copcar1988

Hi, I have two questions.

First, when doing a non-precision approach with a VDP, I know you can't descend until reaching it if you have the field insight, but if you do have the field insight, can you line up with the runway centerline before reaching the VDP? I ask this becuase not all non-precision approaches are exactly right on.

Second, if your shooting an ILS and you intercept the glideslope at 5000 ft, will that be your final approach fix now even if on the chart says you should intercept the glide slope at a lower altitude?

Thanks for the help,

copcar1988

JMT21

The VDP is not a reg, rather 'nice to know information'. If you look at 91.175, you will see you need 3 things in order to decend below your MDA/DA: 1) You must be in a continuous position to land 2) You must have the required visibility and 3) You must have the runway enviroment in sight. As I'm sure you are aware, on many approaches the missed approach point is the end of the runway. If you were to suddenly break out at several hundred feet AGL just short of the runway, you would not be in a continuous position to land. Thus, the VDP (Sometimes listed on the plate, or as calculated) acts as sort of a missed approach point-If you don't have the visibility or runway enviroment at that point, you will no longer be in a continuous position to land and might as well initiate a go around.
As to your actual question, I'm really not positive but would assume that as soon as you have the runway enviroment in sight you would be safe to line up with the runway. I will be interested to see what others say.

Glideslope intercept is always your final approach fix regardless of what the plate shows. The final approach fix as listed on the plate is for a localizer only approach.

rickair7777

121 is different...

Op Specs usually require that you utilize the VDP. Since Op Specs are regulatory, the VDP is regulatory.

You could break off the course guidance of a non-straight in LDA/SDF if conducting a visual approach. If conducting the published approach (non-circling) , you stay on the guidance at MDA until the plate indicates it's OK to do otherwise (ie VDP).

Also, you are required to utilze the visual glideslope (PAPI/VASI) in almost every case, and the VDP should roughly correspond to that.

JMT21

So what if there is no published VDP..are you required to compute one? Say your doing a VOR approach that brings you in 15-20 degrees left or right of center...when can you break off the published lateral portion of the approach in ordar to line up with the runway? (It shouldn't matter if there is published VDP or not if I understand correctly)

Herc130AV8R

When intercepting the ILS above the FAF altitude you may still want to hack a watch at the FAF for the localizer in the event you loose glideslope guidance and there is no DME. This will give you a back-up for determining the MAP. It's a good habit to still verbalize that you are passing the FAF for the localizer just in case.

Herc130AV8R

To compute a VDP take your HAT on the plate and divide it by the glideslope.
VDP=HAT/GS
Ex: 300/3.0=100
Move the decimal place back 2 place and you get 1 mile out for a VDP. Which makes sense since 1 mile at 300ft is a 3 degree glideslope.

rickair7777

If it is an instrument, not a visual approach, we are supposed to use a VDP based on 3 degrees if one is not published.

As far as the lateral guidance, I wouldn't break off before VDP unless the approach plate suggests otherwise. From VDP, you should have time to get centered up. I doubt there are any non-aligned non-precision approaches with super-low mins anyway....and if a VDP is published there is a reason for it.