GNX or GTN to equip your aircraft build for IFR?

hi Steve O'Connor with Midwest panel builders and today we're going to talk about navigating with GPS with radio navigation capability as opposed to GPS only so we have a lot of conversations with builders about which navigators to install on their panels whether they want to use units like the GTN 650 635 625 or the newer GNX 375 I think we need to start with a quick overview of the unit's themselves but first I'd like to start off by saying that in no way am I trying to change anybody's mind on this subject I'm just going to present some facts and let people decide on their own I do not push customers one way or the other because it's really up to them how they want to go any opinions that are in this video are mine and we may not agree and that's fine because what's good for me may not be good for you okay so let's start talking about the unit's themselves starting with the GTN 650 X I the GTN 650 X I is a wise GPS with Nav and comms capabilities built-in so not only can we navigate be a GPS but we also have the navigation radio which allows us to tune in ground-based navigational aids such as vor and ILS to not only navigate vor to Bo AR but also to perform vor ILS or localizer approaches the GTN 650 also has a built in comm radio like the GTN 650 the GTN 635 and GTN 625 are wise GPS units however neither will have the navigation radio built into them so you'll be navigating only by GPS the GTN 635 has a comm radio built in while the GTN 625 has no radio tuning and now to the GNX 375 this unit is similar to the GTN 625 and that it is a wise gps and it has no navicomp features however this is where the similarities end unlike the GTN series of navigators the GNX 375 has an 80 s be in and out transponder built into the unit this will save you a bit of cost which will break down a little later I think the next thing we need to look at are the legalities of equipping your airplane with a GPS only navigator okay so let's look at F AR 91 205 paragraph D instrument flight rules States for IFR flight the following instruments and equipment are required so while this section does list the required instruments D 2 is what we're interested in and it states way radio communication and navigation equipment suitable for the route to be flown so what exactly does this mean well when we look at 125 203 communication and navigation equipment we see section D use of a single independent navigation system for operations under IFR it states the airplane may be equipped with a single independent navigation system suitable for navigating the airplane along the route to be flown with the degree of accuracy required for ATC if it can be shown that the airplane is equipped with at least one other independent navigation system suitable in the event of loss of navigation capability of the single independent navigation system permitted by this paragraph at any point along the route proceeding safely to a suitable Airport and completing an instrument approach so the next question would be how does a single wise GPS receiver satisfy this requirement first we need to take a look at the Waze system and how it works unlike traditional ground-based navigational aids the Waze system has a more extensive coverage area so in simple terms a satellite has an atomic clock it sends out a signal with its position and timestamp to a GPS receiver that receiver takes that signal determine its position in relation to that satellite when you take more than one satellite you need three to actually triangulate you had a fourth one then and we get a three-dimensional position so the problem is is even with the atomic clocks we still have a discrepancy in time between the satellites and earth and we also have an ionosphere interference that will cause the signals to slow down which will also create a discrepancy this is where Waze or the wide area augmentation system comes to the rescue let's take a look at how Waze works wide-area reference stations are linked to form the u.s. wise network signals from GPS satellites are monitored by these wide area reference stations to determine satellite clock orbital and position Corrections each station in the network relays the data to a wide area master station where the correction information is computed than uplinked via a ground earth station to a geostationary satellite the message is then broadcast the Waze receivers within the broadcast coverage area in addition to providing the correction signal the wise geo satellite provides an additional range measurement to the aircraft receiver will also provide an additional GPS satellite and view the integrity of GPS is improved through real-time monitoring and the accuracy is improved by providing corrections to reduce errors this performance improvement is sufficient enough to enable approach procedures with GPS wise of vertical guidance so far the FAA has completed installation of three Geo satellite links 30 wide area reference stations three wide area master stations six ground earth stations as well as a required terrestrial communication to support the Waze network including two operational control centers so now that we have a better understanding of Waze let's look at the aeronautical information manual for clarification on the faa RS if we dig in a section one of the aeronautical information manual navigational aids and we look at paragraph eight Part C general requirements we see the following text GPS wise was developed to be used within