Second GPS Unit

[Chrisgoesflying]

I am in the early planning stages for a panel upgrade on my Comanche, including making it IFR ready so I can get my rating in it. In Canada, one of the requirements says:

For the plane to be IFR legal, it must have:

• (j) sufficient radio navigation equipment to permit the pilot, in the event of the failure at any stage of the flight of any item of that equipment, including any associated flight instrument display,
  • (i) to proceed to the destination aerodrome or proceed to another aerodrome that is suitable for landing, and
  • (ii) where the aircraft is operated in IMC, to complete an instrument approach and, if necessary, conduct a missed approach procedure.

So, basically, if my IFR GPS fails, I must have some other means of navigation that would allow me to complete an approach and missed approach. My instructor said to just install two GPS units. Now, my plan is to install a really nice primary unit. But then for the secondary unit, I want to go on a budget. Would you install something like a KLN94 or one of the ancient, no color Garmins as a backup unit? I assume my iPad would not count as a "backup" - I think it has to be panel mounted. What about a panel mounted VFR unit as a backup, would that be legal?

Also curious, do the U.S. regs say something similar? If so, what did you do for backup navigation? Second GPS or something else?

 

[midlifeflyer]

But then for the secondary unit, I want to go on a budget. Would you install something like a KLN94 or one of the ancient, no color Garmins as a backup unit?

I would not. Your primary and secondary units would be so dissimilar that, unless you are very unusual, when the emergency occurred, you probably wouldn't remember how to use it properly. Unless, of course, you only relied on it for VLOC capability.

In the US, we have a requirement for an alternate means of navigation when we are using non-WAAS GPS. But I think that's about it. Canada's rules tend to be more conservative in some areas than ours for a good reason - you have far wider expanses of nothing than we do.

 

[Chrisgoesflying]

I would not. Your primary and secondary units would be so dissimilar that, unless you are very unusual, when the emergency occurred, you probably wouldn't remember how to use it properly. Unless, of course, you only relied on it for VLOC capability.

In the US, we have a requirement for an alternate means of navigation when we are using non-WAAS GPS. But I think that's about it. Canada's rules tend to be more conservative in some areas than ours for a good reason - you have far wider expanses of nothing than we do.

Hmm, my plan is to have a very capable WAAS GPS unit as primary. The secondary unit is really only there to fulfill legal requirements. How common are GPS failures? I would imagine that even with a failed GPS, with IFR reserves one could always get to some place where a visual approach is possible? I get the stricter rules in Canada, but 100% of my flying is done along the U.S. border and in the U.S.

Why is there only a requirement for secondary means of nav if using a non-WAAS GPS in the U.S. Is a non-WAAS unit more likely to fail than a WAAS unit?

If two similar units is advisable, I would have to consider spending less on the primary e.g. going with two 430W units or something along those lines, to stay within budget.

 

[Chrisgoesflying]

I was thinking a Garmin 650 as primary and then something cheap as secondary. What about a Garmin 175 as primary and a 400 as secondary? Would those two be worlds apart from a usability standpoint in case of an emergency?

 

[Groundpounder]

I was thinking a Garmin 650 as primary and then something cheap as secondary. What about a Garmin 175 as primary and a 400 as secondary? Would those two be worlds apart from a usability standpoint in case of an emergency?

I would do a gtn650 and a 175. That way they can talk to each other and you don't have to worry about reprogramming the other unit during some sort of failure.

What are you doing for a 2nd com unit? You could always do a nav/com of some sort, that way you have the ability to navigate if the gps network goes down.

 

[Chrisgoesflying]

What are you doing for a 2nd com unit?

I have a SL40 in the plane right now. Was keeping that one as a backup com. GTN650 + 175 might stretch it budget wise.

 

[Groundpounder]

It would be worth the extra money. An old GPS may not have any factory support left, and if it breaks you may end up having to spend even more money to put in the modern unit you should have in the first place

 

[Chrisgoesflying]

It would be worth the extra money. An old GPS may not have any factory support left, and if it breaks you may end up having to spend even more money to put in the modern unit you should have in the first place

I get that. This is why i want the best unit possible as the primary unit. what i’m really trying to figure out is, how necessary are two gps units. if it’s just a Canadian legal requirement due to the large frozen tundra we have further north, i’d rather spend on a nice primary unit and go with the cheapest option for the backup unit to fulfill legal requirements since i never fly over the frozen tundra anyways.

so, you US based pilots with a good waas unit, do you have a backup unit? also, what scenarios would cause one unit to fail but not the other besides malfunctioning of the primary unit? i assume a local gps failure would affect both units, so would an electrical issue on board.

if the general consensus is having two decent gps units is necessary for ifr, i’d have to make concessions for the primary unit. if the general consensus is having one unit is fine, i can get the best unit money can buy for primary and anything cheap that just satisfies regs as secondary.

 

[FORANE]

Been flying with one certified gps for 20 years. I have vor capability as backup but honestly would trust my tablet with avare as backup. I realize that statement will raise concern from some here.

 

[Jim K]

you US based pilots with a good waas unit, do you have a backup unit? also, what scenarios would cause one unit to fail but not the other besides malfunctioning of the primary unit? i assume a local gps failure would affect both units, so would an electrical issue on board.

I have a second nav/com that I consider the backup to my GTN. Also allows me to easily complete my nav checks. If the regs allow it, that would be the cheapest option. The chance of a gps outage is slim, but dual navs is nice to have if you ever have to rely on them, as well as in training.

Another negative of older gps units is database updates. The kln94 is a pain to update and the database subscription is expensive. An older Garmin could at least have a bundled database subscription, but you still are dealing with proprietary data cards and readers. Garmin's database concierge spoils you pretty fast.

 

[Chrisgoesflying]

I have a second nav/com that I consider the backup to my GTN.

So that would be VOR navigation? I did consider this as a "backup" especially since I already have all of those on the plane, VOR, DME and they're working. Having said that, I don't know if they would be "legal" as a backup. My CFI said that this equipment would get me into only 1 airport within 200 nm of our home airport and even there, the VOR transmitter will be shut down the next time it breaks.

 

[Jim K]

So that would be VOR navigation? I did consider this as a "backup" especially since I already have all of those on the plane, VOR, DME and they're working. Having said that, I don't know if they would be "legal" as a backup. My CFI said that this equipment would get me into only 1 airport within 200 nm of our home airport and even there, the VOR transmitter will be shut down the next time it breaks.

Correct. I was unsure about what Canada is going to do with VOR's. In the US the plan is to retain a "minimum operational network" of VOR's to allow navigation in a gps outage. My home airport has a VOR that is supposed to be retained and several VOR approaches.

A nav receiver with a glideslope indicator gets you ILS as well, which might be the only way to get down on an Imc day if gps is out. I would be surprised if there's only one ILS within 200 miles of you, but I guess America's hat might be more desolate than I realized

 

[Chrisgoesflying]

I would be surprised if there's only one ILS within 200 miles of you

I have not fact checked my CFI but last time I wanted to do some simulated instrument training, I suggested to do some practice approaches. He said, sorry can't do with your equipment. He said we'd need a GPS. I asked what happened to my good ol' 1960s technology and he said all the airports in the area no longer support those. Maybe the very large international airports still do but we couldn't go there for practice purposes as landing there would cost $1,000+ lol. So, maybe still legal as in they would let me get down in an emergency but not very practical. Having said that, if this is indeed legal as per the regs, that would be the cheapest option and I can splurge on my one and primary GPS unit.

 

[Llewtrah381]

honestly would trust my tablet with avare as backup. I realize that statement will raise concern from some here.

I’m with you 100%. One time I shot three of the same approach, first with the certified GPS, the second with the $130 Samsung tablet and Avare, and the third with the Area 660 (had a safety pilot for this). Totally doable the last two ways

 

[murphey]

There are 2 possible failures - the first, GPS system fail means it doesn't matter is you have another GPS unit (certified or tablet), nothing will work. The second is a failure of the unit itself, which is possible but very rare. I'd go with a garmin 175 as the backup, and the 650 as the primary. Make sure you have a CDI that works with both or 2 CDIs, each connected to a unit and isolated from the other unit.

 

[asicer]

GTN650 + INS429 is probably the most cost effective way of fulfilling the requirement and still have a complete panel. I don't know how Canada feels about non-TSO equipment, though (USA is OK with it as long as the installer is OK with it).

