Equipment required to fly the NDB NDB A approach into CYYF

[eh3fifty]

Dammit! I wrote out replies and AvCanada logged me out and everything is now gone. Time to write again.

Photofly

Your quote from C129 doesn't conflict with my quote from C129. Mine specifically states that when an approach is loaded, the GPS must.....

Yours doesn't say specifics with regard to an approach being loaded or not. They don't conflict.

Nowhere does it say you can't have the GPS go into terminal mode without an approach loaded...

You cannot arm an approach that is not loaded! So no, the terminal mode cannot be forced on the KLN if there is no approach loaded. If there is an approach in the active flight plan then I think you can manually activate up to 50 nm from the airport but I can't confirm that distance.

AuxBatOn

Dunno where you get that info. GPS signals are very accurate and precise.

P.S. TSO C129 doesn't exist anymore.

I'll reply to the rest of the posts later. Gotta go.

[AuxBatOn]

eh3fifty,

Read on GPS theory and how SV positionning can have an effect on how precise your calculated position is when the constellation you see is all bunched up together. Hint: it is not. More so in the vertical but it certainly has an effect on your horizontal position again.

But my point is that RAIM may be a hold up from a time when there weren't 32 SVs in space and oir confidence in the technology was low, which is not the case anymore.

[photofly]

But my point is that RAIM may be a hold up from a time when there weren't 32 SVs in space and oir confidence in the technology was low, which is not the case anymore.

Check the FAA RAIM website. There are still chunks of time when you can't have approach-level RAIM in parts of North America. Especially without baro-aiding. That means chunks of time when you can't do an RNAV approach without WAAS. RAIM isn't a holdover, it's very relevant for those of us still using TSO-C129a compliant receivers. (And no, that document hasn't gone away.)

Here is an aggregate of areas where there was an approach RAIM outage in the marked period:

Screen Shot 2015-02-08 at 9.39.28 PM.png (60.19 KiB) Viewed 1190 times

[AuxBatOn]

Again, what is the concrete effect on the level of precision of your nav equipment. Is that standard antiquated versus what we know of GPS now? I think it is.

It's great to say that an area won't have "approach level RAIM", but what does it exactly and concretely mean.

[photofly]

If the receiver can't verify approach RAIM is available it flags "APPROACH RAIM UNAVAILABLE" and won't load the approach. When I say you cannot fly the approach - I'm being accurate: you can't. That's a concrete certification requirement of any unit certified to meet TSO-C129a. WAAS-capable receivers are different.

[AuxBatOn]

What is the exact effect on the precision of the GPS solution calulated by your receiver? How would it compare to other types of non-precision approach? How would it compare to the TERPs standards applied to RNAV approaches?

I get it, according to TSO-129 you can't. But I believe (and many people do!) that this standard is very antiquated and could be loosened up a bit. Like I said, I can drop a GPS-guided bomb without even considering RAIM.

[photofly]

RAIM is integrity monitoring, not accuracy. The required accuracy can still be obtained, but it can't be verified as correct. (The receiver eliminates each SV in turn and recalculates the solution: RAIM is assured if each such calculation lies sufficiently close to the others. A RAIM calculation therefore requires more SVs in view than are required to calculate a solution - if there aren't enough you can still have a solution but not be able to perform integrity monitoring.)

The problem it seeks to solve is a rogue SV which hasn't been taken off line; rogue enough to give you a false position. RAIM will allow the receiver to eliminate the incorrect data in sufficient time not to fly you into a mountain.

WAAS gets around the problem because satellite integrity data is broadcast over the WAAS channel, alerting the WAAS-capable receiver to ignore the rogue SV.

As I understand it.

So it's not really about "getting more confidence" in GPS. It's a method to very quickly detect and mitigate satellite faults.

I guess what we're interested in is how often do satellites transmit faulty data, and how long does it take for the satellite to be taken offline? Often enough, and long enough, I believe, that RAIM is still required and valuable.

