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NZ flt 60, erroneous glideslope leads to near CFIT

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  • NZ flt 60, erroneous glideslope leads to near CFIT

    Current pilot mindset makes it very difficult the distrust the ILS, despite conflicts with other instrument readings. But the ILS is not infallible. The recent MyCargo 6491 crash was a case of 'false glideslope'. Another potential threat is 'erroneous glideslope'.

    The difference is that, with 'false glideslope', you are encountering a 'mirror' set of side lobes AFTER the actual glideslope at an angle steeper than the actual glideslope (though potentially reversed in phase), whereas with 'erroneous glideslope' you are encountering only the glideslope carrier signal, which carries both the 90HZ and 150HZ signals in balanced proportion. The carrier signal alone will always result in an 'on glideslope' indication no matter where you capture it, so you would tend to capture it from below (or immediately upon selecting APP) and begin your descent BEFORE the actual glideslope. 'Erroneous glideslope' is caused by a lack of side lobe signals, which, in this case, was due to a maintenance procedure where the back-up system was improperly left in bypass mode. That makes this an extremely rare and unlikely scenario. Still, without TAWS or EGWPS, only visual cues very near to disaster alerted this crew to go-around...

    Very interesting video recreation of the incident here: (note: abundance of acronyms may make 3WE's head explode)

    An Air New Zealand 767 encounters a malfunctioning ILS Glideslope system which forces it to go around. A saftey instructional video discusses the event and t...


    The end of the NZ60 Apia ILS incident video, showing how the steps the pilots took prevented a crash, resulting instead in nothing but a delayed flight.


    The end of the NZ60 Apia ILS incident video, showing how the steps the pilots took prevented a crash, resulting instead in nothing but a delayed flight.




  • #2
    Originally posted by Evan View Post
    ***pilot mindset***abundance of acronyms may make 3WE's head explode***
    Awesome incident, Evan.

    Insidiousness, Cowboy Airmanship, Procedure, Human Factors (like confirmation bias, AND a totally routine ILS done many times before), Cryptic autopilot modes...

    ...and the day was saved by that fundamental cross check that applies to 172s, 200s, 236As, Boeings, Airbusses, and cargo jocks.

    "We" must acknowledge that the system worked.

    Conversely, why don't 'we' just get the GPS/RNAV/FMC/Magenta line painter thingie to calculate a backup ILS based on other beacons and throw a flag if there's a conflict... maybe a fancy app for a full sized I-Pad?

    Hoping the authorities are monitoring.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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