rationale for two panel mounted GPS

blueskyMD

blueskyMD

Pre-takeoff checklist
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Bigfoot297
I have been looking at some planes on TAP and many of them have two panel mounted GPS but no PFD. I never understood the reason for that. I was told that you can copy the flight plans from one to another , and its a back up etc but I have been flying with 530 for many years and never felt a need for second GPS. Now if someone has excess amount of money it would be OK but I would install an electronic PFD on the panel before investing in second GPS system.
 
If I had 2, I would use one to fly my flight planned route, and use the other for emergency use. I would set it up for a Direct to an IAF leading to low minimum GPS approach to a long runway at a multi service airport for my wife to use on the autopilot on GPSS guidance.
 
It’s a luxury but it is nice. Map on #1 flight plan up on #2. Or cross track on an approach.


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The people I know like to have one setup with a clear view of the route and map and the other showing traffic and weather over the route and map. The redundancy is nice but the GPS receiver it's self is so reliable anymore that I don't think it's needed. You are more likely to loose total electrical power which will render both useless.
 
Grum.Man said:
The people I know like to have one setup with a clear view of the route and map and the other showing traffic and weather over the route and map. The redundancy is nice but the GPS receiver it's self is so reliable anymore that I don't think it's needed. You are more likely to loose total electrical power which will render both useless.
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I do like how some of the newer stuff has backup batteries (though most of that is experimental only, I think.) Built in UPS! Which is only good if your AI is also immune to electrical system failure.
 
Redundancy, same reason many turbine level planes have dual transponders.

It’s also common to have the map on the top GPS and the flight plan or nearest on the bottom GPS.

There are some other more advanced things you can do to depending on your other equipment
 
James331 said:
Redundancy, same reason many turbine level planes have dual transponders.

It’s also common to have the map on the top GPS and the flight plan or nearest on the bottom GPS.

There are some other more advanced things you can do to depending on your other equipment
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The dual transponders are a requirement to be RVSM. A little different than choosing to have two GPS.
 
Grum.Man said:
The dual transponders are a requirement to be RVSM. A little different than choosing to have two GPS.
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Many planes that don’t use the RVSM also have them, no transponder can make you AOG depending on location and weather
 
Grum.Man said:
The dual transponders are a requirement to be RVSM. A little different than choosing to have two GPS.
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Are you sure? Two altimetry systems, sure - but two transponders? Not really in a position to look it up, but I didn’t think dual transponders were required...
 
kayoh190 said:
Are you sure? Two altimetry systems, sure - but two transponders? Not really in a position to look it up, but I didn’t think dual transponders were required...
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Given the statement bellow I am not sure how you would comply without twin transponders.

TWO INDEPENDENT ALTITUDE MEASUREMENT SYSTEMS Each system should be composed of the following components: (a) cross-coupled static source/system, with ice protection if located in areas subject to ice accretion; (b) equipment for measuring static pressure sensed by the static source, converting it to pressure altitude and displaying the pressure altitude to the flight crew: (c) equipment for providing a digitally encoded signal corresponding to the displayed pressure altitude, for automatic altitude reporting purposes; (d) static source error correction (SSEC), if needed to meet the performance criteria for RVSM flight envelopes; and (e) signals referenced to a flight crew selected altitude for automatic control and alerting. These signals will need to be derived from an altitude measurement system meeting the performance criteria for RVSM flight envelopes.
 
kayoh190 said:
Are you sure? Two altimetry systems, sure - but two transponders? Not really in a position to look it up, but I didn’t think dual transponders were required...
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Stick your head in any airliner cockpit, never saw one with only one. And that was before RVSM.
 
Because the SL30 was so expensive that installing a second 430 was a rounding error in the total project.
 
James331 said:
Redundancy, same reason many turbine level planes have dual transponders.

It’s also common to have the map on the top GPS and the flight plan or nearest on the bottom GPS.

There are some other more advanced things you can do to depending on your other equipment
Click to expand...

With airlines, you can't tell your paying passengers that you had to divert to podunk airport because the transponder was acting up, so now they have to take the bus from here. The redundancy allows the airline to continue to their original destination. That's a business-critical requirement.

For part 91, if my 530 fails in IMC, I'll divert to the nearest VMC and land. Given how rarely they fail, and the low frequency of flying compared to part 121, its sensible to use redundancy only on mission-critical items such as fuel pumps or magnetos; not GPS or transponders.
 
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Grum.Man said:
Given the statement bellow I am not sure how you would comply without twin transponders.

