Hi Folks -- Of the 3050 ILSs in section four of my copy of nav.dat, 404 of them, i.e. more than 13% of them, are reversible. That's 202 pairs, if you want to count by pairs. -- In all such pairs, both ends use the same frequency. -- In all such pairs, the two ends have different IDENT codes. -- In all such pairs, the localizers face in opposite directions. -- In all such pairs, with two dubious exceptions, the localizers are documented to be more than 1km apart.
Here are a few examples Airport freq LOC-LOC distance EGPH: IVG 06 == ITH 24 (108.90) 1.817 nm KJFK: IHIQ 04L == IIWY 22L (110.90) 1.646 nm KJFK: ITLK 13L == IRTH 31R (111.50) 1.953 nm KLAX: IGPE 06R == IHQB 24L (111.70) 2.044 nm KLAX: IUWU 06L == IOSS 24R (108.50) 2.099 nm KLAX: IMKZ 07R == ILAX 25L (109.90) 2.270 nm KLAX: IIAS 07L == ICFN 25R (111.10) 2.263 nm KPHL: IPHL 09R == IGLC 27L (109.30) 2.065 nm KPHL: IVII 09L == IPDP 27R (108.95) 1.898 nm The whole list can be found at http://www.av8n.com/fly/reversible.txt There are several reasons why the two ends of such a pair must be considered _different_ ILSs, and cannot be operated simultaneously: 1) First of all, you have to ask where the localizer transmitter sits. The rule is that they sit a little ways beyond the departure end of the runway. If you tried to use a transmitter at the departure end of runway 6 to serve approaches to runway 24, the LOC course width would go to zero long before you reached the threshold of runway 24. There is no way this would go unnoticed. Also, locating the localizer transmitter at mid-field is out of the question. 2) Secondly, if you tried to serve two reciprocal runways with the same localizer, one or the other of them would be reverse sensing. There is no way this would go unnoticed. 3) If you tried to operate two transmitters at the same time, they would interfere. In particular, the outbound (missed approach) segment of one would ruin the inbound (final) segment of the other. Also there would be no way to make sense of the IDENT. And FWIW, I have experienced this first-hand. Sometimes a student is capable of forming an unshakable expectation that he will be using runway 6 right. He has the approach plate already out. He listens to the ATIS, but ignores the part about "landing and departing runway two seven left". He IDENTifies the ILS, hears "some" code, and assumes it is the right code, even though it's not. I tell him to double-check the IDENT, whereupon he double-checks the frequency, and sure enough the frequency is right. He has a real hard time getting established on the localizer, because it is reverse sensing ... not to mention various other problems. I explain to the long-suffering controller that my student got out the wrong approach plate, and we need to go hold somewhere and sort things out. The student overhears this, and still doesn't understand what went wrong, because he is absolutely sure that there is no such thing as a reversible ILS. In contrast, a skillful instrument pilot does not really need to know or care about reversible ILSs, because the wording of the ATIS and the wording of the clearance suffice to tell him which approach plate to use. I remark that section 4-7-13 of FAA 7110.65P, which specifies the duties of air traffic controllers, briefly mentions some procedures for "Switching ILS/MLS Runways". ------------------------------------------------------------------------------ Come build with us! The BlackBerry® Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9-12, 2009. Register now! http://p.sf.net/sfu/devconf _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