[AuxBatOn]

RAIM is integrity monitoring, not accuracy. The required accuracy can still be obtained, but it can't be verified as correct. (The receiver eliminates each SV in turn and recalculates the solution: RAIM is assured if each such calculation lies sufficiently close to the others. A RAIM calculation therefore requires more SVs in view than are required to calculate a solution - if there aren't enough you can still have a solution but not be able to perform integrity monitoring.)

The problem it seeks to solve is a rogue SV which has gone un-announced; rogue enough to give you a false position. RAIM will alert you to that in sufficient time not to fly into a mountain.

WAAS gets around the problem because satellite integrity data is broadcast over the WAAS channel that alerts the WAAS-capable receiver to ignore a rogue SV when calculating a solution.

As I understand it.

So it's not really about "getting more confidence" in GPS. It's a method to detect and mitigate satellite faults.

I know what RAIM is and yes, in the end, it has an effect on you navigation solution.

When RAIM is unavailable, it means there are less than 5 Healthy, well-positionned SV in view. You can get a 2-D solution with 3 SVs... What I am more interested in knowing is the frequency of SV faults detected and the impact of these faults when not excluded. (By SV vaults, I also include atmospheric refraction)

This is where the "confidence" in GPS lies: knowing that faults don't happen regularly and that the impact of such faults is negligeable when compared to the standards of approach design.

A better way of warning you of problems would be to calculate a circular error probable at any given moment and warning you when a certain level of impresision has been achieved for a given phase of flight.

[photofly]

WIth respect, although I have no doubt you understand how RAIM works I think you aren't giving enough import to what it provides.

If you have 4 well positioned SVs in view you may have a very accurate solution. If one of those 4 goes rogue you will still have a very small CEP but the solution will be entirely wrong with no way for you to tell. If it takes 30 seconds for that SV to be taken off line then for 30 seconds your approach may be gravely imperilled.

The requirement for RAIM prevents you from being in a position where that is a possibility: it would not allow you to begin the approach unless 5 SVs are in view. Then if one of them goes rogue then within a very short time you will see a RAIM ERROR and be forced to discontinue the approach. Meanwhile the rogue data is eliminated from your solution. You will never be shown an incorrect position.

This is where the "confidence" in GPS lies: knowing that faults don't happen regularly and that the impact of such faults is negligeable when compared to the standards of approach design.

I would judge that since the system now goes to lengths to broadcast the integrity data via the WAAS channel, the freqency and significance of SV faults is sufficient to cause unacceptable danger to aircraft unable to detect such errors within a very short time, either via RAIM or WAAS.

[AuxBatOn]

If you have 4 well positioned SVs in view you may have a very accurate solution. If one of those 4 goes rogue you will still have a very small CEP but the solution will be entirely wrong with no way to tell.

This doesn't make any sense. If one goes "rogue", your CEP will grow to include your actual position and the position given by the "rogue" SV. In fact, the CEP would most likely be weighted and reduced to CE90 which may exclude the erroneous position. And yes, you could be given a warning if a new standard was developed and introduced into systems.

The other aspect you are missing is how often those SV go "rogue" and what the impact is on your overall solution. I bet it's almost never and negligible. This is the confidence aspect of my argument. And I bet it's comparable to ILS' going off-air while someone is on approach...

It is possible to display position accuracy in-cockpit and give warning when limits are exceeded.

[photofly]

This doesn't make any sense. If one goes "rogue", your CEP will grow to include your actual position and the position given by the "rogue" SV. In fact, the CEP would most likely be weighted and reduced to CE90 which may exclude the erroneous position.

That argument was available to the (smart) people who wrote TSO-C129a, but they insisted on RAIM. I'm sure there was a reason why they felt that CEP wouldn't provide integrity. I don't know what that reason is, but I deduce it's a good reason.

The other aspect you are missing is how often those SV go "rogue" and what the impact is on your overall solution. I bet it's almost never and negligible. This is the confidence aspect of my argument. And I bet it's comparable to ILS' going off-air while someone is on approach...

It likely is just like that. You'll know the self-monitoring requirements get stiffer from Cat I, to Cat II, to Cat III equipment - both the ground equipment and the aircraft equipment.

I'm not missing that aspect - I simply don't have any data from which to form an opinion. The only data point I know is that integrity data is broadcast on WAAS, and therefore still thought to be necessary for safe flight.

