even then it can't detect short circuit of the filament.
The same parameters for compliant performance also apply to LED fittings, however, the main reason, failure of the light source, is greatly reduced due to its extended life and reliability compared to a TH lamp. The LED is one of the most reliable components in an LED fitting.
Therefore why do we need to monitor only one component that is proven to be unlikely to fail? Recent evaluations of over 6000 LED taxiway fittings installed on one airport over a period of 7 years have shown the reliability of LED fittings, 64 failures with over 50% of these due to mechanical damage, not component or LED failure, gives a calculated MTBF of over 70,000 hrs against 900 hrs for a TH fitting. Not one returned fitting had an LED failure.
Why introduce sophisticated monitoring circuits at extra cost to monitor the unlikely, only one component of potential failure, and reduce the MTBF?
One reason is the interpretation that some regulatory authorities put on the ICAO requirements.
The requirements of ICAO are that the failure of fittings, especially adjacent fittings, should not affect the service pattern creating an incorrect visual cue to a pilot. Only providing Lamp Failure Monitoring does not fully satisfy this requirement.
As we have mentioned above the failure of a light source (lamp or LED) is only one potential cause of an incorrect visual cue.
Also, dependence on LFD technology to warn of non-performing lights can lead to complacency in the maintenance of AGL services.
The best way of checking for compliant performance of AGL fittings is to conduct photometric measurement utilising a mobile photometric measurement device, however, in normal Airport operations this is impractical as access to Runways and Taxiways to conduct these measurements on a daily basis would affect Aircraft operations. However, this is recommended for regular (weekly, at large Airports) checking as part of a maintenance regime to establish that the AGL is compliant to ICAO or National Civil Aviation regulatory requirements for photometric performance.
Most Airports conduct visual checks twice a day to comply with International or National requirements and this is the most practical way of detecting non-performing AGL fittings. This procedure provides a visual check on the AGL fittings between Photometric Measurement checks.
Let's summarise the issue:
- There is a regulatory requirement to avoid non-performance of AGL Fittings that could affect a service pattern of an AGL circuit. (especially adjacent lamp failure)
- There are a number of reasons that could create the non-performance of an AGL fitting. (Partial/Total short circuit of the filament, Lamp failure, dirty/damaged lens, water ingress, faulty series transformer, incorrect current input, lamp performance below 50%, etc)
- Lamp Failure Monitoring only provides feedback of one of these reasons.
- Lamp Failure Monitoring technology incorporated in the CCR or AGL fitting creates more complexity in the series circuit infrastructure thus reducing the effective MTBF of the circuit.
- LED's have proven to be extremely reliable in the application of light sources for AGL fittings. (>250,000hrs)
- Daily visual inspections are carried out by the majority of Airports.

Therefore, should we review the value of Lamp Failure Monitoring when applied to LED fittings? Has the implementation of LED fittings removed the need for Lamp Failure Monitoring?
The installation of LED fittings has already been proven to greatly reduce the requirements for maintenance and service improving the availability of taxiway systems. This has greatly reduced maintenance costs. Energy costs have also been reduced.
Costs can be further reduced by removing the cost of Lamp Failure Monitoring of LED fittings without compromising safety.
This would also improve the integrity of the series circuit by increasing the MTBF.
 26 July 2011 01:30 PM
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SGMartin

Posts: 5
Joined: 01 November 2004

A very interesting topic and one worthy of some further debate I am sure. A good case is made for the removal of the current complexity, caused by the Lamp Failure Monitoring requirements, being judged against the lack of recorded failures of LED lamps. However, is there enough data available to support this? Is one airport even with 6000 fittings installed for a seven year period a suitable and sufficient sample.

What experiences do other Airports have and what are the implications if the Lamp Failure Monitoring requirements were modified?

Is there anybody on the AOA Technical Committee, involved with LED fitting trials, who could provide some additional input?

 30 June 2012 09:49 PM
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stableford

Posts: 64
Joined: 04 April 2006

Dear all, I'm fairly new to the airfield lighting industry, but have been asked by my company to assist in inspection, commissioning a new 4km runway, in Calgary. Its currently building a new international terminal, new runway, and 3 tunnels.
One of the problems they currently have is the monitoring of led fixtures, which they would like to use, but considering the size of the airport, forgive the lack of correct airfield lingo, perhaps the rating of the airport is better terminology. They are a little bit lary regarding lamp failure monitoring gear. Do any of you have experience with led monitoring ccts or monitors that have been suitably accurate. The new controls package going in is by ADB.

Thanks in advance

Derrick
 30 June 2012 09:49 PM
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stableford

Posts: 64
Joined: 04 April 2006

Dear all, I'm fairly new to the airfield lighting industry, but have been asked by my company to assist in inspection, commissioning a new 4km runway, in Calgary. Its currently building a new international terminal, new runway, and 3 tunnels.
One of the problems they currently have is the monitoring of led fixtures, which they would like to use, but considering the size of the airport, forgive the lack of correct airfield lingo, perhaps the rating of the airport is better terminology. They are a little bit lary regarding lamp failure monitoring gear. Do any of you have experience with led monitoring ccts or monitors that have been suitably accurate. The new controls package going in is by ADB.

Thanks in advance

Derrick
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