the geo coverage over North America without the need for other radio navigation equipment appropriate to the route of flight to be flown outside the wise coverage or in the event of a wise failure GPS wise equipment reverse to GPS only operation and satisfies the requirements for basic GPS equipment so in this text it would appear that one wise GPS unit is considered two forms of navigation one being the Y assist 'm and ii the gps itself in the event of Waze failure now if we look at paragraph 9 it States unlike t SOC one two nine or nine was avionics which we're certified as a supplement to other means of navigation wise avionics are evaluated without reliance on other navigation systems as such installation of wise avionics does not require the aircraft to have other equipment or appropriate to the route to be flown so in short if your aircraft is equipped with a wise gps receiver is satisfies the requirements of 91 205 and 125 203 for required navigation equipment in your aircraft so now that we know it's possible to equip our aircraft with only wise GPS for navigation what are the arguments against this configuration the first and least common is a possibility of watch GPS outages and while there are areas that this can be a problem like near the edge of the wise coverage area for the vast majority of the u.s. this will never be an issue we can turn to the FAA website to look at the current wise coverage so another issue with GPS could be jamming whether it's intentional such as the military running operations or the individual that's trying to evade their boss so that they can't be GPS tracked by having a handheld jamming unit this is illegal it has happened at a few airports in the past it's very rare but the FAA and the FCC do actively look for this type of jamming so that they can eliminate the issue now in the instance of a military operation it is generally well 1 it's usually noted but generally does not affect pilots too often but if it does you would definitely need to contact DTC immediately and let them know that you're having a GPS issue and then they could notify the proper authorities to stop the jamming so let's assume for a moment that you did lose all GPS and you had no ability to navigate at that point all it's not lost because with the help of ATC we can do a few different approaches we can do an ASR approach which is non-precision and what you'll get lateral guidance with step downs along the way or we could do APA are if they're equipped which would be a precision approach and in this case we're going to get not only lateral guidance but we also get the vertical guidance down to the runway so in any event with ATC's help we definitely be able to navigate we haven't lost anything else we can still fly headings we can still do everything that we would normally do so really this isn't going to be an issue if you live in an area with a lot of GPS outages then the GTN 650 might be your choice the one caveat would be that you would actually have to find an airport with an ILS or vor approach and if it requires DME in order to identify points along that approach you might be out of luck since most of us still use the GPS is to identify those points on the approach so one of the arguments that we often hear about using a Waze only GPS is a single navigation source is in the flight planning and alternate selection this is in reference to the one-two-three rule when we are doing IFR flight planning the rule states that from an hour before to an hour after your scheduled arrival if the weather is forecasted to have a ceiling of less than 2000 feet with visibility less than 3 miles you have to file an alternate and that alternate must meet the following minimums for a precision approach procedure if the forecasted ceiling needs to be at least 600 feet with a visibility of 2 statute miles for a non-precision approach procedure the ceiling needs to be at least 800 feet with the visibility also to statute miles and again we'll turn to the aeronautical information manual for the requirements while using only wise GPS for navigation 9a States pilots with wise receivers may flight plan to use any instrument approach procedure authorized for use with their wise avionics as the planned approach it it required alternate however when using wise at an alternate Airport flight plan must be based on fly in the RNA of GPS l nav or circling minima and non precision weather requirements must be used for planning but it also states that upon arrival at an alternate when the wise navigation system indicates that L Navi nav or LP V service is available then vertical guidance may be used to complete the approach using the displayed level of service so the argument is that when you're flying with a wise only GPS that you might have to plan for extra fuel to fly to an alternate with the forecasted non-precision minimums while this may be true those flying for recreation do not have the same time constraints as those flying for business or commercial purposes so we can more easily make that go/no-go decision secondly even though I can't file a certain Airport on a flight plan because of the minimums I can fight any ultra and I want and I can fly the approach all the way down to the minimums prescribed for the approach that I am trying to fly so really this is only going to affect you in the flight planning portion so another concern that people have had is actually not GPS related but comm related so units like the GTN 650 and the 6:35 will have the