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Thread: Planning approaches, and early warnings vs environmental snags

  1. #1

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    Planning approaches, and early warnings vs environmental snags

    Murphy's law claims that if something can go wrong it eventually will, if men can plan something,whether a warning system or a instrument approach or things that look good on the surface, there is inevitably a weak point, something that in retrospect may seem simple or obvious.
    The flaw in this latest warning system is said to be just computer operator error, selecting the wrong input. But in the past there have been other similar cases where the glitch was an overlooked environmental factor. Some had no harm done, but one approach error was critical.
    I don't have the exact info on the first case, but it was when a type of early warning radar or something similar was set up in Alaska in order to detect Russian long range bombers which might be heading over the more direct North pole route to attack the U S. This Defense Early Warning system would have been in the post ww II days decades ago. All went well till an alert was triggered at NORAD in the middle of the night and and there may have even been intercept fighters launched. Fortunately, there was some backup check and it was quickly determined that this was a false alarm. What triggered it? The moon, hard as it may be to believe. The planners of the system had not taken into acount the effect of a full moon rising which set offf the radar or whatever powered the system.

    Another error from an environmental or fact of nature was not so lucky in outcome. The airport at Eagle has an adequate runway length and width for corporate jets and airliners , but it is located in a valley with higher terrain within 5 miles on all sides. The highway runs along the river and railroad just to the north on the valley floor. Many years ago, and early version of an instrument approach was installed during the summer and seemed to work fine. It was not an iLS, I seem to recall that it was an ADF (NDB) approach. Anyway one day in imc conditions there was a fatal accident on the approach. I read the accident report at that time, seems to me it was Learjet and may have been at night in December. When the NTSB investigated they found that the critical difference between when the approach had first been installed and tested as working well in the summer and they had not taken into account the effect of having snow on ground as was the case when this accident occurred. Seems hard to believe that this could change a signal but that was the finding. I never heard of this anywhere else, but the FAA first prohibited that approach and finally removed it. I'm not sure if a vor approach came next, but I know there was not radar for a long time and now there is radar on iLS type guidance.in thinking back on this , I wonder if it could have been a Loran approach back then, I just cant recall for sure, just that snow on the ground affected the signal. This was long before gps.
    Last edited by Bill Greenwood; 01-17-2018 at 05:33 PM.

  2. #2
    lnuss's Avatar
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    Snow (and many other things) can, indeed, reflect radio signals. I have a very vague recollection of what you're talking about, but don't remember the approach type.

    Larry N.

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    rwanttaja's Avatar
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    Quote Originally Posted by Bill Greenwood View Post
    I don't have the exact info on the first case, but it was when a type of early warning radar or something similar was set up in Alaska in order to detect Russian long range bombers which might be heading over the more direct North pole route to attack the U S. This Defense Early Warning system would have been in the post ww II days decades ago. All went well till an alert was triggered at NORAD in the middle of the night and and there may have even been intercept fighters launched. Fortunately, there was some backup check and it was quickly determined that this was a false alarm. What triggered it? The moon, hard as it may be to believe. The planners of the system had not taken into acount the effect of a full moon rising which set offf the radar or whatever powered the system.
    Yes, this is pretty famous case.

    I was involved in a similar one, only more hi-tech and kept out of the press. In the Air Force, I was an on-duty engineer monitoring the operation of a series of satellites that detected missile launches from the infrared energy (heat).

    Of course, missiles weren't the only things that generated heat. One night we got slammed with a bunch of data on the very horizon of the Earth that mimicked the motion of a missile. Fortunately, the operators saw the data start to appear, and put the system into the manual mode.

    Now, it was well known that the system would react to celestial IR sources, and automated processes ensured these didn't affect the system. In this case, though, one star bright in the IR spectrum actually refracted through the atmosphere and the data started appearing in places it wasn't expected.

    Even that shouldn't have caused an issue, but: The programmers had the wrong value of Pi in the system. Never did hear the magnitude of the error...but it was enough to cause the data to be computed as coming from the surface of the Earth, rather than above the horizon.

    Ron Wanttaja

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