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Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
Surely LNAV+V must be safer? Many aviators know that the Garmin 650/750 equipment can be upgraded with a low or no cost software change to offer LNAV+V. This would seem like a substantial safety improvement to me, however the people at CASA appear to make out that LNAV+V does not improve safety over the existing RNAV, and it is really required to be Baro-VNAV. However the ATSB report on Lockhart River states:
Quote: “There were 49 respondents who reported that they had been involved in an incident involving RNAV (GNSS) approaches. The most common … was commencing the descent too early due to a misinterpretation of their position.” If you have LNAV+V installed, the actual descent doesn’t start until the GPS position in the database complies with the start of the (normally) 3 degree approach path. That means, when following the glide slope indicator, either manually or coupled, it would not be possible to start the descent early. In that case, isn’t it clear that LNAV+V provides a safety advantage over basic RNAV?Yes, I accept that Baro-VNAV is even better and allows a lower minima, but there are only a limited number of approaches in Australia with Baro-VNAV and in some aircraft the cost would be quite expensive to upgrade. In the case of the Garmin 650/750 equipment the cost is either zero or very low to upgrade the software of existing units.
Join Date: Jul 2000 Location: Sydney, Australia Posts: 430
Quote: however the people at CASA appear to make out that LNAV+V does not improve safety over the existing RNAV, and it is really required to be Baro-VNAV where is the evidence for this claim?
Quote: In that case, isn’t it clear that LNAV+V provides a safety advantage over basic RNAV? It is very clear. Where has it been claimed this is not the case?
Join Date: Jan 2004 Location: Here and there Posts: 2,861
Is anyone being prevented from using LNAV+V? Dash 8 operator I used to work for used advisory VNAV on normal RNAV approaches with standard RNAV minima. We still had to monitor limiting steps and so on but it worked very well and made for a very low workload approach. I agree that early descent is a real issue with the current standard of RNAV approach, particularly when tracking via the straight in fix. Using the dog leg rather than the straight in provides additional cues about your position in the approach. I know of many people who have descended, or been about to descend, early on a straight in RNAV. Agreed that any vertical guidance is better than none.
Join Date: May 2006 Location: Australia Posts: 457
Yes, it is. No one has said you can't use it. Just be educated on what it is, and more importantly, what it isn't. What is your point?
Join Date: Mar 2005 Location: America's 51st State Posts: 254
From CAAP 178-1(2) "however the people at CASA appear to make out that LNAV+V does not improve safety over the existing RNAV, and it is really required to be Baro-VNAV". Please provide evidence of this... The way the CAAP reads is that you can use VNAV but you just need to monitor your descent profile to ensure you don't descend below a limiting altitude. Extract from the CAAP paragraph 4.4.5 sates: "Some non-APV (NPA) avionics have a VNAV function that displays the vertical path in an ILS-like fashion. In these instances the vertical information is simply a mechanised representation of the designed approach path angle and is not linked to any external vertical navigation source and does not indicate the aircraft’s true relationship with the ground. If the approach chart line of minima indicates S-I or LNAV, then any VNAV indication provided by the avionics is advisory only. 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.".
Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
Ftrplt and alphacentauri, I agree that CASA has not said you can’t use LNAV+V, however every letter I get back is relatively negative. Here are a couple of quotes from letters I have received from Mr Carmody. Firstly, on 3 April 2018:
Quote: “I am advised that the type of LNAV+V equipment that you highlight presents an average descent profile based on the length of the approach and the altitude to be lost. It does not consider any obstacles or terrain at the location, nor does it consider whether the average profile displayed will cause a descent below the approach steps. For this reason, CASA guidance … specifically warns pilots not to rely solely on LNAV+V information for their descent … ” In a letter from Mr Carmody dated 24 January 2018:
Quote: “…some aircraft systems provide advisory vertical guidance (e.g. LNAV+V) which is not certified and based on a GPS derived vertical position … the slope from which the advisory vertical guidance is derived is not subject to certification of the vertical path and may not be within prescribed vertical limits.” For some reason Mr Carmody is clearly getting advice from others (as Mr Carmody does not have an aviation background) which show no enthusiasm for LNAV+V. Never in any of the letters that have come back to me do they mention that at a minimum, the LNAV+V has a starting point for the descent incorporated in the database. This makes it a lot more difficult to start descending early if the vertical guidance is going to be used.In all of the replies, CASA just keeps going on about Baro-VNAV, when the cost is far higher for fitment in most cases, and there are not that many Baro-VNAV approved approaches so far.
Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
VH. 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. This surely must reduce the chance of starting the descent too early. Are they suggesting that a company like Garmin would provide a descent profile that runs into a mountain? Gad. They must be more amateur than I thought.
Join Date: May 2006 Location: Australia Posts: 457
The CAAP makes no mention of it because it is untrue. You need to educate yourself on what your seeing on your display and what it actually means.
Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
I have just been informed that the CASA problem with LNAV +V is that it is not ICAO accepted! The astute Americans have gone and introduced this as it clearly improves safety in a low cost way.
