Vertical path non-precision approach safety?

[derg]

I'm not seeing the McGuffin here. It seems like flying that approach in "dive and drive" mode would be just as safe as flying it in "sorta VNAV" mode, to me. Conceivably...dare I say it...safer?

Maybe.

We dove and drove for years.

However, on the MD-88/90 we had to do a "double punch" technique because sometimes it would get a little "sloppy" and not capture the altitude correctly. So between the auto throttles being two little 'drama queens' (full power! CLMP! full power! LO LIM! all in the same sentence) and potentially lazy altitude captures, it makes it a wild donkey show for the passengers and turned out to be a bigger workload than:

1. Select and set the approach.
2. Dial the next 100' above TCH
3. Hit LNAV (or LOC)
4. Hit VNAV
(magic)
5. Land to revelrous applause.

 

[derg]

Well, I'll just say that I think that you're a trusting soul. There are worse things to be, for sure.

Well, if you can fly 3:1 from your final approach fix to the MDA, you know where you should be in your head, cross reference that with the vertical deviation from Progress Page 2, back it up with the VPATH and have situational awareness, it's really simple.

Come jumpseat with me into JFK one day where we do NP approaches regularly. I'll show ya! (for real)

 

[dasleben]

Well, I'll just say that I think that you're a trusting soul. There are worse things to be, for sure.

He is, because that's the way the airplane is designed. It's constantly updating its position information from any number of sources until you drop it into manual mode and inhibit the airplane's ability to update its IRU position reference.

 

[Boris Badenov]

Ok, let's make sure we're all talking about the same stuff, here, then. There are GPS approaches which are certified for LNAV/VNAV mins, and there are GPS approaches which are certified for LNAV mins, but one's "FMS/FMC/Bundle'o'wires" can portray a "glideslope" which will, presumably, carry them down this computer-generated pseudo-glideslope. What are we talking about, because I know to an absolute certainty that they both exist.

 

[dasleben]

Ok, let's make sure we're all talking about the same stuff, here, then. There are GPS approaches which are certified for LNAV/VNAV mins, and there are GPS approaches which are certified for LNAV mins, but one's "FMS/FMC/Bundle'o'wires" can portray a "glideslope" which will, presumably, carry them down this computer-generated pseudo-glideslope. What are we talking about, because I know to an absolute certainty that they both exist.

Well, we can use LNAV/VNAV because...we have VNAV.

http://jeppesen.com/download/aopa/apr00aopa.pdf

If it's just LNAV, we treat it as an MDA, adding 50 feet, and still use the VNAV as long as there's a descent angle published on the chart (and it coincides with the angle shown in the FMC). We coo?

 

[Boris Badenov]

I can't say that I've ever seen anyone monitor cross radials on one of these approaches, but it's not a terrible idea.

I'm not saying I do it at Hartsfield in clear and a billion, but any DPE worth his salt would fail you for your Instrument ride if you didn't. Food for thought, at least?

 

[dasleben]

I'm not saying I do it at Hartsfield in clear and a billion, but any DPE worth his salt would fail you for your Instrument ride if you didn't. Food for thought, at least?

Without giving a dissertation on 767 systems, I can tell you that there isn't really a way to accurately do that in this thing, at least without compromising the position updating. You can toss them into the FIX page on the FMC, but it'd just show your little airplane on the map mode crossing a computer-generated line. It'd just be clutter at that point.

 

[derg]

Ok, let's make sure we're all talking about the same stuff, here, then. There are GPS approaches which are certified for LNAV/VNAV mins, and there are GPS approaches which are certified for LNAV mins, but one's "FMS/FMC/Bundle'o'wires" can portray a "glideslope" which will, presumably, carry them down this computer-generated pseudo-glideslope. What are we talking about, because I know to an absolute certainty that they both exist.

Well, at my carrier, we can only use that "follow it down to DA(MDA)" on approaches like this:

The FMS knows to compute a 3.14 degree VPATH and respect the VDP.

However, we can fly a VNAV approach down to a DDA (Derived Decision Altitude), generally MDA +50 feet on an approach like this:

Crap, can't find one, but if you look at the approach procedure, it says "Only authorized operators may use VNAV DA(H) in lieu of MDA(H)" so this approach is a perfect example of the 'circle of trust'.

Some will say "Not Authorized" and others, like a VOR-A, hell, it's a circling maneuver anyway so some of us have to be VMC so it's moot.

The real fun is when it comes to turning RNP approaches with RF legs into somewhere like Quito, Ecuador. I'll try to find that one.

 

[Boris Badenov]

We're clearly trains passing in the night at this point. And I'm sure that it's my failure to understand what you're saying that's the problem. If you have legit vertical guidance (as I said like two pages ago), use it. It still seems more than just rational to me to tune the cross radials, etc, but I'm a Nerd, as I already admitted to. But if you're flying an LNAV approach with artificial (ie. non-certificated) vertical guidance (which we could certainly do even in the early-90s tech Bitchjet), then, IMHO, you now have an obligation to be treating it as an a non-precision approach...because that's what the TERPS say it is. Does that clear anything up, at all?

 

[Deleted member 27505]

Just wondering what others have experienced.

Check the approach plate for the VNAV or LPV (or whatever GPS vertical you were tracking). Do the notes for it say "VGSI and glideslope not coincident"? You can sometimes get the situation you described if the glideslopes are not aligned.