[eh3fifty]

AuxBatOn

I appreciate and encourage your enthusiasm to understand this subject matter, however, I think it's apparent that you don't know what RAIM is other than a definition you can read verbatim after searching Google.

The simplest explanation I can give with regard to what RAIM really is would be to compare it to something else. It serves the EXACT same purpose as the red flag on the G/S does on your HSI. It serves the EXACT same purpose as the red flag on your LOC or your VOR, etc.

If you understand that then you must also understand that RAIM will NEVER become obsolete.

As time goes on, we can improve the accuracy of the SVs and improve the overall position solution. For any given level of RNP, that will increase the probability that you will have that RNP at any time. The other consequence is that you will improve the position solution to such a degree that you will be able to fly approaches down to minimums similar to CAT II approaches.

They may change the name from RAIM to something else but what will never change is the requirement to have some way of monitoring and alerting the pilot as to the state of the navigation solution. The only difference between the requirements of GPS and RNP is that RNP requires there to be on-board performance monitoring and alerting. Most GPS units already do this - it's easy to integrate a GPS signal into an RNP solution.

This is where the "confidence" in GPS lies: knowing that faults don't happen regularly and that the impact of such faults is negligeable when compared to the standards of approach design.

I've already explained this but to further clarify - faults rarely happen with ILSs. I've never had an issue with an ILS. Does that mean we should stop monitoring the signals and take out the current systems that are designed to alert ATC when an ILS malfunctions, and also take out the red flag for the LOC and GS?

A better way of warning you of problems would be to calculate a circular error probable at any given moment and warning you when a certain level of impresision has been achieved for a given phase of flight.

The first half of what you said I understood. We already have that! For GPS and RNP. For GPS there are a number of metrics but basically it calculates a circle with a radius that it's 95% confident that your actual position lies within that circle. If that circle radius gets bigger than the particular RAIM level that you require then you'll get a RAIM alert. The same happens for RNP and it's conveniently called ANP (Actual Navigation Performance).

What is the exact effect on the precision of the GPS solution calulated by your receiver?

It doesn't matter. Unless you're involved in improving GPS technology and programing code for GPS satellites, etc, this does not matter! There are many things that affect precision of a GPS solution. If you do a quick search on Google you'll see. You're now trying to calculate how much the position solution moves when you decrease the HDOP by 5%? Is that what you mean by "exact effect" on the solution? I can't help you there. Have you seen the formulas and equations that are used to get a position solution?

Photofly

That website you linked for RAIM prediction... what requirement for flight planning does that satisfy? Isn't that only for the US airspace?

AuxBatOn

Dillution of Precision has far more importance in the precision of your GPS solution yet it is never even mentionned. I doubt many pilots even know about it.

Nothing a pilot ever does will ever change the HDOP or VDOP. It's nice to know but definitely not need to know. Considering the amount of misinformation about GPS with pilots I've flown with, I'd be happy for them to just know the basics about what RAIM is, when it is functioning, what to do when you get a RAIM alert, etc.

BPF

I'm flying the approach off the GPS. The NDB is tuned and is my primary navigation source for an NDB approach with no overlay. Due to all the ADF errors, which you know about, I'm only going to be monitoring the NDB when I'm wings level and in stable flight. If I notice that the GPS CDI is deflected 0.5 miles then I'm focused on re-intercepting and getting my wings level before taking a reading from the NDB. As long as the NDB is within 5 degrees of my inbound course (when the GPS CDI is centred) then I'm happy. If it's not then I'll try to very quickly find out why and if I can't in a short amount of time then I'll do a missed approach. There are an infinite number of situations you can come up with regarding discrepancies between the GPS and NDB. Taking into account all this information and what is legally required, I will try to make a decision that I will be able to defend when seated in the oak chair.

[Big Pistons Forever]

20 Years of ignoring the ADF and trusting the GPS has resulted in the runway showing up exactly where I expected it. The previous 10 years of pre GPS NDB approaches resulted in the runway showing up somewhere ahead but rarely dead ahead, except for the day it decided to point to the thunderstorm 30 miles away instead of the airport.....which really sucked because there was higher ground all around me....

