Surely LNAV+V must be safer?

[ftrplt]

LNAV/VNAV only ever means BARO, if you have LPV the minima block is LPV.

The + V is purely avionics generated, no change to approach design or approach coding.

[Capn Bloggs]

At the risk of thread drift, re LPVs, Jenny Tailer said:

Originally Posted by JT

SBAS will not require any of this b******t.

My question: if LPV gets it's altitude/profile info from the SBAS, what is used to define the Missed Approach point, which is charted as a "DA" on the FAA charts. If one were to use an altitude, wouldn't one use the aircraft altimeter, in which case an accurate QNH must be used, in which case an AWIS/ATIS would be required?

[JPJP]

Originally Posted by ftrplt

The + V is purely avionics generated, no change to approach design or approach coding.

Exactly. This is also the source of my concern with Dicks questions. There’s a difference between real regulatory terms (LNAV/VNAV etc.) and branded terms (+V).

It seems that a manufacturer of avionics starts labeling a feature of their hardware, then pilots who aren’t familiar with the industry wide norms believe that it’s actually real. It’s just branding gibberish made up by a manufacturer. Similar situation to BMW, Porsche etc, all calling their stability, suspension and safety systems something different. It doeasnt mean that PASM is an industry norm, or you’re going to find a PROF box on a Jepp chart.

[Sunfish]

Originally Posted by JPJP

Exactly. This is also the source of my concern with Dicks questions. There’s a difference between real regulatory terms (LNAV/VNAV etc.) and branded terms (+V).

It seems that a manufacturer of avionics starts labeling a feature of their hardware, then pilots who aren’t familiar with the industry wide norms believe that it’s actually real. It’s just branding gibberish made up by a manufacturer. Similar situation to BMW, Porsche etc, all calling their stability, suspension and safety systems something different. It doeasnt mean that PASM is an industry norm, or you’re going to find a PROF box on a Jepp chart.

There is now a feature on some EFIS that allows a pilot to input altitudes at waypoints and allegedly use these to provide vertical guidance to the autopilot. I expect the technology to become common. To me this is like a child playing with razorblades.

[JPJP]

Originally Posted by Sunfish

There is now a feature on some EFIS that allows a pilot to input altitudes at waypoints and allegedly use these to provide vertical guidance to the autopilot. I expect the technology to become common. To me this is like a child playing with razorblades.

Generally, its prohibited to alter the altitudes/waypoints on an Instrument Approach within a FMS. Sometimes the altitudes on a STAR are altered from an At/Above to a hard altitude. Purely as a matter of technique, and depending on airframe and the company operations manual et, etc. (as I’m sure you know)

The technology has been around for a while, depending on the hardware. I agree with the razor blade euphemism. It’ll end in tears.

[oggers]

Dick Smith:

Yep. That was I.

Since then the price appears to have gone from $50 to $150 m and Baro VNAV does almost the same job at hardly any cost..

A post on the previous thread said. “ airlines don’t need WAAS so will not willingly pay for it”

Sounds logical to me.

But I would like to see a proper cost benefit study that also
looks at the non aviation users.

What the airlines will willingly pay for isn't much use for judging the benefit that SBAS will bring to GA. All SBAS needs in any region is one or two geo-stationary satellites and a few ground reference stations. The benefit is then ILS like approaches that cost the airport the same as a bog standard LNAV. No need to install and maintain costly ILS infrastructure.

There are already over 4000 LPV approaches in the US. You can also fly the existing LNAV/VNAV approaches to the DA without baro-vnav equipment or cold temperature restricition. You have to be blind to not see that SBAS APVs are the way ahead.

the people at CASA appear to make out that LNAV+V does not improve safety over the existing RNAV

...and yet it took google all of 0.42 seconds to return the following from CASA:

"Australian NPAs are published with a constant angle approach path, which clears all minimum altitudes, and facilitates the use of a stabilised descent technique...
...the constant angle stabilised approach technique is the recommended flight technique for all aircraft.....
...Some non-APV (NPA) avionics have a VNAV function that displays the vertical path in an ILS-like fashion.....If this type of vertical advisory
information is used, the pilot is responsible to ensure that the minimum segment altitudes published on the approach chart are adhered to.
"

It has been standard in the airline world and recommended for GA to fly using the CDFA technique for some time now.

Note how the CASA CAAP makes no mention of the fact that in such a VNAV. approach that there is an actual GPS position in the data base that starts the continuous descent.

There isn't a position in the database to start the CDFA. The point at which the unit thinks you will start the descent depends on what altitude it thinks you are at, which isn't very accurate without SBAS.

[VFR-Seek and Destroy]

Will the Garmin give the option of a LNAV+V approach when the pilot is selecting an approach if it not in an area with a SBAS?
Not based in Oz but does Oz have a SBAS?

[Dick Smith]

LNAV +V is not just branding gibberish. It gives a substantial improvement in safety.

15 people could be alive today if the aircraft in the Lockhart River accident had been so equipped.

[werbil]

Originally Posted by VFR-Seek and Destroy

Will the Garmin give the option of a LNAV+V approach when the pilot is selecting an approach if it not in an area with a SBAS?
Not based in Oz but does Oz have a SBAS?

