Vector Above G/S Intercept

[Everskyward]

^ Interested into the answer to this from a controller perspective. I've not yet ever received vectors to final on an RNAV approach, I've gotten vectors to an IF though, and always at an appropriate altitude.

I have received vectors to final on an RNAV approach but it was not LPV since we can't do LPV. It was an LNAV/VNAV to a DA.

 

[NoHeat]

I ask because it happened to me today.

It was the first time I attempted an LPV approach, but I just asked for RNAV. It was for rwy 25 at KIOW.

I was given vectors to the final approach course and told to maintain altitude of 3300 until established on the final approach course. Following these instructions, I found that I became established about 4 miles before the FAF. The profile view of the chart shows that I should be at only 2300 at the FAF, but there was no way for me to get that low so quickly. It seemed like an unrealistically rushed experience. Being new to LPV, I wasn't sure why this happened, and that is why I am wondering if I should have specified that I intended to use the LPV minimums.

 

[peerlesscowboy]

I ask because it happened to me today.

It was the first time I attempted an LPV approach, but I just asked for RNAV. It was for rwy 25 at KIOW.

I was given vectors to the final approach course and told to maintain altitude of 3300 until established on the final approach course. Following these instructions, I found that I became established about 4 miles before the FAF. The profile view of the chart shows that I should be at only 2300 at the FAF, but there was no way for me to get that low so quickly. It seemed like an unrealistically rushed experience. Being new to LPV, I wasn't sure why this happened, and that is why I am wondering if I should have specified that I intended to use the LPV minimums.

That's only 250' per nm, 500 fpm @ 120 kts.

 

[Henning]

IFR and we were visual the whole time. Broke through a very light cloud deck.

I thought it was extremely odd but didn't question it, which looking back was my mistake.

Yes it was, luckily you learned that without incident. Will you occasionally be asked to do something strange by ATC? Yes, it will happen, but it is your duty and responsibility to get clarification to make sure it is actually what they want, and if you don't think you can safely accommodate them, you have to tell them "unable." I always try to help out ATC when I can to keep everything flowing smoothly, but occasionally I have to give them a "sorry, unable".

Whenever you have a situation that is contrary to standard IFR procedure, you really need to question them on it, because occasionally ATC makes a mistake as well.

 

[Dihedral]

17, they did jam you a bit since you would normally be at 3300 about 7 miles from the FAF. The GS altitude at 4 miles from the FAF is 3500+ so you were below it. If they are vectoring me to the final, I want to intercept the final approach course at least 1 mile out for every 300 feet above the FAF altitude.

 

[NoHeat]

Okay, I must have been a little closer than four miles. What I definitely remember is that I was above the GS by about one dot when I got established. It doesn't matter.

The reason for my post is not to discuss whether I was four vs three miles etc on one particular flight, but to ask this more general question re. radio usage:

When I ask ATC for a particular RNAV approach, should I also state "LPV" to help ATC know what to do, in case they want to vector me on course?

 

[aterpster]

I ask because it happened to me today.

It was the first time I attempted an LPV approach, but I just asked for RNAV. It was for rwy 25 at KIOW.

I was given vectors to the final approach course and told to maintain altitude of 3300 until established on the final approach course. Following these instructions, I found that I became established about 4 miles before the FAF. The profile view of the chart shows that I should be at only 2300 at the FAF, but there was no way for me to get that low so quickly. It seemed like an unrealistically rushed experience. Being new to LPV, I wasn't sure why this happened, and that is why I am wondering if I should have specified that I intended to use the LPV minimums.

That would have been outside of HEWRI, which means a minimum altitude of 2,800 applied until HEWRI, not the LPV G/S. I realize you were likely well above 2,800 crossing HEWRI, but it is a restriction that has to be considered. In this case the LPV G/S should be almost exactly 3,300 at HEWRI, none the less 2,800 controls until the P-FAF.

 

[John Collins]

When flying an RNAV (GPS) procedure, you determine which minimums you fly it to based on your equipment capability and the annunciated approach mode. With a WAAS GPS, you may fly any procedure minimums which your AFMS permits as long as the annunciation is suitable for the procedure. So if it annunciates LPV, you may chose the fly the LPV, LNAV,VNAV, or LNAV minimums if they are on the chart. If you have filed a domestic flightplan, ATC has no way of knowing what the aircraft capabilities other than an indication that it is GPS equipped for at least enroute and terminal operation. As a result, they must follow their guidance and assume that the altitude provided satisfies any of the approach criteria, including LPV.

For a variety of reasons, I prefer to be cleared to a fix for an RNAV approach rather than receiving vectors to final. I also request a specific fix to join the approach and the vast majority of the times I am cleared direct to the requested fix. Regardless, once established on a segment of the procedure and cleared for the approach, the minimum altitudes to be used are the ones on the approach chart.

 

[Jaybird180]

I guess it's my mindset, but I cannot or will not respond to an actual issue of this nature without having the approach chart.

Based on the 2 Johns' argument, one says cannot the others says you will not

 

[poadeleted20]

If you ask for an RNAV approach, is it necessary to specify LPV if that is your intention, so that the controller will know to vector you out far enough that you are under the glideslope?

No, it is not.

c. For a nonprecision approach, at an altitude

which will allow descent in accordance with the​

published procedure.

With vectors to final, they still have to get you to where you can descend to the published segment altitude on nonprecision approaches (which, technically, an RNAV approach is even if flown in the LPV mode) before the intercepted segment ends without an excessive rate of descent (150 ft/nm desired, 318 ft/nm max -- see TERPS para. 242d), and with LPV, the intermediate segment altitude is the same as the g/s intercept altitude (ie., g/s intercept at that altitude at the FAF).

 

[poadeleted20]

I ask because it happened to me today.

It was the first time I attempted an LPV approach, but I just asked for RNAV. It was for rwy 25 at KIOW.

I was given vectors to the final approach course and told to maintain altitude of 3300 until established on the final approach course. Following these instructions, I found that I became established about 4 miles before the FAF. The profile view of the chart shows that I should be at only 2300 at the FAF, but there was no way for me to get that low so quickly.

1000 feet in 4 miles is 250 ft/nm, which while greater than the desired intermediate segment descent gradient of 150 ft/nm, is still under the maximum gradient of 318 t/nm, and thus it should not have been any trouble at all to "get that low that quickly".

It seemed like an unrealistically rushed experience. Being new to LPV, I wasn't sure why this happened, and that is why I am wondering if I should have specified that I intended to use the LPV minimums.

No, I think you should work on your basic instrument flying techniques so you can achieve a descent gradient of up to 318 ft/nm on the intermediate segment of an approach without any difficulty at all.

 

[poadeleted20]

Okay, I must have been a little closer than four miles.

Even at 3.2 miles, you should have been able to lose 1000 feet before the FAF without exceeding 318 ft/nm.

When I ask ATC for a particular RNAV approach, should I also state "LPV" to help ATC know what to do, in case they want to vector me on course?

That should not be necessary if the controller is doing his/her job properly and you can achieve the standards the FAA sets for executing these procedures.

 

[aterpster]

MVA is 2,500 except where noted: