RNAV approach NA at night at KHHR? Why?

[N1120A]

All - I came across this recently. I was setting up to fly the RNAV approach into KHHR, because it gives vertical guidance and I prefer WAAS accuracy and sensitivity to a LOC. Read the chart - NA at night, so had to fly the LOC. They are based on the same intersections, fixes and even have (by NOTAM) the same minimums. The RNAV approach is more accurate. Why would they do something so stupid like this. I get the reason for having higher than usual minimums and basically requiring WAAS to do the approach by NOTAM, because of the parallel approaches with LAX, but there is zero reason to make the better approach NA at night. You don't even have to have a ground based receiver in your airplane to fly IFR with a WAAS GPS, and this would basically make HHR unavailable below visual minimums for folks with that.

@aterpster ? Anyone else?

 

[Jim_R]

I can't answer, but you're not alone in wondering. I remember that the RNAV 14 to KDTN was NA at night for years (though I can't remember if the LOC 14 was also NA at night.) It's now okay at night, but there's a note (on both the RNAV 14 and LOC 14) that "Night landing rwy 5, 23, 32 NA". I do not know what, if anything, about the procedure changed from when it used to be NA at night.

 

[flyingron]

Usually, night restrictions on approaches are due to unlit obstacles in the approach area. Those approaches are strange due to the altitudes at HASHY and ZANIR as well. Perhaps, Wally can give us some insight.

 

[chemgeek]

I notice that the KHHR GPS 25 VGSI and RNAV glide slope are not coincident. The FAA has been reviewing approaches where this is the case, and this can result in the approach designated NA at night or with increased minimums. We've been through a lengthy process of discussion with the FAA about how to harmonize our VGSI and glide slope at KVGC to get lower LPV minimums consistent with the current safety requirements. We used to have a DH of 250 AGL and now it's around 450 AGL.

 

[RussR]

Unlit penetrations of what is known as the 20:1 visual surface is the usual cause of night restrictions. Another is lack of airport survey data.

For the specific answer in this case, you can contact the FAA directly at the email address at the bottom of this page:
https://www.faa.gov/air_traffic/flight_info/aeronav/procedures/

 

[iamtheari]

Does the FAA trust localizers more than WAAS at some point on the approach? WAAS has a margin of error that stays the same regardless of your distance from the airport, while the localizer narrows as you get closer.

Another possibility is that the localizer approach plate was last updated 07DEC17 while the RNAV plate was updated 05DEC19. Maybe there is a new issue that led to them updating the RNAV plate but the localizer plate hasn't been updated yet.

I'm shooting in the dark here, but those are the things that come to mind. I'm curious to learn more.

 

[RussR]

WAAS has a margin of error that stays the same regardless of your distance from the airport, while the localizer narrows as you get closer.

Course width on an LP or LPV narrows similarly to how a localizer does. Not due to physics (like the localizer), but due to being programmed that way.

 

[chemgeek]

Does the FAA trust localizers more than WAAS at some point on the approach? WAAS has a margin of error that stays the same regardless of your distance from the airport, while the localizer narrows as you get closer.

Another possibility is that the localizer approach plate was last updated 07DEC17 while the RNAV plate was updated 05DEC19. Maybe there is a new issue that led to them updating the RNAV plate but the localizer plate hasn't been updated yet.

I'm shooting in the dark here, but those are the things that come to mind. I'm curious to learn more.

Both the LPV and LOC approaches have virtually the same minima. The LOC has a VDP as well which may suggest possible obstructions close to the runway.

Our RWY 35 GPS approach is hampered by obstructions on the approach end, and a required climb gradient on the missed approach to miss windmills off the far end of the runway. Both of these are limiting the approach minima. The limiting factors can be complicated. We've been through 2-3 rounds of revisions of our approaches to mitigate obstacles that intrude on changing safety standards. Our RWY 17 approach got LOWER minima, while the 35 approach got much higher minima in the latest round of revisions. Go figure.

 

[iamtheari]

Course width on an LP or LPV narrows similarly to how a localizer does. Not due to physics (like the localizer), but due to being programmed that way.

I am referring to the physics, not the programming. At some point, there may be a cross-over where the real course of the localizer is narrower than for the LP/LPV. When closer to the localizer antenna than the cross-over point, there would be a wedge on each side where the plane with a centered LP/LPV needle would have full deflection on the localizer. An obstruction in those wedges could result in different rules between the two approaches.