Australia does have a trail SBAS operational, but TSO'd equipment is programmed to prevent it's use.

The GTN 750/650 normally gives the +V guidance in Oz, the exception seems to be some runways where there is a LNAV/VNAV approach.

Agree that 3D advisory guidance would most likely have prevented Lockhart River.

Surprised that no one has commented on the other nifty feature 'visual approaches' that came with the same update for the GTN 750/650. It gives you 3D advisory guidance to any runway in the database. Obviously it doesn't ensure terrain clearance, but it does give you a nice three degree slope to 50' above the threshold.

And for anyone that's wondering, from observation the calculated glide path on both +V and visual approaches is accurate enough to show the affects of temperature at ISA +15 on barometric altitude.

[Dick Smith]

Yes. The Visual approach provision in the latest Garmin units is incredible. I reckon in an emergency if locked above IMC to ground level and no where else to go it would very likely get you on the runway. Even better if coupled to the A/P.

It even works on the grass cross strips at places like Goulburn!

Suggest everyone who can gets the software update. Probably free!

[Traffic_Is_Er_Was]

15 people could be alive today if the aircraft in the Lockhart River accident had been so equipped.

15 people could be alive today if the crew of the aircraft had been capable of using what it was equipped with.

[alphacentauri]

^^^^^THIS^^^^^^ Is the crux of 3 pages of discussion.

I've no issues with +V. The issue I have are the people who don't understand how it works.


Werbil, I have some questions regarding your post;

from observation the calculated glide path on both +V and visual approaches is accurate enough to show the affects of temperature at ISA +15 on barometric altitude.

Did you have to set OAT on your equipment?
How do you know it was showing affects of temp...and not something else? (genuinely curious) Not trying to be a smart@rse, but I wasn't aware that +V took into account any temperature.

Questions for everybody.
1. Using +V with no external information sources where do you think the GPS gets altimeter information from? (I'll give you a hint it is not referenced to MSL)
2. Provided you know the answer to question 1, do you know what the difference between MSL and +V altimetry is? (Hint it is not a fixed number in Australia)

Can someone in Perth who uses +V tell us what the +V profile reads when doing RNAV approaches in SW WA?

Any survey lidar pilots on here? Has the GPS altitude for you lidar runs ever been the same as the barometric altitude shown on the altimeter? Is it different depending on whereabouts in Australia you are?

[Dick Smith]

Traffic. One of the most common form of fatal accidents by professional pilots is a CFIT.

Do you believe you would never make such an error?

How do you know?

[Traffic_Is_Er_Was]

Thousands of pilots are alive because they don't make such errors. They are trained and competent in the equipment they use. Pilots who are not trained or not competent will kill themselves and their passengers no matter what equipment they carry, especially if they are lulled into a false sense of security that the equipment will do all the work for them.

I reckon in an emergency if locked above IMC to ground level and no where else to go it would very likely get you on the runway.

It will more than likely just get you to the crash site.

[Lead Balloon]

“More than likely”? Why?

How did those jets at Mildura make it?

Serious questions.

[Sunfish]

Alphcentauri makes a good point about the approximation of the geoide (shape of the earth) that is used to calculate GPS altitude - it can be hundreds of feet out, at least that's what I've seen).

However, I would have thought that the error would be constant for the position. That means it can be removed by adding or subtracting an offset to the GPS altitude for the given approach and airport.

I note that apparently the latest experimental EFIS from MGL has the ability to construct a home built GPS approach and Dynon is under pressure to do the same.

How this new technology is going to be managed is difficult for me to understand, although the Australian regulatory response, predictably, will be blanket prohibition of having anything to do with it, which is not a good solution given human frailty. I am aware of the owner of at least one fully kitted RV's who boasted about his occasional alleged illegal IFR exploits thanks to his sophisticated EFIS and autopilot.

[alphacentauri]

The jets in Mildura flew the approaches as temp compensated baro vnav. Not +v. 2 different technologies, that provide 2 different paths in space.

[alphacentauri]

Sunfish, yes an SBAS approach has the geiod difference at the approach thld coded. Add this to the superior vertical accuracy of WAAS and a geometrically precise vertical path can be supplied.

[Traffic_Is_Er_Was]

Was that not the crux of the incident? That they were lucky to make it to the ground? That they should not have been in that postition ie. in an emergency above/in IMC to the ground with no where else to go? And we are talking about 737 drivers, not some enthusiast poking around in his Tobago, who decides to shoot some bodgy virtual ILS.
I actually took Dick's comments to be aimed at more the well equipped VFR pilot who has pushed his luck.

[Lead Balloon]

Of course they shouldn’t have been in that situation in the first place and yes they were ‘lucky’. But there is the ‘luck’ of a coin toss and there’s the ‘luck’ of lotto numbers. Why did you choose “more than likely” as the probabilities of a crash rather than arrival?

A VFR stuck on top is stuck on top. A plan to arrive at an aerodrome that looks like it’s surrounded by very flat terrain, using all available technology, seems better than waiting for fuel exhaustion, trimming for best glide and hoping.

(Alpha has noted a technical difference - thanks.)