[eh3fifty]

BPF

I fully agree. Fly those approaches on the GPS. That's really the safe way to do it.

But if I can do it safely and legally (monitoring the NDB), why not? Too many pilots get it in their head that they know how things work so they can decide what's safe and fly that instead of following the rules. Once you start disregarding one rule, it can be hard to know what rules you should really be following. This can lead to normalization of deviance. This is an airmanship issue.

Of course you should fly it off the GPS! But have some discipline and follow the rules. The only time you should be breaking the rules is if following the rules will jeopardize safety.

[Big Pistons Forever]

The only time you should be breaking the rules is if following the rules will jeopardize safety.

A agree and the rule that requires 1930 technology to trump 1990's technology is an example where IMO following the rule jeopardizes safety.

If the the ADF needle says I am 10 degrees off track and the GPS needle says I am on track I am not going to go around I am going to continue the approach confident that the aircraft flight path will be aligned with the runway centerline when I break out.

[eh3fifty]

I wanna play Devils advocate here.

When you were flying in the 80's did you tell people that flying an NDB approach with an ADF is unsafe and they shouldn't be doing that? I don't think you did. The minimums and obstacle clearance are built such that you have similar a similar safety level compared to flying an ILS or VOR approach.

Now because a better and more accurate way to fly the approach comes along you say that using the original method is not safe enough? That's a point to discuss, I'm all about improving safety. But how safe do you really need it to be before you will agree to not break rules in the name of safety?

Let's say you now go onto a jet or turboprop in a 705 environment as a pilot. Would you now say that it's too hazardous to fly on the Navajo to Victoria and only fly Jazz or Encore on their Q400?

How much safety is needed to be considered adequate or sufficient?

Step down approaches have been recently deemed "not that safe" and there is a push to always fly constant descent angle approaches. You'll actually get a 2 on your IFR ride now if you can fly a CDA and don't when there is no icing and you aren't circling. Automatic 2. But the key difference here is that it's not illegal to fly a step down approach.

[photofly]

TC AIM COM 3.14.4.1 and 3.14.4.2 give a good overview of the different eras of GPS receiver, TSO-C129a, TSO-C145a/C146a and WAAS-enabled. They answer some of the questions raised in this thread. Probably worth reading by all. (I didn't realize that TSO-C129a receivers still allow for Selective Availability which lowers RAIM availability for them.)

That website you linked for RAIM prediction... what requirement for flight planning does that satisfy?

The one in TC AIM 3.14.5.2.1:
"Pilots using TSO C129/C129a avionics should use the RAIM
prediction feature to ensure that approach-level RAIM will be
supported at the destination or alternate airport for the ETA
(±15 min). This should be done before takeoff..."

(Yes I am aware it says use the RAIM prediction feature of the avionics, but that website is a good start.)

And 3.14.12(c).

Isn't that only for the US airspace?

It covers enough of Ontario to be useful to me. At least it was before they transitioned to using Google Earth plugin, which I can't seem to get to work reliably.

[Big Pistons Forever]

I wanna play Devils advocate here.

When you were flying in the 80's did you tell people that flying an NDB approach with an ADF is unsafe and they shouldn't be doing that? I don't think you did. The minimums and obstacle clearance are built such that you have similar a similar safety level compared to flying an ILS or VOR approach.
.

No because the NDB with all its faults was all we had. The difference is now 20 years later we have a much better solution. It is better in every way, it gives you much more information, not just bearing but distance and groundspeed to a much higher level of reliability and confidence. So why do the rules state to be legal we must use the device that is demonstrably less accurate ? It is obvious that the closer you are to the actual final approach track you are the more margin you have and therefor the safer you will be. 20 years of operating data and we are still having this debate......I just don't get it

[photofly]

My understanding is that there are approaches where, because the position errors that are considered in an overlay approach are different to the errors considered in the traditional navaid approach, an obstacle penetrates the volume that would have to be protected for the overlay to be approved.

You'd have to be pretty unlucky to have a GPS error that would put you in danger on a non-overlay approach, but "pretty unlucky" doesn't cut it with regulators.