But that's really a stab in the dark. The wedges where you have a more precise localizer indication than WAAS-based indication are probably extremely small. WAAS is accurate within 10 feet. I think you'd have to be parked dangerously close to the localizer antenna to have a narrower localizer signal than WAAS-based path.

 

[RussR]

I am referring to the physics, not the programming. At some point, there may be a cross-over where the real course of the localizer is narrower than for the LP/LPV. When closer to the localizer antenna than the cross-over point, there would be a wedge on each side where the plane with a centered LP/LPV needle would have full deflection on the localizer. An obstruction in those wedges could result in different rules between the two approaches.

But that's really a stab in the dark. The wedges where you have a more precise localizer indication than WAAS-based indication are probably extremely small. WAAS is accurate within 10 feet. I think you'd have to be parked dangerously close to the localizer antenna to have a narrower localizer signal than WAAS-based path.

Sure. But in practice, while WAAS may be accurate to within 10 feet, that doesn't mean that if you get 10 feet off course you're going to see any indication on the CDI. CDI scaling for a WAAS approach is designed to closely mimic that of a localizer. So if you flew an LPV approach to a runway that also had an ILS with both of them displayed on their own CDI, you should see pretty much the same deviations at any point along the approach.

The obstacle evaluation areas for LPV and ILS (and LP and Loc) are all-but-identical. Meaning the same obstacles would be evaluated for both.

 

[iamtheari]

The obstacle evaluation areas for LPV and ILS (and LP and Loc) are all-but-identical. Meaning the same obstacles would be evaluated for both.

That's what I'm clumsily getting at. Does the FAA trust WAAS enough to evaluate the same areas for obstacles close to the airport for LP/LPV approaches as for LOC/ILS approaches, where the real (not software-emulated) sensitivity increases as you get closer to the station? The quoted portion of your post answers that question in the affirmative.

So that leaves "outdated localizer approach plate" as my best guess on the OP's question.

 

[N1120A]

I can't imagine they'd leave the airport without an approach available at night, so there has to be some other reason. The LOC has no vertical guidance at all, while the LPV does have reliable vertical guidance after ZANIR.

 

[RingLaserGyroSandwich]

I can't imagine they'd leave the airport without an approach available at night, so there has to be some other reason. The LOC has no vertical guidance at all, while the LPV does have reliable vertical guidance after ZANIR.

Why? My home airport is like that.

 

[Clip4]

https://www.aopa.org/news-and-media/all-news/2016/june/20/not-authorized-at-night

 

[Tantalum]

I think the OP's point is that the path's are virtually identical.. with the only material difference being the MAP and the minimums allowed

Here are the plates in question.. the only thing I can think of is that the for the RNAV violates some kind of rule from the AIM.. basically what Russ said about about 20:1

However, if you can fly the RNAV during the day, or in hard IMC, down to minimums, without hitting anything, then why you can't do the same thing at night is completely beyond me.. (unless of course there is some obstacle beyond the MAP that's predicated on the pilot seeing it and avoiding it during the day.. however I find that unlikely).

 

[Tantalum]

^the best part about this, is that I bet you everyone flying this approach just loads the LOC into their 430 (insert GPS of choice) and flies it based on that "for reference only".. how many people are actually using their DME, or if they don't have one, dialing up VOR2 and looking at the Seal beach radials.. which, with a VOT accuracy that allows you to be a few degrees off I'm wondering if this approach is actually obstacle "safer" than the RNAV

 

[N1120A]

^the best part about this, is that I bet you everyone flying this approach just loads the LOC into their 430 (insert GPS of choice) and flies it based on that "for reference only".. how many people are actually using their DME, or if they don't have one, dialing up VOR2 and looking at the Seal beach radials.. which, with a VOT accuracy that allows you to be a few degrees off I'm wondering if this approach is actually obstacle "safer" than the RNAV

Also, by NOTAM, they have the exact same minimums, despite the vertical guidance on the RNAV that the LOC doesn't have.

Further, a GPS is a substitute for DME (the reason you need DME is to define the fixes). The reason for simultaneous reception of I-HHR and LAX DME is because I-HHR doesn't provide DME to define the step down fixes. A GPS deals with that, which essentially turns this approach into a GPS approach without vertical guidance - since you can use GPS navigation as primary so long as you are monitoring the LOC as well.

Which makes it even stranger that the more accurate RNAV is NA at night.

Wally @aterpster ??