calm built in while the 625 and the GNX 375 will not have calm when we use the GNX 375 for instance we typically install the gt-r 20 Calm radio this is a remote mounted radio that's controlled directly through the g3x screen the concern raised is that if the screen goes out you want to have control of the radio and while this statement is true and the unlikely event that you do lose a screen if you have a second screen that will allow you to still control the Calm radio however if you only had one screen or you lost both of those screens then the radio would failsafe to one 21.5 what you would allow you to still communicate with air traffic control since they monitor that frequency well I know that there are likely more arguments against flying it with a wise only GPS which I'm sure will hear in the comments these are the most common ones that we get so now that we've talked about what you can't do with Waze only GPS let's take a look at what you can do as of January 30th 2020 there are 4,000 48 Waze lpv approach procedures serving 1954 airports 1186 of these have no ILS there are also 724 localizer performance approach procedure serving 531 airports of which 429 do not have ILS an LP B approach oftentimes we'll have minimums that match that of an ILS while the LP approach is similar to a localizer only approach and most if not all the airports that have an ILS will have an LP V approach that's a lot of airport you can fly too without the need for an ILS and my home airport Lapeer we have three approaches the vor alpha and to our nav approaches but the iron nav approaches are the only ones that are straight in so the last question that needs to be addressed is why not just use a gteen 650 if it can do all the same our nav approaches as the GNX 375 plus an ILS or vor approach I mean it seems like a clear choice so it really comes down to one major difference and that's price with the added benefit of not having to install an antenna in the tail and the real estate that we gain on the panel which with everything we're trying to fit in the panels today that's actually consideration the GNX 375 is about 6/10 of an inch smaller in height than the GTN series now having designed a lot of panels I know that this is sometimes the difference in making everything fit some pilots especially those coming from certified aircraft will say that the smaller screen size makes it harder to use many times they ask for the GTN 750 because they want the bigger screen size which if you're putting this into a traditional steam gauge aircraft I can definitely understand the concern however when coupled with the g3 X system as is mostly the case with the experimental built aircraft these days and certainly with the panels we build that concern is no longer an issue 95% of the things you do with the GPS can be handled right from the g3 X directly you can change flight plans on the fly and send the changes to the navigator you can even transfer flight plans from for flight or Garmin pilot without the need for additional equipment like the flight stream I can honestly see a day in the not-too-distant future when the GPS will also become a remote mounted unit freeing up even more panel space now back to the biggest advantage which is price and it can be substantial when you compare the GT in 615 to the 635 or the 625 the savings is not as big with the pricing coming in around ten thousand nine hundred for the 650 ten thousand for the 635 and nine thousand four hundred for the 625 with the 625 actually being a little bit more than the 635 when you factor in a comm radio such as the gt-r 24 around $1,000 bringing the total to ten thousand four hundred dollars however with the GNX 375 we see a bigger savings the price new unit is around six thousand eight hundred but has the equivalent to a gtx 45 our transponder bulletin in the unit save an additional three thousand five hundred now if we factor in the cost of a remote mountain gt-r 20 we have a cost of around seven thousand eight hundred dollars as opposed to the GTN 650 x i which cost ten thousand nine hundred then we need to add the gtx 45 our to cost a three thousand five hundred to give us a total of fourteen thousand four hundred that's a potential savings of around six thousand six hundred which is quite substantial so the last point that I'll make is that if you're planning on getting your instrument rating in your airplane then you will need the GTN six 50 fer 60 165 requires three different approaches with navigational systems and the ACS still requires that you demonstrate precision and non-precision approaches so keep that in mind so which way you go really is down to personal preference if you like the security of having the ILS and BLR capabilities built-in and the GTN 650 is it gonna be for you if you're a little more budget minded and you're okay with the waz only GPS then the GNX 375 is also a great choice if you enjoyed this video and you'd like to see more be sure to subscribe to the channel make sure you hit that notification bell as well if you have any questions at all you can reach us at eight one zero three five six three eight five five you can also visit us online ww Midwest panels calm you

Channel: Midwest Panel Builders

Views: 65,273

Keywords: Avionics, Experimental Aircraft, Experimental Avionics, Garmin, Garmin Aviation, Garmin Avionics, G3X, Sling 2, Sling 4, Sling TSi, The Airplane Factory, GTN 650Xi, GNX 375

Id: vQZAm0EnBrc

Length: 16min 50sec (1010 seconds)

Published: Mon Apr 13 2020