 

[dasleben]

We're clearly trains passing in the night at this point. And I'm sure that it's my failure to understand what you're saying that's the problem. If you have legit vertical guidance (as I said like two pages ago), use it. It still seems more than just rational to me to tune the cross radials, etc, but I'm a Nerd, as I already admitted to. But if you're flying an LNAV approach with artificial (ie. non-certificated) vertical guidance (which we could certainly do even in the early-90s tech Bitchjet), then, IMHO, you now have an obligation to be treating it as an a non-precision approach...because that's what the TERPS say it is. Does that clear anything up, at all?

And I'm telling you it's fully certificated, and is nothing like your ghetto-assed bitchjet VNAV.

And our tech is from the early 80s!

 

[derg]

Here's one that will kick your ass if you're not pre-briefed on it.

Gotta go missed before an "RF" leg? TOGA, then ya better hit LNAV immediately or you're going to "S'cuse me, while I kiss the volcano"!

Fun as hell to fly in the simulator at night, when you'd be flying it, and then turning on the visuals in simulated day VMC to see what you're actually doing.

They'd always give us nasty crosswinds too.

Then "CHECK RNP" or "VERIFY POSITION" would pop up on the FMS head right before an RF leg and hilarity ensues.

 

[derg]

Check the approach plate for the VNAV or LPV (or whatever GPS vertical you were tracking). Do the notes for it say "VGSI and glideslope not coincident"? You can sometimes get the situation you described if the glideslopes are not aligned.

We have a flow chart!

 

[derg]

This is a very interesting thread!

 

[Boris Badenov]

And I'm telling you it's fully certificated, and is nothing like your ghetto-assed bitchjet VNAV.

And our tech is from the early 80s!

And I'm telling you, nose of the bitch, that the Cray computers nestled in the nose of your flying beheamoth have screw-all to do with the sort of approach you're shooting, and what the regs require of you while flying it. Opspecs notwithstanding. If your Opspecs state that you can treat a certain kind of non-precision (by the terms of the FARs/AIM) approach as an a precision approach, I will not only retract my nasty comments, but buy you a beer at NJC. Otherwise, you're Rong...it's a non-precision approach and any special snowflakes you might be able to create with your friend the FMS are advisory only, and therefore you should be cashiered, your licenses sent ot OKC to be cut up and made in to dogfood, and you should probably be ritually stranged, just to be sure, if you aren't flying the approach AS a non-precision approach (eg. monitoring the DME and cross-radial bearings). May God have Mercy on your Soul.

 

[derg]

Some more interesting information about CDA's and even an interesting graphic.

From: http://code7700.com/cdfa.html

 

[dasleben]

And I'm telling you, nose of the bitch, that the Cray computers nestled in the nose of your flying beheamoth have screw-all to do with the sort of approach you're shooting, and what the regs require of you while flying it. Opspecs notwithstanding. If your Opspecs state that you can treat a certain kind of non-precision (by the terms of the FARs/AIM) approach as an a precision approach, I will not only retract my nasty comments, but buy you a beer at NJC. Otherwise, you're Rong...it's a non-precision approach and any special snowflakes you might be able to create with your friend the FMS are advisory only, and therefore you should be cashiered, your licenses sent ot OKC to be cut up and made in to dogfood, and you should probably be ritually stranged, just to be sure, if you aren't flying the approach AS a non-precision approach (eg. monitoring the DME and cross-radial bearings). May God have Mercy on your Soul.

C073 sucka, we haz it.

Ship it.

(I prefer IPA)

 

[Boris Badenov]

C073 sucka, we haz it.

Ship it.

(I prefer IPA)

Did I say anything about shipping poop? IF You show up at NJC with C073 pinned to your little sailor outfit and IF I find your parents to vouch for you, AND IF I find both it and them trustworthy, I'll buy you a Shirley Temple. Because you deserve it, for living this long doin it rong.

See you there, handsome!

 

[typhoonpilot]

Here's one that will kick your ass if you're not pre-briefed on it.

Gotta go missed before an "RF" leg? TOGA, then ya better hit LNAV immediately or you're going to "S'cuse me, while I kiss the volcano"!

Fun as hell to fly in the simulator at night, when you'd be flying it, and then turning on the visuals in simulated day VMC to see what you're actually doing.

They'd always give us nasty crosswinds too.

Then "CHECK RNP" or "VERIFY POSITION" would pop up on the FMS head right before an RF leg and hilarity ensues.

We used to have that issue in the B777, but then along came some upgrades and automatic TOGA to LNAV was born.

Prior to all our aircraft having TOGA to LNAV a technique that worked was just to hit ALT HOLD until the turn was finished then go TOGA. Depended on the reason for the missed approach, but certainly acceptable in terms of keeping one clear of terrain.


TP

 

[dasleben]

Did I say anything about shipping poop? IF You show up at NJC with C073 pinned to your little sailor outfit and IF I find your parents to vouch for you, AND IF I find both it and them trustworthy, I'll buy you a Shirley Temple. Because you deserve it, for living this long doin it rong.

See you there, handsome!

Oh, it's a man date.

And at least we don't have this RF witchcraft @Derg is talking about. Some kinda voodoo, that.