Join Date: May 2006 Location: Australia Posts: 457
LNAV + V is a Garmin specific term for vertical advisory. Read your manual
Join Date: Jan 2004 Location: Here and there Posts: 2,861
None of those letters say you can’t use it Dick, they’re just saying you must use alternative means to confirm you’re profile, ie GPS distance plu baro altitude. Advisory VNAV is fine just dont use it as your sole profile reference.
Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
So you imply that you can use Baro VNAV as a sole reference.. you could die!
Join Date: Jan 2004 Location: Here and there Posts: 2,861
Emotive arguments do you no favours Dick. I will try to remember not to engage with you again. Good bye.
Join Date: Mar 2005 Location: America's 51st State Posts: 254
Dick, You wonder why people get short with you! You're either trying to stir up trouble or perhaps have no idea, but in this instance I'll go with the stir up trouble because of the stupidity of some of your statements e.g. "Are they suggesting that a company like Garmin would provide a descent profile that runs into a mountain? Gad. They must be more amateur than I thought.". Aerocat, well said Last edited by VH-MLE; 6th Apr 2018 at 03:51. Reason: Comment to AerocatS2A
Join Date: Mar 2002 Location: Seat 0A Posts: 8,257
Quote:
Originally Posted by Dick So you imply that you can use Baro VNAV as a sole reference.. you could die! Baro-VNAV is an approved standard. If you're aeroplane is certified for it, you probably won't die.Do I sniff a whiff of a republic?
Join Date: Jul 2000 Location: Sydney, Australia Posts: 430
Baro V-Nav approaches are designed and coded differently to 'basic' RNAV approaches. When a Baro V-Nav approach is loaded into a certified avionics system - yes, you can fly solely off the vertical glidepath with no requirement to monitor intermediate steps (in fact there aren't any intermediate steps beyond glidepath capture), you wont fly into a mountain (as long as the temp is within the certified bounds and accurate QNH is available). 'Basic' R-Nav are not coded with a vertical glidepath to 50ft (usually) over the threshold, they are designed with intermediate altitude steps vs distance. Therefore, no avionics manufacturer can build a vertical glidepath capability that can be solely relied upon as the data is not designed into the approach, and therefore not coded into any database, hence the advisory nomenclature. The FAA say no different to CASA in relation to use of advisory VNAV.
Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
Alphacenturi, fascinating. You state
Quote: “The CAAP makes not mention of it because it is untrue.” Let’s look at the approach plate for Goulburn RNAV-Z (GNSS) RWY 04.I point out whether the LNAV+V descent starts at an actual GPS position, or is interpolated back from another GPS position, it has exactly the same result – that is, a dramatic improvement in safety.
Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
Ftrplt. I am clearly not the risk taker you and your CASA friends are I would never rely solely on the glide slope - even on a baro VNAV approach- once had the indicator stick!
Join Date: Jul 2000 Location: Sydney, Australia Posts: 430
Quote: it has exactly the same result – that is, a dramatic improvement in safety. so what is the point of this pointless thread?
Quote: Ftrplt. I am clearly not the risk taker you and your CASA friends are Clearly you have no clue
Join Date: Jul 2001 Location: Australia Posts: 4,944
Folks, You all really know what Dick is getting at, that "CASA" actively discourage the use of some of the features of GARMIN (and some others) that internally enables the generation of a VNAV path, by whatever name. Of course, we (I hope) understand that you have to monitor and fly the printed letdown, as designed. Which I hope you would (monitor, that is) be doing even if you had a baro-VNAV or SBAS/GBAS VNAV procedure available. What gets me ( I don't know if Dick is even aware) but a coterie of FOIs "very very actively" discourage, all on the basis of "unapproved", but in reality, in my opinion, because they have nil/little actual real time knowledge and experience with what is on the market, and what so many are using in the real world. Tootle pip!!
