NLR develops frangible airport tower

ILS towers form part of the radio navigation systems that allow aircraft to make precision approaches to runways. Should a collision occur, these towers must break without causing appreciable damage to the aircraft or injuring passengers.

The new frangible composite towers meet all ICAO (International Civil Aviation Organization) and FAA (Federal Aviation Administration) requirements. Following two-years of development, supervised by NLR, the ILS towers frangibility was successfully demonstrated during a series of tests.

Photo: The impact test involved a wing structure mounted on a special trailer being driven into a 16-metre high ILS tower at a speed of 140 km/h, which is the approximate landing speed of a small aircraft. The ILS tower broke at various points, as NLR had calculated in advance. The generated force and energy was measured during the tests. Five high-speed cameras, focused on different parts of the tower, recorded the impact.

Click Here to view movie of the test

NLR was involved in all phases of the project development. Supported by advanced crash simulations conducted at NLR, the towers design was optimised to meet the strict standards set for both statics and frangibility. This was achieved through the use of lightweight composite materials and the development of innovative failure mechanisms that ensure the towers experience controlled breaks during impact. NLR, moreover, served as a consultant in setting up and conducting all the experimental tests during the project. The ILS tower tests were conducted at Leipheim Airport, in Germany. Present at these tests were representatives of Europoles, and the American firm SES, as well as delegations representing the US Air Force and US government. The vehicle safety specialist from CW Concept Technologie conducted the 140km/h full-scale impact tests. In its initial stages, this project was financed by an SBIR
(Small Business Innovation Research) provided by the USAF, for which NLR was fully compensated.

In late September NLR presented the project results at the International Crashworthiness Conference ICRASH, held in Leesburg (USA). Recommendations for the ICAO and FAA are being prepared in order to include test procedures and standards relating to large frangible structures at airports in a new regulation.

Airport safety is an important aviation research field. Consequently, for many years NLR has been conducting comprehensive research in areas such as runway incursions and bird-strikes. Collisions with physical structures at airports, such as with light towers positioned along the taxing runaways or with approach light towers situated at the beginning of runways, are included in this research. These towers must adhere to strict frangibility standards.