The safety of structures located on the airfield strip was called into question in 1971. This was following a serious incident during the takeoff of Pan Am flight 845 on 30th July 1971. The aircraft struck the approach lighting systems due to a last-minute change in runway. This lead to misinformation about the takeoff length from the displaced threshold. Thankfully there were no fatalities during the incident. But, 29 passengers sustained injuries and there was serious damage to the aircraft.
The FAA conducted frangibility investigations between 1976 and 1979. The aim was to develop international regulation for the frangibility of equipment or installations at airports. Anything required for air navigation purposes (approach lighting towers, meteorological equipment, radio navigational aids) and their support structures.
Data from the Airline Pilots Association Survey 1959-1986 showed that of the 1002 incidents 41% were overruns, 33% veer-offs and 22% undershoots meaning these structures needed to be frangible. A frangible object was defined as “an object of low mass, designed to break, distort or yield on impact, so as to present the minimum hazard to aircraft”. This characteristic is seemingly contradictory to the operational requirements for stiffness and rigidity imposed on this type of equipment.
In 1981 the ICAO established the Frangible Aids Study Group with the aim of defining design requirements, design guidelines and test procedures. This work has resulted in part 6 of the Aerodrome Design Manual, dedicated to frangibility. Its 7 chapters cover:
These requirements from the FAA and ICAO are still in place today.
All Pollite masts are FAA and ICAO approved. You can find out more here.