It also makes more a little more sense when you consider that approved approaches still have to suit TSO-C129a receivers that date from the SA era when civilian GPS wasn't allowed to be more accurate than 50 metres or so.

[eh3fifty]

Photofly

SA doesn't exist anymore. See COM 3.14.4.1.

Regarding flight planning requirements there are none. The only flight planning RAIM check required is when planning a GPS alternate. Most pilots know there are requirements but I haven't met one that actually knows what exactly needs to be checked. It's all in the AIM COM 3.14 section though.

Edit: I understand that it would be good to have a quick look to see the condition of the satellite constellation before your flight. But there is no requirement to do any sort of pre-flight check of RAIM or satellite constellation.

BPF

We both agree the approach should be flown on the GPS. I just think you should also follow the rules. I fully understand your points about how GPS is more accurate and better. Which is why I totally agree you should use the GPS to fly a non-precision non-overlay approach.

As for why exactly some approaches aren't overlay, I couldn't give you a good answer to that. If you'd like to speak with a guy involved with approach design at TC I can get you contact details.

[photofly]

Photofly

SA doesn't exist anymore. See COM 3.14.4.1.

Indeed. And the US has guaranteed it won't be reintroduced. But since TSO-C129a compliant receivers were designed before that fact, they still have considerably worse RAIM availability than TSO-C145/C146 receivers.

None of which will have affected AuxBaton or his colleagues.

Regarding flight planning requirements there are none.

There appears to be one in TC AIM COM 3.14.5.2.1. I won't quote it again because it doesn't look like you wasted any time reading what I wrote last time I quoted it.

[eh3fifty]

Photofly

I can't say for sure but I'm not sure how having the capability for SA and turning it off affects RAIM availability at all. My understanding is that SA is not controlled by the receiver, a signal is sent from the satellite. So turning SA off improves the accuracy of the signal to the receiver. I don't believe the receiver degrades the signal itself. Plus, it's turned off.

Most likely why 145/146s have better availability is because they generally track 12 satellites vs 8, and have newer software and hardware.

LED tvs have been around for awhile but the newer ones perform better than the older ones. They're still LED tvs.

I read that AIM section and I'm familiar with that recommendation. It is not a requirement. I usually don't bother checking before flight but I will usually check in flight when using a C129 receiver.

[photofly]

Photofly

I can't say for sure but I'm not sure how having the capability for SA and turning it off affects RAIM availability at all. My understanding is that SA is not controlled by the receiver, a signal is sent from the satellite. So turning SA off improves the accuracy of the signal to the receiver. I don't believe the receiver degrades the signal itself. Plus, it's turned off.

Again for someone who recommends everyone else to read sections of the AIM (hilariously, three posts after I mentioned reading the same section), you don't seem to take your own advice.

Here's TC AIM COM 3.14.4

Most first generation avionics do not have FDE and were
designed when GPS had a feature called selective availability
(SA) that deliberately degraded accuracy. SA has since been
discontinued, and new generation WAAS-capable receivers
(TSO C145a/C146a) account for SA being terminated. These
receivers experience a higher RAIM availability, even in the
absence of WAAS messages, and also have FDE capability.

For avionics that cannot take advantage of SA being
discontinued, average RAIM availability is 99.99 percent for
en-route and 99.7 percent for NPA operations for a 24-satellite
GPS constellation. FDE availability ranges from 99.8 percent
for en-route to 89.5 percent for NPA. Avionics that can take
advantage of SA having been discontinued have virtually
100-percent availability of RAIM for en-route and 99.998
percent for NPA; FDE availability ranges from 99.92 percent
for en-route to 99.1 percent for NPA.

[eh3fifty]

Photofly

I could attack you for not reading the very section in the AIM that you chided me for not reading. Do you know the difference between a recommendation and a requirement? Do you know the difference between shall and should?

Stop being a dick.

[photofly]

Thanks for the point out about SA still affecting RAIM for older receivers. I must have missed that.

No problem.

The bit you quote in the AIM about checking RAIM availability before takeoff is strictly a recommendation, not a regulation. "Should", rather than "shall", and all that.

Good catch, yes, agreed.