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Safety Action

Summary

Australian Transport Safety Bureau (ATSB) Action

As a result of this occurrence, the ATSB (formerly BASI) issued Safety Advisory Notice SAN19990083 concerning un-notified back beam radiation from a localiser. The safety deficiency noted that back beam radiation from a localiser may give false course indications if the navigation aid frequency is inadvertently selected for an approach.

There are no published procedures for the conduct of a precision approach using course guidance from a LLZ back beam. However, it is possible for an aircraft intercepting the back beam of the LLZ for runway 33 at Cairns (identifier ICN, frequency 109.5 MHz) when making a LLZ approach to runway 15 at Cairns (identifier ICS, frequency 109.9 MHz), if the incorrect approach aid frequency is manually selected. Other locations within Australia where similar localiser configurations exist may cause similar problems. Crews of advanced technology aircraft must exercise extreme caution in tuning and identifying navigation aids to ensure that the correct navigation aid frequency has been selected. Depending on the configuration of the selected navigation display mode, there may be insufficient cues displayed which would alert the crew that an incorrect navigation aid has been manually selected. Additionally, crews must ensure that Flight Management Systems are correctly programmed, and that a high level of situation awareness is exercised during the approach phase.

SAFETY ADVISORY NOTICE SAN 19990083

Operators, Airservices Australia, and the Civil Aviation Safety Authority should note the safety deficiency identified in this document and take appropriate action.

Local Safety Action by the operator

As a result of this occurrence the operator advised it had issued a notice to its flight crews that contained the following information:

"Caution during CS 15 ILS/LLZ DME Approach

A recent incident during a 15 ILS approach to Cairns revealed that if the R33 (sic) LLZ frequency is inadvertently selected in lieu of the 15 ILS frequency, the 33 LLZ is capable of transmitting a back beam that the aircraft may capture. Crews must exercise extreme caution tuning and identifying navigational aids to ensure the correct frequency has been selected. Depending on the configuration of the selected navigation display mode, there may be insufficient cues displayed which would alert the crew that an incorrect navigation aid has been manually selected. Additionally crews must ensure that flight management systems are correctly programmed and that a high level of situational awareness is exercised during the approach phase."

 
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