 

[unsafervguy]

1. There is nothing that says you have to dive and drive a loc. Tune up the loc nav 2. Load the rnav. Use number 2 to insure you are on course and use the Vnav on rnav for decent. As long as you protect the crossing altitudes, your good.

 

[Clip4]

1. There is nothing that says you have to dive and drive a loc. Tune up the loc nav 2. Load the rnav. Use number 2 to insure you are on course and use the Vnav on rnav for decent. As long as you protect the crossing altitudes, your good.

The FAA does not support dive and drive approaches these days. With a little math and the decent angle of 3.10, 5x ground speed sets things up nicely.

 

[flyingron]

The horizontal flight path is the same. The final descent is different. The angle is different and so are the Maps. The LOC has you level out at the MDA for a while before hitting the MAP (even in the FAA non-dive and drive). The LPV has a decision height. You spend more time at 580 feet in the LOC version.

 

[iamtheari]

The horizontal flight path is the same. The final descent is different. The angle is different and so are the Maps. The LOC has you level out at the MDA for a while before hitting the MAP (even in the FAA non-dive and drive). The LPV has a decision height. You spend more time at 580 feet in the LOC version.

The MDA for the LOC and for the LNAV are the same. Couldn't they just say "LPV DA NA at night" if the decision height (and sinking through it while reconfiguring to go missed) were the issue? That would leave the LNAV MDA to be flown at night, which is much more similar to the LOC approach.

I also looked at the MAPs as you mentioned. That's a bigger difference. If you are on the LNAV, your MAP is the runway threshold. If you are on the LOC, your MAP is 0.8 nm earlier. Any chance there's an obstacle to the side of the approach path within the last mile?

Then again, I keep going back to the chart dates. I wonder if we'll see an Amendment 13 to the LOC that says "procedure NA at night." Two years is a long time for trees, buildings, radio masts, and power lines to grow, not to mention for policies to change.

 

[John Collins]

The FAA does not support dive and drive approaches these days. With a little math and the decent angle of 3.10, 5x ground speed sets things up nicely.

That is not true. I agree that many in the FAA express a preference for a constant angle descent final approach (CDFA), particularly for Turbojet aircraft, but there is no prohibition on using the dive and drive method, which is assumed in TERPS Non Precision Approach design and minimums. Using the CDFA technique requires both higher visibility minimums and use of a higher derived decision altitude than the MDA.

 

[John Collins]

The horizontal flight path is the same. The final descent is different. The angle is different and so are the Maps. The LOC has you level out at the MDA for a while before hitting the MAP (even in the FAA non-dive and drive). The LPV has a decision height. You spend more time at 580 feet in the LOC version.

And the circling minimums only apply if there is an LNAV minimum and procedure and is not applicable to LPV, ILS, LNAV/VNAV minimums. LNAV is not as precise as LOC and may be flown by a WAAS or non WAAS GPS. Also note that all procedures have the note "Circling NA when Control Tower closed". Both the VOR and the RNAV also have the note "Circling NA North of Runway 7-25" and the RNAV has the additional note "Procedure NA at night" which applies to all uses of the approach, not just circling. The RNAV chart also indicates that the 20 to 1 visual segment is penetrated by obstacles on RWY 25, which is consistent with not having a published VDA. The RNAV TERPS do not allow night operations when the visual segment 20 to 1 is penetrated with obstacles. The LOC approach has a narrower path to the threshold than the RNAV LNAV minima.

 

[RussR]

Has anyone contacted the FAA directly yet? That’s where the real answer will be found.

 

[Clip4]

That is not true. I agree that many in the FAA express a preference for a constant angle descent final approach (CDFA), particularly for Turbojet aircraft, but there is no prohibition on using the dive and drive method, which is assumed in TERPS Non Precision Approach design and minimums. Using the CDFA technique requires both higher visibility minimums and use of a higher derived decision altitude than the MDA.

I stated the FAA does not support dive and drive. When the FAA issues an advisory circular on a procedure, that becomes the procedure the FAA supports. I agree in the aircraft we fly it not needed, but neither is dive and drive. Something between works really well.

 

[tsts4]

I stated the FAA does not support dive and drive. When the FAA issues an advisory circular on a procedure, that becomes the procedure the FAA supports. I agree in the aircraft we fly it not needed, but neither is dive and drive. Something between works really well.

What's the number of the AC you are referring to?

 

[Clip4]

What's the number of the AC you are referring to?

