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False glideslopes -- NZ60
An interesting thread on AirDisaster.com (including video) discusses
the false glideslope indications that nearly did in an Air New Zealand flight some years ago. This is particularly interesting given that the FAA no longer seems to require an outer marker or equivalent on ILS approaches, making it much harder to check for correct glideslope indications. http://airdisaster.com/forums/showthread.php?t=83775 Here's an excerpt from an article linked in the 7th post in that thread that explains why it happened: "On the night of July 29, 2000, the glideslope sidelobe amplifier was not operating in Apia. In addition, the ILS ground equipment had been left in bypass mode following calibration maintenance. This prevented system transfer to the standby transmitter. No alarm sounded in the control tower because the cable that fed information to the tower navigation status displays had been cut during construction. As a result, the Air New Zealand flight received only the glideslope carrier wave transmission, which was interpreted by the instruments as being on glideslope, with no warning indications." |
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False glideslopes -- NZ60
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#3
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False glideslopes -- NZ60
Buck Murdock wrote:
In article .com, wrote: This is particularly interesting given that the FAA no longer seems to require an outer marker or equivalent on ILS approaches, making it much harder to check for correct glideslope indications. That's news to me -- I thought they had only done away with the *middle* marker, no? Although the FAA hasn't decommissioned existing OMs, it is no longer a required check. There are ILSes, for example, where the G/S can only be cross-checked with DME, yet DME is not required for the full ILS. The issue that occurred in Oz was the result of bad maintenance practices. The FAA claims that will never happen here ;-) LPV does not have this problem. |
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False glideslopes -- NZ60
BTW - I don't seem to see the old inner markers as much as I did 30
years ago. Haven't really even thought about it until just this thread, but are they actually decommissioning those or just not installing new ones? -----Original Message----- From: Sam Spade ] Posted At: Tuesday, January 30, 2007 9:04 AM Posted To: rec.aviation.ifr Conversation: False glideslopes -- NZ60 Subject: False glideslopes -- NZ60 .... Although the FAA hasn't decommissioned existing OMs, it is no longer a required check. There are ILSes, for example, where the G/S can only be cross-checked with DME, yet DME is not required for the full ILS. .... |
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False glideslopes -- NZ60
Jim Carter wrote:
BTW - I don't seem to see the old inner markers as much as I did 30 years ago. Haven't really even thought about it until just this thread, but are they actually decommissioning those or just not installing new ones? I believe inner markers are mandatory on CAT II approach procedures. Every CAT II in the western U.S. that I looked up has an inner marker. |
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False glideslopes -- NZ60
On Jan 30, 7:04 am, Sam Spade wrote:
Although the FAA hasn't decommissioned existing OMs, it is no longer a required check. There are ILSes, for example, where the G/S can only be cross-checked with DME, yet DME is not required for the full ILS. Well maybe not technically decommissioned, but the ILS27R at Oakland was redesigned and they stopped using the outer marker (Cases) in favor of a DME fix about 1/2 mile away. The outer marker is still there, and I believe it shows up as a grayed out fan marker on Jepp plates, but not at all on government plates. Are there others? I'd guess so. |
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False glideslopes -- NZ60
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#8
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False glideslopes -- NZ60
On Jan 31, 2:59 am, Sam Spade wrote:
In that case the P-FAF was moved to be coincident with the non-precision FAF, if I recall correctly. Why is that important? I guess its easy to do if you're using DME fixes, but why do that if you're not going to decommission the outer marker? |
#9
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False glideslopes -- NZ60
Are you speaking to outer marker or Compass Locator at the Outer Marker?
Al. wrote in message oups.com... On Jan 30, 7:04 am, Sam Spade wrote: Although the FAA hasn't decommissioned existing OMs, it is no longer a required check. There are ILSes, for example, where the G/S can only be cross-checked with DME, yet DME is not required for the full ILS. Well maybe not technically decommissioned, but the ILS27R at Oakland was redesigned and they stopped using the outer marker (Cases) in favor of a DME fix about 1/2 mile away. The outer marker is still there, and I believe it shows up as a grayed out fan marker on Jepp plates, but not at all on government plates. Are there others? I'd guess so. |
#10
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False glideslopes -- NZ60
Allan9 wrote:
Are you speaking to outer marker or Compass Locator at the Outer Marker? Al. Check the Jepp chart. It is the OM. |
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