Julesmusician From , joined Dec 1969, posts, RR: Posted (10 years 2 months 1 week 5 days 9 hours ago) and read 5780 times:
ILS protected I have taken to mean as not allowing any aircraft to get in the way of the radio signal by blocking it can someone confirm if this is true? Also how does this work - if you have a nice trail of aircraft in on finals then the ILS signal cannot be protected all the way out so can you lose signal coming in and what effect might this have on the approach?
Vzlet From United States of America, joined Mar 2004, 853 posts, RR: 0
Reply 1, posted (10 years 2 months 1 week 5 days 8 hours ago) and read 5763 times:
I'm not sure if this is the same thing you're talking about, but in the US, "ILS Critical Area" is used to designate a zone on the ground that taxiing aircraft should avoid when the ILS is in use, lest they interfere with the signal.
For an example, see the threshold of runway 10R in this diagram of Monterey Peninsula (MRY).
"That's so stupid! If they're so secret, why are they out where everyone can see them?" - my kid
TimT From United States of America, joined Jun 2001, 168 posts, RR: 0
Reply 2, posted (10 years 2 months 1 week 5 days 6 hours ago) and read 5745 times:
ILS Protected Area and ILS Critical Area would be the same. Detroit Metro has a couple of taxiways that have not only a "Runway Threshold" mark, but also an "ILS Hold". If the runway is in use then the ILS mark is used keeping the taxiing a/c back further from the runway. Even if it's not in use, I ALWAYS double check permission to cross the ILS line and also verify runway clearances. If the weather is actual ILS conditions and you cross over the hold line you may block either the glideslope or the localizer (or both) and someone does a go around. And someone else gets that dreaded message "Call the Tower" or gets met by an inspector.
Julesmusician From , joined Dec 1969, posts, RR:
Reply 3, posted (10 years 2 months 1 week 4 days 23 hours ago) and read 5678 times:
Thanks for that I was just wondering whether aircraft all lined up to land could cause problems for the aircraft behind on finals, but it appears not, sounds like it is just something for aircraft on the ground to beware of. Thanks.
Key From Netherlands, joined Feb 2005, 99 posts, RR: 0
Reply 4, posted (10 years 2 months 1 week 4 days 22 hours ago) and read 5670 times:
Yep, can confirm that. To disturb the ILS signal you have to be so close to the transmitter that you'd be on the ground. If you were flying that close you could disturb it as well, but only for a very short moment.
Keep in mind the glide slope antenna is to the side of the runway, so a landing aircraft will not obstruct it for the one behind in the final stages of flight. Likewise, the localizer is past the end of the runway, 'looking over' the one ahead that is touching down.
ILS Critical and Sensitive Areas, making up the Protection Area together, exist only on the ground. The worse the weather, the more protection is needed.
VuelingAirbus From Spain, joined Aug 2005, 113 posts, RR: 1
Reply 6, posted (10 years 2 months 1 week 4 days 18 hours ago) and read 5617 times:
Quoting Julesmusician (Reply 3): Thanks for that I was just wondering whether aircraft all lined up to land could cause problems for the aircraft behind on finals, but it appears not, sounds like it is just something for aircraft on the ground to beware of. Thanks.
You are wrong. It is a huge problem. Spacing of landing traffic is double or more in actual low visibility operations (I think I mentioned that to you in one of your previous threats already). That's the reason why the runway capacity is less than half in foggy conditions.
Bond007 From United States of America, joined Mar 2005, 5650 posts, RR: 8
Reply 8, posted (10 years 2 months 1 week 4 days 12 hours ago) and read 5552 times:
Quoting VuelingAirbus (Reply 6): Spacing of landing traffic is double or more in actual low visibility operations
...Lawson was referring to the approximate doubling of the normal Cat I spacing between aircraft when they fly Cat III ILS approaches or, as the Europeans describe them, low-visibility procedures (LVPs). The additional spacing is required because aircraft on final during an ILS approach create signal multipath disturbances to the localizer beam, which, depending on the shape and size of the aircraft can last many seconds, and even minutes, before becoming stable again. Call it electronic wake turbulence.
This effect was dramatically demonstrated at London Gatwick Airport some years ago when a Swissair MD-80 requested a practice ILS autoland on a VFR day while following a Boeing 737 on final. All went well until the MD-80 was crossing the threshold, just as the 737 exited the runway and presented its vertical fin broadside on to the ILS localizer transmitter at the stop end of the runway. At 50 ft, the MD-80 went into a steeply banked right turn as its autopilot attempted to follow the localizer, which had been momentarily reflected off the centerline by the 737, and only quick action by the crew avoided a disaster."
Quoting A350 (Reply 7): IS it an urban legend or is it true that the cars and trucks at the motorway at FRA are also disturbing the ILS signal?
.."Frankfurt’s Runway 25R ILS currently has a notam describing random but severe interference that affects its ILS guidance, and advises extreme operator caution. The interference is thought to come from a nearby satellite cable TV transmitter, but the airport authority is reportedly finding it difficult to prove that this is the source of the problem.
Several years ago, it was forecast that many ILS installations in Europe could be down-categorized due to expected interference from commercial FM broadcast stations operating just outside the ILS frequency band, and which were about to be allowed to increase their transmitter power. As a result, the Europeans mandated the carriage of interference-rejecting ILS receivers in aircraft operating in their airspace. Before the mandate went into effect, pilots frequently reported hearing rock music and radio commercials while listening for the ILS idents at certain European airports."
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
Thanks for that I was just wondering whether aircraft all lined up to land could cause problems for the aircraft behind on finals, but it appears not, sounds like it is just something for aircraft on the ground to beware of.
You are wrong. It is a huge problem. Spacing of landing traffic is double or more in actual low visibility operations
It seems to me you are talking about different things here. Spacing is increased for CAT-II/III operations in order to have the protection area on the ground cleared in time before the next landing clearance is issued. This both takes longer in really bad visibility (maneuvering is more difficult) and concerns a larger area as conditions deteriorate.
I have never heard of the aircraft flying on (final) approach posing a threat to the ILS signal for those behind them. This is mainly related to the distance to the antennae, as mentioned before.
Forgot to mention, there is a phrase regarding practice CAT-III approaches: "All the elements are available". This means the ILS at that moment supports CAT-III operations and the protection area will be clear in time. In the described case, clearly not all of the elements were available.