Page 2Dick, Baro VNAV is very onerous for both the pilot and owner of the aircraft. Here is an extract from a recent CASA Flight Safety article: Crew training As well as having a suitably equipped aircraft, each member of the flight crew must have a current instrument approach procedure endorsement. This includes approved training in how to safely conduct a baro-VNAV operation, including: use of baro-VNAV instrument approach charts, including LNAV/VNAV minimums, temperature limitations, and vertical flight path angle principles of baro-VNAV vertical guidance, including path display and depiction and the effect of temperature use of MDA and DA for LNAV and LNAV/VNAV minimums respectively approach procedure selection from the relevant onboard navigation database barometric pressure (QNH) selection (altimeter subscale setting), and cross checking and verification procedures, including effect of incorrect setting VNAV mode selection and monitoring VNAV failure modes and mode reversions VNAV flight tolerances. Other requirements the GNSS navigation database must be valid, and the entire approach procedure capable of being loaded into the system the pilot must verify that the approach in the system is in accordance with the approach chart for two-pilot operations, the same barometric altitude from two independent sources must be displayed, and one must be in each pilot’s primary field of view the aerodrome must have a promulgated ICAO PANS-OPS design-compliant baro-VNAV approach procedure the aerodrome needs to have accurate aerodrome QNH and temperature available through either an aerodrome air traffic service, an aerodrome weather information services (AWIS) or automatic terminal information services (ATIS). Approved approaches: The Airservices Australia website lists aerodromes at which baro-VNAV approaches have been approved, validated or are planned. It also shows locations at which baro-VNAV approaches cannot be made, because the aerodrome has an unsuitable approach alignment, has been deregistered or has no local QNH or temperature available. Where a baro-VNAV approach is available, the RNAV GNSS chart will specify that the aerodrome QNH and temperature are required, and the temperature range under which the procedure can be flown. For the RNAV GNSS RWY 32L approach at Launceston, for example, the temperature range is minus 5 to plus 61 degrees Celsius. The actual path flown by the aircraft will depend on the ambient air density. A temperature higher than ISA will result in a steeper approach path; conversely temperatures lower than ISA will result in a lower descent profile. Where temperature and aerodrome QNH are temporarily unavailable, the LNAV-only approach must be used. So when it comes to GNSS approaches—don’t ‘push your own baro’. If you want vertical guidance, make sure you are properly equipped, trained and that the approach is approved for where you’re going. Airservices will also have a vested interest in this:The implementation of Baro-VNAV approaches is to be funded through normal industry cost recovery arrangements administered by Airservices using the same mechanism as that used to fund procedures maintenance. Baro VNAV will not be permitted at aerodromes without an AWIS and those that do will not necessarily have much lower minimums than LNAV. The aircraft barometric system will also have to be compliant. SBAS will not require any of this b******t. Modern navigators have this capability already, most if not all minima are 200' and all the pilot needs is a 3D endorsement. WAAS is the US version of SBAS and is far superior to Baro VNAV. It is possibly an option over there, but I do not read of anyone using it. As I type the Government is requesting submissions from aviation interests for the 2019 budget. GeoScience wants it and if we are blasé about this then SBAS will be available for other industries, but not for aviation due to further certification requirements. Just because the airlines have their collective heads up their a**e over this does not make it right. If you would like the appropriate person to contact regarding this then please PM me. You probably know him already.Please put your efforts toward SBAS. Last edited by Jenna Talia; 14th Apr 2018 at 12:10. Page 3
Join Date: Jul 2000 Location: Sydney, Australia Posts: 430
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.
Join Date: Mar 2002 Location: Seat 0A Posts: 8,257
At the risk of thread drift, re LPVs, Jenny Tailer said:
Quote:
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?
Join Date: Mar 2003 Location: The Dirty South Posts: 426
Quote:
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.
Join Date: Aug 2004 Location: moon Posts: 3,426
Quote:
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.
Join Date: Mar 2003 Location: The Dirty South Posts: 426
Quote:
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.
Join Date: Nov 2005 Location: Zulu Time Zone Posts: 729
Dick Smith:
Quote: 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.
Quote: 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...
Quote: 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.
Join Date: May 2006 Location: UK Posts: 40
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?
Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
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.
Join Date: Feb 2007 Location: Darwin, Australia Age: 51 Posts: 406
Quote:
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? 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.
Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
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!
Join Date: May 2005 Location: QLD - where drivers are yet to realise that the left lane goes to their destination too. Posts: 2,859
Quote: 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.
Join Date: May 2006 Location: Australia Posts: 457
^^^^^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;
Quote: 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 [email protected], 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?
Thread Starter Join Date: May 2002 Location: Australia Posts: 4,450
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?
Join Date: May 2005 Location: QLD - where drivers are yet to realise that the left lane goes to their destination too. Posts: 2,859
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.
Quote: 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.
Join Date: Nov 2001 Location: Australia/India Posts: 4,395
“More than likely”? Why? How did those jets at Mildura make it? Serious questions.
Join Date: Aug 2004 Location: moon Posts: 3,426
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.
Join Date: May 2006 Location: Australia Posts: 457
The jets in Mildura flew the approaches as temp compensated baro vnav. Not +v. 2 different technologies, that provide 2 different paths in space.
Join Date: May 2006 Location: Australia Posts: 457
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.
Join Date: May 2005 Location: QLD - where drivers are yet to realise that the left lane goes to their destination too. Posts: 2,859
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.
Join Date: Nov 2001 Location: Australia/India Posts: 4,395
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.)
Page 4
Join Date: May 2005 Location: QLD - where drivers are yet to realise that the left lane goes to their destination too. Posts: 2,859
I chose "more than likely" because that is more than likely the outcome. The two jets at Mildura were both appropriately equipped, and both crewed by two experienced, current, instrument rated, CRM trained pilots, who knew what they were doing, and even then the Virgin aircraft only got in by the skin of its teeth. How do you think Joe Bloggs will go, especially if the terrain isn't "very flat"? |
On a gps with waas capability, what is the significance of “lnav+v” being displayed?
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