 

[midlifeflyer]

Why is there only a requirement for secondary means of nav if using a non-WAAS GPS in the U.S. Is a non-WAAS unit more likely to fail than a WAAS unit

At least that’s the theory. Not just failure but overall reliability. WAAS doesn’t just give you vertical glidepath capability. Obviously there’s more to it, but the first sentence of the AIM discussion of WAAS pretty much gives the essence.

The FAA developed the WAAS to improve the accuracy, integrity and availability of GPS signals.​

 

[guest user]

I think the question has two answers:

1) To be legal, you can just keep the VORs as your backup and you're legal. After all, they should suffice to get your where you're going. 200nm might be a restriction based on fuel, but not the instruments.
2) To be compliant w/ the intent, you're going to be wanting the double GPS units. The failure is almost guaranteed to happen at a bad time. There is the argument for making them the same make / model so to reduce the stress of having to switch to the secondary GPS unit. My thought would be to get at least a different model, if not entirely different to make/model. The reason is simply that a software bug is not out of the question. If they're the same units, you're going to hit the same bug in each case. Not really likely, but then if this was about likely, we would just go w/ option 1 and call it good.

 

[Jim K]

I have not fact checked my CFI but last time I wanted to do some simulated instrument training, I suggested to do some practice approaches. He said, sorry can't do with your equipment. He said we'd need a GPS. I asked what happened to my good ol' 1960s technology and he said all the airports in the area no longer support those. Maybe the very large international airports still do but we couldn't go there for practice purposes as landing there would cost $1,000+ lol. So, maybe still legal as in they would let me get down in an emergency but not very practical. Having said that, if this is indeed legal as per the regs, that would be the cheapest option and I can splurge on my one and primary GPS unit.

I would suggest opening your efb and looking at the approaches at every airport within 150 miles of your base. See how many ils approaches there are. Id love to do it for you, but I'm too cheap and only buy the US charts. I will say that nav radios are still very useful in the US, and I know you fly down here a lot. I've probably got a dozen ILS approaches within 40 miles of me, half of which are at uncontrolled fields.

 

[Chrisgoesflying]

I would suggest opening your efb and looking at the approaches at every airport within 150 miles of your base. See how many ils approaches there are. Id love to do it for you, but I'm too cheap and only buy the US charts. I will say that nav radios are still very useful in the US, and I know you fly down here a lot. I've probably got a dozen ILS approaches within 40 miles of me, half of which are at uncontrolled fields.

I counted 3. One is at an airport that doesn’t allow training and if I go there, even for a missed approach, they’ll send me a $1,000 bill. That one is the nearest. The other two are ~100 miles away. One of them also has landing fees, about $25 per landing including training. The third one, same distance and no charge there but they only have one ILS approach so if the wind is coming from the wrong direction, you’d land with a tailwind.

 

[Ed Haywood]

There are 2 possible failures - the first, GPS system fail means it doesn't matter is you have another GPS unit (certified or tablet), nothing will work. The second is a failure of the unit itself, which is possible but very rare. I'd go with a garmin 175 as the backup, and the 650 as the primary. Make sure you have a CDI that works with both or 2 CDIs, each connected to a unit and isolated from the other unit.

GPS system failure is wildly unlikely. There is a massive amount of redundancy built in. The only plausible scenario for a wide area outage would be space-based kinetic weapons attack to physically destroy multiple satellites, ie. an act of war.

Unit failure is far more common. One sloppy crimp in a harness is all it takes.

 

[guest user]

GPS system failure is wildly unlikely. There is a massive amount of redundancy built in. The only plausible scenario for a wide area outage would be space-based kinetic weapons attack to physically destroy multiple satellites, ie. an act of war.

Unit failure is far more common. One sloppy crimp in a harness is all it takes.

I seem to remember a case happening to a user here on POA w/in the last year or so. This would have been a localized outage, but it is not impossible to run into a GPS dead zone.

 

[chemgeek]

For IFR a second COM unit is in my essential bucket. Backup COM is your lifeline if a nav box crumps. Two GPS units is nice, especially if they can cross feed, but I would want at least one unit to have VOR/LOC/ILS capability. A GPS/NAV/COM + GPS COM or a GPS/NAV/COM + NAV/COM would by my choices. In my plane I have option #2 so I always have COM/VOR/LOC/ILS no matter which unit fails.