Regulations & Technical Information
In 2006, the frangibility and deflection/wind speed requirements of approach lighting masts and other obstacles were more clearly defined with the publication of the ICAO’s Aerodrome Design Manual, Part 6 Frangibility. A manual designed to be read in conjunction with Annex 14 but offering clearer guidance on the design, testing and installation of frangible structures at airports. Frangible objects, as defined within the manual were to be of a low mass and designed to break, distort or yield on impact presenting a minimum hazard to an aircraft.
Annex 14 Vol 1 Chapter 9 specifies in detail the equipment and installations of operational significance on the airfield which should be frangible; including:
- Any visual or non visual aid located near runways, taxiways and aprons.
- Any obstacle located on an area intended for the surface movement of aircraft or that extend above a surface intended to protect an aircraft in flight.
- Any structure that presents a hazard to aircraft in the event of accidental impact during landing, take off or ground manoeuvring. Including:
- Elevated runway, taxiway and stopway lights
- Approach lighting systems
- Visual Approach Slope Indicator
- Wind Direction Indicators
- ILS equipment
- MLS Approach equipment
- Radar reflectors
- Forward Scatter Meters
ICAO’s Aerodrome Design Manual, Part 6 Frangibility looks more closely at the design, siting and testing requirements for operational equipment that is required to be frangible.
“The frangibility of any aid should always be proven before the aid is considered for installation”
The manual sets out a general expectation for testing of frangible masts including procedures and acceptance or rejection criteria.
- The structure should Break/Distort/Yield when subjected to the sudden collision forces of a 3000kg airbourne aircraft travelling at 140km/h or on ground at 50km/h.
- The structure on impact should not become entangled with the aircraft affecting its manoeuvrability.
- The structure should not impose a force on the aircraft in excess of 45kN
- Maximum energy imparted as a result of the collision should not exceed 55kJ
- Design of the mast should take into consideration individual components should be lowest mass possible
- Full consideration should be given to cabling and its segmentation.
Testing for Frangibility
“High Speed, full scale testing is a proven method for verification of frangibility” – 5.1.2 Testing for Frangibility ICAO Aerodrome Design Manual Pt 6
Within this ICAO design manual is the clear guidance that frangibility in masts exceeding 1.2m must be verified through full scale dynamic testing to ensure full compliance with the above mentioned criteria. This testing is specifically recommended for:
- Approach lighting masts
- Wind Direction Indicators
FAA Advisory Circular No. 150/5345-45C Low Impact Resistant Structures
As with ICAO the FAA issued in March 2007 an advisory circular with their own specifications for frangible masts used to support approach lighting systems. With specific regard to frangibility the FAA circular follows the same frangible design goals as ICAO’s Design Manual.