Why is LDA RWY 33 at KMTN LDA (and not an ILS) approach ?

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Joegoersch

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JoeGoersch
Looks to be lined up with Rwy. Final approach course is 326 degrees and rwy is 326 degrees per chart supplement. Any thoughts ?
 
I believe its due to obstacles very close in.
 
weilke said:
I believe its due to obstacles very close in.
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I see them on the plate, but the DH is pretty low (250 ft). I didn't know obstacles close in made an ILS a LDA ???
 
Joegoersch said:
I see them on the plate, but the DH is pretty low (250 ft). I didn't know obstacles close in made an ILS a LDA ???
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There used to be this poster 'aterpster' who could quote chapter and verse on why this makes sense. I believe it is the 181ft obstacle right abeam the departure end of the runway that precludes an ILS.
 
Glide slope appears to be about 3 degrees, PLASI is 4 degrees...sailboats with +50 ft masts in the waterway at the approach end.

Probably what Wielke said...close in obstacles. It's not just to minimums, but the approach path has to be clear to the runway for an ILS.
 
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Ain't never seen an LDA with glideslope before. Here's my wild azz guess. The localizer is a cheap, not quite as accurate as a real localizer kinda like the old SDF's. I ain't bettin any more than one beer on that. @aterpster is still around.
 
I think I got it figured out. There is a LOC RWY 15 Approach. The localizer frequency is the same for both 15 and 33. Rather than have 33 be a Backcorse Approach the found a way to change the left right sensing so it appears normal to us when they change Runways. Because the Localizer antenna is at the far end of the runway, it's width at the threshold for 33 is wider than it would be for a localizer that is at the Approach end so they gotta call it an LDA. My bet has gone from one beer to one craft beer

Edit: disregard, I don't think that's it. Looks like the Localizer is closer to the end of 33 than 15. But it's off to the side. The final approach course for 15 is 144 and the runway heading is 146.5. It can bring you down to the centerline of the runway at the threshold with only a 1.5 degree offset. On 33 the final approach course is 326 and the runway heading is 326.5. To have the localizer take you to the centerline at the threshold would be a steeper angle because the antennae is so close to that end of the runway. So they parallel the extended centerline off to the right what looks like about 250 feet.
 
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luvflyin said:
Edit: disregard, I don't think that's it. Looks like the Localizer is closer to the end of 33 than 15. But it's off to the side. The final approach course for 15 is 144 and the runway heading is 146.5. It can bring you down to the centerline of the runway at the threshold with only a 1.5 degree offset. On 33 the final approach course is 326 and the runway heading is 326.5. To have the localizer take you to the centerline at the threshold would be a steeper angle because the antennae is so close to that end of the runway. So they parallel the extended centerline off to the right what looks like about 250 feet.
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+1

The offset from the centerline is what makes is an LDA
 
Obstacles don't usually make so
luvflyin said:
Ain't never seen an LDA with glideslope before. Here's my wild azz guess. The localizer is a cheap, not quite as accurate as a real localizer kinda like the old SDF's. I ain't bettin any more than one beer on that. @aterpster is still around.
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Plenty with glideslope. KFYV has one (I've flown it) as does DCA. Others, too. (I think ROA does, but not sure, I've just flown GPS into ROA).
 
luvflyin said:
Edit: disregard, I don't think that's it. Looks like the Localizer is closer to the end of 33 than 15. But it's off to the side. The final approach course for 15 is 144 and the runway heading is 146.5. It can bring you down to the centerline of the runway at the threshold with only a 1.5 degree offset. On 33 the final approach course is 326 and the runway heading is 326.5. To have the localizer take you to the centerline at the threshold would be a steeper angle because the antennae is so close to that end of the runway. So they parallel the extended centerline off to the right what looks like about 250 feet.
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If it's really significantly off to the side, I'd bet that's the reason. :thumbsup:

Martha's voice keeps echoing in my head... "Localizer DARN angle!!" :D :D
 
luvflyin said:
Ain't never seen an LDA with glideslope before. Here's my wild azz guess. The localizer is a cheap, not quite as accurate as a real localizer kinda like the old SDF's. I ain't bettin any more than one beer on that. @aterpster is still around.
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An LDA localizer is supposed to be the same as a regular LOC. The approach is designated LDA because it is either not aligned with the runway or other operational reasons (as in this case). It's not uncommon to have glidslopes on LDAs. The LDA Y 19 (formerly the Roslyn LDA) at DCA not only has a GS, it is REQUIRED. It's also the case that the end of the approach is not only not aligned with the runway, it ends 3.4 miles away from the runway.
 
flyingron said:
An LDA localizer is supposed to be the same as a regular LOC. The approach is designated LDA because it is either not aligned with the runway or other operational reasons (as in this case). It's not uncommon to have glidslopes on LDAs. The LDA Y 19 (formerly the Roslyn LDA) at DCA not only has a GS, it is REQUIRED. It's also the case that the end of the approach is not only not aligned with the runway, it ends 3.4 miles away from the runway.
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Yeah, there are more than just a couple of them out there. I'm not seeing that the glideslope is required for DCA's LDA Y 19. It has both S-LDA/GS and S-LDA minimums. They're both the same but you can fly it without GS
 
Martin is my home airport and have flown the LDA 33 quite a few times, fairly certain you are correct in that it's because the LOC is off to the side of the runway.
 
FLYGUYRY said:
Martin is my home airport and have flown the LDA 33 quite a few times, fairly certain you are correct in that it's because the LOC is off to the side of the runway.
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It looks like it puts you halfway between the runway and the parallel taxiway. Is that about right?
 
luvflyin said:
It looks like it puts you halfway between the runway and the parallel taxiway. Is that about right?
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Yup! I've never flown it below a simulated 500 foot ceiling but I think that's about where you would end up if you took it down to minimums
 
FLYGUYRY said:
Yup! I've never flown it below a simulated 500 foot ceiling but I think that's about where you would end up if you took it down to minimums
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Have you ever looked at the needle while making a VFR straight in to see exactly how much deflection would put you on centerline?
 
I flew from Martin for years, yes it is an LDA because it is offset. Yes, they have to switch it back and forth between 15 and 33 and the tower is always happy to do it for practice in vmc. At minimums, you end up just slightly lined up on the grass, like one 172-wing offset. If you ever visit there, taxi to "Strawberry Point", which is directly off the side of 33. The Martin museum has a static display of some interesting airplanes there which are only accessible from airside. The museum itself is on the main ramp in one of the hangars adjacent to the tower/fbo building, which is an Art Deco masterpiece in its own right.
 
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