AC120-108. You will also find stabilized approaches on 4-37 instrument procedures handbook. And yes the primary emphasis turbine aircraft, but applicable to piston aircraft.

 

[tsts4]

AC120-108. You will also find stabilized approaches on 4-37 instrument procedures handbook.

OK, thanks. However, I disagree with your opinion that the FAA does not support "dive and drive" just because they published this AC nine years ago.

 

[Clip4]

OK, thanks. However, I disagree with your opinion that the FAA does not support "dive and drive" just because they published this AC nine years ago.

ok, then show me an FAA document that supports getting down to the MDA an LOC quickly so you can drive in the clouds at 350 Ft AGL to the MAP.

 

[tsts4]

ok, then show me an FAA document that supports getting down to an MDA an LOC quickly so you can drive in the clouds at 350 Ft AGL to the MAP.

Show me the one for part 91 ops where the FAA says not to. I'm mean it's kinda inherent in the non-pression IAP design.

 

[Clip4]

Show me the one for part 91 ops where the FAA says not to. I'm mean it's kinda inherent in the non-pression IAP design.

The similar situation exists with landing over an obstacle. The FAA used to support two methods, today they only support the one with the most stabilized approach. The FAA supports the procedures they publish.

 

[tsts4]

The similar situation exists with landing over an obstacle. The FAA used to support two methods, today they only support the one with the most stabilized approach. The FAA supports the procedures they publish.

And yet you offer no evidence to back up this opinion. Just because you keep saying that's the FAA's position doesn't make it so.

 

[Clip4]

And yet you offer no evidence to back up this opinion. Just because you keep saying that's the FAA's position doesn't make it so.

If the FAA supports a procedure, they publish it so you can reference it. Can you show me an FAA publication that promotes entering a hold any way you like? You can certainly do it any way you like, but the FAA supports the entries as published in the AIM and there handbooks.

 

[tsts4]

If the FAA supports a procedure, they publish it so you can reference it. Can you show me an FAA publication that promotes entering a hold any way you like? You can certainly do it any way you like, but the FAA supports the entries as published in the AIM and there handbooks.

Again just because you say it’s so doesn’t make it so. To be clear I’m not stating the FAA “supports” the so called “dive and drive” procedure since that’s just a moniker for descending to and leveling off at the MDA. What I’m saying is IMO you chose the wrong verb and therefore insinuating that the FAA “approves” of only one method. YMMV....

 

[Dean V]

If you don’t like the Continuous Decent method, calculating your own VDP and an approximated descent rate to the VDP Is another option. The old dive down to the MDA and drive is rather out dated.

 

[chemgeek]

Before GPS, all you had for positional awareness on a non-precision approach was your stopwatch. (On a LOC approach, you might get a marker beacon to help out.) In this situation, if you didn't get down to the minimum altitude quickly, you might miss your chance to see the airport upon breakout, especially if flying in a tailwind. My home airport had a miserable VOR-A approach for years (now mercifully decommissioned) that involved flying at right angles to the only runway on an easterly heading in normally strong westerly winds. If one did not descend smartly from the FAF to the MDA, it was very easy to miss the airport. Usually a 700 fpm descent was sufficient, but on a windy day if you lolly-gagged at 500 fpm or less, you could easily fly past the airport before spotting it.

I really don't see the safety issue in a reasonable (say 700 fpm) descent to the MDA on a non-precision approach in order to give yourself plenty of time to find the airport and circle-to-land. As long as you stay at or above the designated approach altitudes, what is the issue? On the other hand, who flies non-precision approaches these days? Almost every airport now has an LPV approach. Not all, but many. However, if flying an LNAV approach, I will still smartly and controllably descend to the MDA when able, especially for circling approaches where finding the airport sooner than later may be important.

 

[Clip4]

Here a presentation

https://d2nvf92ef53i1o.cloudfront.n...t-Procedures-and-Charting-Updates-Trekell.pdf

 

[Palmpilot]

...On the other hand, who flies non-precision approaches these days? Almost every airport now has an LPV approach. Not all, but many....

There are a lot of rental Cessnas with a KLN94 GPS, which does not support LPV.

 

[chemgeek]

There are a lot of rental Cessnas with a KLD94 GPS, which does not support LPV.

That's a whole 'nother question. I crossed the WAAS Rubicon many moons ago. IFR is good on the other side.

 

[Clip4]

There are a lot of rental Cessnas with a KLD94 GPS, which does not support LPV.

Really?