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Going frangible: all airports are required to replace approach lighting masts by 2005, but Heathrow is ahead of the game.

The replacement of airfield tights and runway approach lighting masts is an ongoing process for airside operation teams, but in 1995 ICAO issued frangibility (flexibility) standards for approach masting. Since then, airports have been forced to look at how they can best meet the 'new' requirements. The aim of the new ICAO standard was to minimise any threat these 'obstacles' could present to an aircraft in the event of the two coming together. The mast must be designed to break up upon substantial impact, so that it can not damage an aircraft's structure. The problem had been highlighted in 1971 when a Pan Am 747 taking-off at San Francisco Airport struck approach lighting--two of its main landing gear wheels were lost and parts of the lighting mast pierced the aircraft's skin.

It should be mentioned that ICAO's requirement does not apply solely to the mast, light and cable wiring, it also covers other items around the runway and flight path, such as ILS antenna and signage. Consequently, manufacturers have had to incorporate the new frangible standard into their designs.

Because it runs a number of international airports, BAA has been involved with an ICAO working group (along with representatives from six other countries) on frangibility for some considerable time. Initially this focused on defining as a minimum requirement the force and absorbed energy occurring from an impact on a support structure if hit by the wing of a 6,600lb (3,000kg) aircraft at a speed of 87mph (140km/h). Subsequently, simulated impact trials have been concluded and following on from these, the working group is now looking into the possibility of using computer simulation for any future trials of this sort.

With ICAO having issued the new directive and the UK CAA having incorporated it into its aerodrome licensing requirement, London Heathrow Airport took the lead within BAA and became the first to implement the ruling, as Heathrow's Head of Airside Operations, Ian Taylor explains: "The mast manufacturers had first to meet the ICAO stipulated rules, so it was really a case of buying an off-the-shelf product. We have a database of manufacturers from which to purchase any such equipment items and so discussions were opened with a number of potential known suppliers to meet our requirement, although any company was invited to tender.

"As you can imagine, we have some very large capital spend items at this international airport, such as baggage systems, and this normally entails a framework supplier agreement being set up. However, in this case, because of the relatively small cost of the purchase, this was not required of the companies tendering. Needless to say we, as the purchaser, had our own criteria to be met in buying the equipment and this took into account a range of issues, not just price. Out of this process we chose the Finnish manufacturer Exel for our new runway masts.

"Regarding the integration of the new masts within our airside schedule, this has been fitted around existing and routine maintenance work, in this case lighting replacement, as this is much more efficient and makes for an easier project overall. The new masts were assembled beside the existing masts and then lowered into place. This work has been phased over a considerable period of time, the first installations having taken place in the late 1990's. Obviously, we tried where possible to avoid the wintertime with its shorter daylight hours and generally poorer weather, but it has been possible to carry out the work both during the day and at night.

"We have two CAT III runways, plus a cross runway here at Heathrow and at this stage, five out of the six approaches have been fitted out and the final one is being done later this year. As for maintaining the masts themselves, it is BAA policy that any item that has a safety implication is maintained by or through us."

BAA has considered the needs of its airports on an individual basis, rather than make a company-wide purchase. "We are all different types and sizes of airports and in any case, because of ongoing works the time schedule was not the same at each. Therefore it was sensible for each airport to purchase the items separately, as and when they saw fit. The total purchase for replacing Heathrow's masts was small, in the region 1 million [pounds sterling] ($1.8 million). The other reason why this purchase was looked at on an airport-by-airport basis was because technology moves on. Over time, the supplier or product can change, therefore what is best now, may not be the case in a couple of years time when equipment is refined or improved upon. On this occasion we purchased the masts from Exel, and the lighting from UK company Ernie but this need not necessarily be the case next time."

ICAO Recommendations & Requirements

ICAO defines a frangible object as one of low mass designed to break, distort or yield on impact so as to present the minimum hazard to aircraft.

In categorising obstacles, ICAO says that all fixed objects, or parts thereof, that are located on an area intended for the surface movement of aircraft or that extend above a surface intended to protect an aircraft in flight, are by definition 'obstacles'. It states that "The first objective should be to site obstacles so that they are not obstacles. Nevertheless certain airport equipment, because of its function, must inevitably be located so that it is an obstacle. All such equipment and associated supports shall be of minimum mass and designed to be frangible in order to assure that impact will not cause the aircraft to lose control. These may include elevated runway taxiway and stopway lights, approach lighting systems, visual approach slope indicator systems, signs and markers, wind direction indicators, ILS equipment, MLS equipment, radar reflectors, anemometers, ceilometers, transmissometers and security fencing."

Thanks go to Sam Birmingham at the BAA Press Office for her help in the preparation of this feature.
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Title Annotation:Airfield Lighting
Comment:Going frangible: all airports are required to replace approach lighting masts by 2005, but Heathrow is ahead of the game.(Airfield Lighting)
Author:Penney, Chris
Publication:Airports International
Geographic Code:4EUUK
Date:Jan 1, 2004
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