Flagstaff ILS Runway 21

[FDXDave]

I'm curious to why the localizer has a 3 degree off set?
What's the point in an ILS in a low visability appr if the system won't even line you up with the runway?
The minimums are radar alt of 300 feet. Not much time to manuver if its foggy.
I mean from what I've read about ILS systems, they are not cheap. So if your going to buy
One then why have it off the center line lol.
I first thought the nav data was wrong. But nope.
Thanks,
Dave

[Ray Salmon]

My guess is going to be the terrain to the north of the localizer at 9300 ft is causing the ILS to be offset. An ILS is allowed to have up to 3 degrees of offset in the US in order to be called an ILS. Any more than that and it becomes an LDA approach and I suspect the minimums go up a bit.

[Keith Smith]

I'm curious to why the localizer has a 3 degree off set?

Probably for terrain.

ILS allows for up to 3 degs offset before it's deemed an LDA approach.

What's the point in an ILS in a low visability appr if the system won't even line you up with the runway?

This implies the approach has no use. The job of an instrument approach is to get down through the weather to a point from which a normal landing can be made. This approach still achieves that goal and has minimums that are lower than a non-precision approach. It's doing its job nicely.

You can assume that if terrain/obstacles would've permitted, they would've made it perfectly straight in. The fact that they didn't implies that there is terrain/obstacles somewhere within the protected area which required them to slightly offset the course.

[rtataryn]

The ILS at my home field (KSFF) RWY22R is offset 3 degrees due to terrain. Never been a problem. It gets us down for a normal landing even at minimums of 270 ft agl.

[FDXDave]

And this is why i asked. Never thought about the terrain at the higher approach altitudes. Now it makes sence.
In a GA aircraft to manuver at the 300 RA would be no problem. But a 767 might be a different story lol . But then again planes that big wouldn't fly into this airport i guess. So yes I'm glad i asked. Now I'm better prepaired. Thanks for all your answers. : )
Dave.

[Peter Grey]

Having flown this approach IRL a few times it's noticeable but not an issue for anything short of a turbine.

There's a 14000' mountain which is just close enough to the north to not allow the straight in.

Fun fact, 3 degrees is the maximum offset for an ILS.

[FDXDave]

Cool. I'm guessing the Airport Developer messed up. Could of just moved over the runway a few feet instead lol.

[Keith Smith]

Fun fact, 3 degrees is the maximum offset for an ILS.

Funner fact, this is the 3rd time it's been stated in this thread

[Scott Medeiros]

And this is why i asked. Never thought about the terrain at the higher approach altitudes. Now it makes sence.
In a GA aircraft to manuver at the 300 RA would be no problem. But a 767 might be a different story lol . But then again planes that big wouldn't fly into this airport i guess. So yes I'm glad i asked. Now I'm better prepaired. Thanks for all your answers. : )
Dave.

A 3° offset wouldn't require excess maneuvering for an airliner either. Take a look at the LDA Z for runway 19 into DCA http://155.178.201.160/d-tpp/1804/00443LDAZ19.PDF, which airliners (up to 757s) routinely fly. The LDA is offset 40°, with minimums of 707' AGL. This is due to the prohibited (P56) airspace north of the airport. Fun fact, if the LDA was offset by less than 3°, it would be an ILS.

[FDXDave]

And this is why i asked. Never thought about the terrain at the higher approach altitudes. Now it makes sence.
In a GA aircraft to manuver at the 300 RA would be no problem. But a 767 might be a different story lol . But then again planes that big wouldn't fly into this airport i guess. So yes I'm glad i asked. Now I'm better prepaired. Thanks for all your answers. : )
Dave.

A 3° offset wouldn't require excess maneuvering for an airliner either. Take a look at the LDA Z for runway 19 into DCA http://155.178.201.160/d-tpp/1804/00443LDAZ19.PDF, which airliners (up to 757s) routinely fly. The LDA is offset 40°, with minimums of 707' AGL. This is due to the prohibited (P56) airspace north of the airport. Fun fact, if the LDA was offset by less than 3°, it would be an ILS.

I've actually flown that approach in an Airbus. Looking at the chart it was obvious the appr was not even close to being lined up. The runway is 186 degrees and the appr is 145. The part that got me, but I understand now, is that I thought previously that all ILS approaches were straight in. No dogleg at all. There is also a GPS appr into DCA which follows the river. That is what I usually use now to fly into the Airport. I like the winding into the runway. Plus there are two runways, so you have to be on top of things to make sure you line up with the right one..So I've heard cough cough lol.