Capt T A Davies is correct ("No mystery about ILS signals", Flight International, 1-7 April): there is no mystery about instrument landing system signals. However, this seems to be generally known by design engineers. It does not appear to be common knowledge with pilots or maintenance engineers.
The International Civil Aviation Organisation has written to all contracting states advising them about the possibility of erroneous signals being transmitted. These signals can be the result of maintenance error, but are more likely to caused by normal maintenance procedures, where a special signal is transmitted and used in fine tuning the ILS. Erroneous signals can also be encountered on the localiser.
Air New Zealand has produced a training video, A free lesson: Flight NZ 60, which Flight Safety Foundation has incorporated into its Approach and Landing Accident Reduction programme. The video has been developed with the support of Airbus, Boeing, Air New Zealand and the New Zealand Civil Aviation Authority, which has a copy of the NZ 60 report (www.caa.govt.nz) available under "Accidents and Incidents".
The report looks at the event from the airborne, ground maintenance and regulatory aspects, with recommendations for all parties involved, including ICAO.
Michael Carrelli Safety Investigator, CAA of New Zealand
Source: Flight International
