I would like to welcome everybody to the new Airfield Engineering Forum which has been launched due to feedback from Airfield Engineering staff throughout UK. We have been working for several years on promoting competency and safety for staff working on airfield ground lighting (AGL) but would welcome debate on any airfield engineering topics.

An interesting subject at the moment is the adoption of LED fittings on taxiways to replace traditional tungsten halogen fittings. Feedback generally seems to be positive but any practical experiences would be useful.

Great to see Airfield Lighting being recognised, as I have been working on AGL for many years and to get people to appreciate what we all do in the cold and the wet is difficult, to them it's only a light ,not a terminal
Hopefully through this forum we will now as a group, be in a position to lift the profile of airfield lighting to the position it deserves
And hopefully we will be able to encourage companies to invest in there staff, so as to ensure high standards of workmanship and safety

With regards to LED Lighting
I work for a Large Airport with approx 18000 fittings in the ground, and as you can imagine the cost to maintain the fittings is quite considerable, hence some years ago we looked to install LED fittings, and to date we now have around 7000, as a result of the very high MTBF of the LED Light fittings, we have had a large reduction of fittings being returned to our lighting workshop, which has resulted in the Lighting workshop being able to carryout other work.
So for us now, we would only look to install LED fittings and other LED products on the Airfield

But I believe LED fittings are only the start, as currently the fittings are designed to work on existing infrastructure
I believe the AGL fraternity also now needs to look at what's under the ground and in our substations, with regard to how we feed the fittings ie AC or DC

As there are lots of Airports that have ageing infrastructure, that in the near future will need to be replaced
I would welcome anyone's thoughts on these topics

I'm staggered! Each to their own, I suppose. I tried to get the IET interested in reliability engineering without any success.

Just out of curiosity, how do calculate your MTBF?

We have an ever increasing number of LED fittings at our airport and it would seem for a number of reasons we are meking them comply with existing infrastructures. I agree that we need to look at new systems that will power the LED as they were designed to be powered.

I would be interested in comments on the following:

Since LED fittings and new technology circuits will reduce the power required could we then consider alternative standby power for use during LVP than the present diesel driven generators?

Do we need to agree a colour band for LED fittings?

I work for a well renowned AGL manufacturer, we normally calculate and evaluate MTBFof LED inset taxiway lights in accordance with MIL Standardization Hanbbook MIL-HDBK-217, "Reliability Prediction of Electronic Components".
The relevant chapter is: 2.2 Discrete Semiconductors.

A colour band for the LED's is only important if a specific airport were to mix different manufacturers. At present the specified colour spectrum from ICAO and CAP does allow too much variation, however the variation only matters as mentioned above when LED's from different manufacturers are mixed on a specific service or visual queue.

However our company has used the common colours of traffic light signals which the human eye is already accustomed to and can easily differentiate.

You'll probably be aware that MIL-STD-217 is about the same as looking into a crystal in the hope of seeing what the mtbf is. It is significantly flawed. It assumes exponential failure rate and the fact that the pi factors bear no resemblence to reality makes a 217 prediction inane. 217 doesn't provide any calculation of confidence intervals either, which makes the 'calculation' fairly meaningless.

Furthermore, mtbf infers that the item is repairable, when in fact it isn't, e.g. LEDs and other electronic components. What you are 'calculating with 217 is mttf, (mean time to fail), which is very different.

Reliability analysis of repairable items is a bit more complicated, involving maximum likelihood parameter estimation and non-homogeneous poisson process.

For newcomers to the Airfield Engineering Forum remember what you see when logging on is only the Welcome to the Airfield Engineering Forum. To see new discussions/topics remember to click on "Latest Topics" to see new posts.

I'm glad there's an airfield lighting section now (I've only just found it). It's a chance for us airfield guys to get recognition for what we do.

For years I've heard enough from people who say 'glorified light bulb changer', yet suggest they attend a controls fault in the 'A' centre of 'B' centre and they haven't a clue.

It's great stuff with an array of controls, miles of cables, transformers, regulators all to keep us busy!

I'm staggered that there is a forum for this. Judging by the posts since May 2011, I don't think there's much going on in the world of airfield lighting.

How did this topic come about? It isn't your normal field of engineering!

Hi Diesel1,

For all its worth, I fly light aircraft and I think the use of LED lighting can be a much better alternative because light intensity seems to be softer. I think it's still important to investigate the best possible uses of it and how it can save electricity with the aging infrastructure.

Using the PAL (Pilot Activated Lighting) Keeps it simple in some of the smaller metro airfields but the benefit of LED is you can have the ability to pinpoint the light direction better which is important for VASIS (Vertical Approach Slope Indicator System) Which also means colour spectrum will change according to angle and height for aircraft on approach. This info may not be directly helpful to your original question, but somewhat interesting...

Plenty going on in the world of Airfield lighting, but in the grand scheme of things, Airfield lighting is a smaller sector than other electrical areas, of which you'll only find in one place.

Add to that, in the way of forums, there are more people talking about something pretty much everyone does, but AGL isn't one of those trades in which everyone does or has a go at doing.

The reason I ask is that I've been trying to get the IET interested in reliability, which really coming to the fore. But, apparently they deem airfield engineering to be more important than reliability. It doesn't surprise me.

The original development of LED fittings was mainly around a retrofittable unit that could simply replace a lamp fitting as this was the easiest and least expensive way of introducing LED's for airfield use. This necessitated including transforming and regulating electronics inside the fitting to convert the 6.6 A Constant Current supply to a power supply that the LED's are comfortable with. ADB has developed two solutions for electrical infrastructure to provide LED fittings with the most technically suitable power supply. One is the APS system that utilises the same series circuit that is installed but replaces the CCR and doesnt require a series isolation transformer. The other is a parallel system that requires new cables and a parallel circuit voltage supply unit. Paris CDG has used the parallel supply for all their stopbars for the last 4 years.The APS system is in use in the UK and all around the World. Both these solutions provide a substantial power reduction and simpler fittings.