TWO INDEPENDENT ALTITUDE MEASUREMENT SYSTEMS Each system should be composed of the following components: (a) cross-coupled static source/system, with ice protection if located in areas subject to ice accretion; (b) equipment for measuring static pressure sensed by the static source, converting it to pressure altitude and displaying the pressure altitude to the flight crew: (c) equipment for providing a digitally encoded signal corresponding to the displayed pressure altitude, for automatic altitude reporting purposes; (d) static source error correction (SSEC), if needed to meet the performance criteria for RVSM flight envelopes; and (e) signals referenced to a flight crew selected altitude for automatic control and alerting. These signals will need to be derived from an altitude measurement system meeting the performance criteria for RVSM flight envelopes.
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But looking at this AC: https://www.faa.gov/documentlibrary/media/advisory_circular/ac 91-85.pdf there's also this:

(2) One Secondary Surveillance Radar (SSR) Altitude Reporting Transponder. If only one is fitted, it should have the capability for switching to obtain input from either altitude measurement system.

Which says to me that while each altitude system needs to have a pressure altitude output to a transponder, only one transponder is actually needed. Of course, I don't think I've ever seen an airplane capable of RVSM flight only be fitted with one transponder so it’s sort of a moot point. :)

Paulie said:
Stick your head in any airliner cockpit, never saw one with only one. And that was before RVSM.
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Oh I’m sure - although I try to avoid airliner cockpits. The guys up there can be such insufferable asshats!
 
blueskyMD said:
I have been looking at some planes on TAP and many of them have two panel mounted GPS but no PFD. I never understood the reason for that. I was told that you can copy the flight plans from one to another , and its a back up etc but I have been flying with 530 for many years and never felt a need for second GPS. Now if someone has excess amount of money it would be OK but I would install an electronic PFD on the panel before investing in second GPS system.
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PFDs have only been available for retrofit for the past decade or so. Before that, anyone wanting to spend an insane amount of money on avionics had to get dual GPS!

That, and if it's a 430 (ie Nav/Com/GPS), like someone else mentioned, a plain old nav/com is WAY too expensive for what it is, so it often makes the price of a second GPS worthwhile.
 
The thing is, you really need 3 panel mounted GPS units to ever really know where you are. If there's 2 and they disagree you can't be sure which one is wrong. Hopefully with 3 you'll at least have 2 that agree.

And I fully agree on the Nav/Comm price thing. I'm thinking of eventually moving from the 530W/430W pair I have now to something newer. Maybe a single GPS and a Nav/Comm, but the damn things are 3000-4000 new.
 
Under 135 we need two for class B nav out west where you are often outside of VOR service volumes.


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sarangan said:
With airlines, you can't tell your paying passengers that you had to divert to podunk airport because the transponder was acting up, so now they have to take the bus from here. The redundancy allows the airline to continue to their original destination. That's a business-critical requirement.

For part 91, if my 530 fails in IMC, I'll divert to the nearest VMC and land. Given how rarely they fail, and the low frequency of flying compared to part 121, its sensible to use redundancy only on mission-critical items such as fuel pumps or magnetos; not GPS or transponders.
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It’s not just airlines.

Professional flying in general demands redundancy whether 121, 135 or 91.

When you are flying part 91 Corporate, you don’t want to have to tell the HNWIs in the back that you have to divert to the nearest VMC airport because the GPS failed. That doesn’t go over so well....
 
gsengle said:
It’s a luxury but it is nice. Map on #1 flight plan up on #2. Or cross track on an approach.
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That's exactly how I used to have it set up in the avadyne SR20... nice to have
 
Fearless Tower said:
It’s not just airlines.

Professional flying in general demands redundancy whether 121, 135 or 91.

When you are flying part 91 Corporate, you don’t want to have to tell the HNWIs in the back that you have to divert to the nearest VMC airport because the GPS failed. That doesn’t go over so well....
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Or medevac
 
chartbundle said:
And I fully agree on the Nav/Comm price thing. I'm thinking of eventually moving from the 530W/430W pair I have now to something newer. Maybe a single GPS and a Nav/Comm, but the damn things are 3000-4000 new.
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Keep one of them (whichever you have room for) as your #2. I've seen quite a few GTN 750/GNS430W combos. And they still crossfill flight plans and such.
 
I have two,they where in the airplane when I bought it. Keep the 530 on map,the 430 on traffic.
 
frfly172 said:
I have two,they where in the airplane when I bought it. Keep the 530 on map,the 430 on traffic.
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Not a bad plan. I've been thinking ahead to how I'll fly when we have the TXi upgrade completed - Right now, we have a GTN 750 and I find that I switch pages on it more frequently than I'd like. It's just not ideal to have everything on one screen, because, for example, traffic is best seen when zoomed way in while weather planning is best done zoomed way out.

With the TXi, we'll have the 750 display, the TXi MFD, and the TXi HSI to display things on. My thought is to have the HSI zoomed in pretty close - 5-10 miles - and have the stuff that will kill you in the next couple of minutes on it. Traffic, terrain. The TXi MFD could be more medium-range, maybe have autozoom turned on but restricted to no more than maybe 50nm, track up to focus along the flight path, and showing lots of detail and possibly weather. Then, the GTN could be zoomed way out and show weather and anything else more in the long-range planning area. I'd probably keep it North Up too.

I wonder how long it'll be before I want a second display for the TXi? :rofl:
 
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