G'day Bob, I am trying to get my head around the references for using a TSO-C145A/146A GNSS GPS in Aus.

1. Firstly, to navigate IFR one of the methods is listed in ENR 1.1 para 19.1.1 sub para C, stating "use of a radio navigation system or systems". Does the use of a TSO-C146a come under this wording of 'systems', as it is not a radio nav aid and as such is able to be used under this reference? In other words, what is the reference that allows you to use a GNSS for IFR nav requirements? Or is a TSO-C146a GPS a 'approved self-contained navigation system' as per the above paragraph?

2. Secondly, ENR 1.1 58.3 states for RPT and charter you need 'two in the air and one one the ground' for Radio Nav Aid alternate planning, and 'one in the air and one on the ground for Air work'. I am trying to find the best reference that states that you can indeed count your TSO-C146a GNSS towards this 'one or two aids' required depending on your category of operations? I have read in CAAP 179-1(1) dated 14 March 2006 on page 35 that 'with the contingency capability provided by an FDE capable TSO-C146a receiver and a prediction that FDE will be available during the approach, it is possible to treat GNSS much as you would the ADF or VOR'. Para 8.2 of the same CAAP supports this statement but does not clear up the interaction for operation requirements for multiple nav aids.

3. GEN 1.5 para 2.1 states the min serviceable nav aids required to be fitted to an acft for IFR flight navigation per operation category, which for me as an Airwork category pilot is one.

4. GEN 1.5 para 2.1 doesn't remove the requirement for nav aid requirements for alternates as per ENR 1.1 58.3 or does it?

5. Additionally GEN 1.5 Para 8.5.5.3 states that a TSO-C146a and valid FDE prediction can be used towards to satisfy ENR 1.1 para 58.3 and ENR 1.10 para 1.5.1? Is this the answer to my first second paragraph? i.e., Can a TSO-C146a with valid FDE be used towards the number of aids you need? If so, what's the reference?

6. An example may help me out. Let's say I am now a Charter category and am going to a destination that only has a GNSS approach. I have one TSO-C146a GNSS and a valid FDE for my destination, and there are no other alt requirements for weather or lighting? As I can only use one type of approach I think I would need an alternate, as I only have 'one in the air and one on the ground'. If I was Airwork category I would not need an alt for nav aids. Is my thinking correct or does a TSO-C146a GNSS allow me to use it for 'sole means' navigation.

I know I have asked a few questions here but I am trying to nut out the references once and for all.

Thanks again, please let me know if I haven't made myself clear, there is a good possibility I have confused everyone.

Cheers,

Andrew

Gidday Andrew,

Sorry for the delay in answering you, I've been a bit busy lately...

Actually this is an area that has caused some debate among some of the very experienced IFR instructors I know. Most wish that CASA would rewrite the whole of AIP 1.1.58. When it comes to nav aid requirements for alternate planning there is no specific mention of GPS except to say that a TSO 129 GPS does not satisfy the requirements for alternate planning. However it doesn't say that a TSO 145/6 GPS alone would satisfy the requirement. As far as I can see, the requirement for CHTR and RPT to have two separate approaches available or to have two airborne aids capable of an approach published for a ground-based aid still applies. I sum it up as follows....

A 145/6 GPS or 129 GPS is considered to be a system and therefore qualifies as a sole means en route navigation aid. See AIP GEN 1.5 para 8.5.5.1b.

As far as navigation is concerned, you only need one such GPS providing you have FDE and no warnings are current.

As far as flying an approach is concerned, you can do an RNAV GNSS approach at an aerodrome that has only an RNAV GNSS approach available providing you use a 145/6 GPS. Note the distinction between 145/6 and 129 GPS is not based on the accuracy of the aid, it is based on the reliability [integrity] of the system. You can fly an RNAV/GNSS approach perfectly well on either, but if you use a 129, you must have another 'conventional' approach available in case it fails. However you can trust a 145/6 GPS even when it is the only approach available. In other words, a 145/6 GPS has the same 'status' as an NDB or VOR.

As far as alternate planning is concerned, even though you can assume the 145/6 GPS will be available for an approach, if you are CHTR or RPT, you still need a second approach based on a ground-based aid [ADF or VOR], to satisfy the requirements of AIP ENR 1.1 para 58.3. So a PVT IFR flight with a 145/6 GPS could avoid the alternate requirement if the only approach available was an RNAV/GNSS approach, however a CHTR or RPT IFR flight would still require an alternate unless an approach based on a ground-based aid was also available.

If you only have a TSO 129, you must cross it off the list as far as alternate planning is concerned, although it still meets the requirements for navigation [and approach providing an alternate approach is also available] .

Hi Bob, thanks for your reply.

Do you know what the difference is between a TSO-C145/6 Vs a TSO-C145a/6a is? I am unsure of what the little 'a' indicates?

I've been told it stands for 'amended'. It has no operational significance.

Thanks again Bob, have a good one!

Hi Bob, me again.

I am not sure of the latest version of AIP has changed the requirements for using a TSO 129 GPS for alt planning. AIP GEN dated 15 Nov 12 states in para 8.5.5.3 that a RNAV NPA129, 145 and 146 can be used to satisfy the requirements of ENR 1.1 para 58.3. The change bar highlights that this now includes TSO 129 GPS's, whereas before this was not so.

This appears to conflict with the info two pages over in the table 8.5.5.4 RNAV NPA note 3 and 4.

Again, I agree with you that this section needs to be re-written. Amongst my MECIR IFR peers there is a lot on debate as to whether you can use a TSO 145/6 GPS to count towards the number of aids you need for alt planning. I think you can, but am now unsure as to that these changes mean for a 129 GPS.

If you could help out with my understanding it would be very much appreciated.

Cheers again,

Andrew

Andrew

I have again contacted CASA on this issue. My e-mail has been forwarded on to CASA's standards division. The reply I got left me more confused than ever. I feel confident though that, if you got a question on this topic in the CASA IREX exam, you would be correct if you said that a 129 cannot be used to satisfy the alternate requirement. If I get a more satisfactory reply I will certainly let you know.

Bob

G'day Bob, thanks for sending off an email to CASA. I would be very interested in seeing there response.

Your book cover's the issue nicely, the rules just appear to ave changed slightly.

Thanks again for your help,

Andrew

Hi Guys,

I'm currently studying for my IREX that i'm sitting tomorrow. I too keep getting hung up on the GNSS requirements for IFR flight and Charter. I'd like to get a second opinion on my interpretation of things below:
1) AIP GEN 1.5 para 2.1 , (in my case Jepp ATC AU 509) gives you the requirements for en-route tracking in which TSO 129 is permitted.
2) AIP ENR 1.1 para 58.3 (in my case Jepp ATC 304) give you the alternate requirements for an aerodrome but doesn't specify what TSO's are acceptable
3) Additional Specifications for GPS required for IFR charter aircraft are outlined in CAO 20.18 Section 9D.??? unsure of the relevance of this. but basically any GPS put in a charter aircraft after feb 2014 is only allowed to be TSO 145 or better
4) AIP GEN 1.5 page 21 (para 8.5.5.4 ) Specifies that TSO 129 is not alternate suitable

from this i would assume that if you're flying to a destination, hypothetically with only an RNAV approach (eg Tumut) and you do not wish to carry an alternate, and you're Charter IFR. you must be equipped with 2 x TSO 145 or higher receivers in the aircraft

problems is i can't find the equivalent reference for the Jepps...
The more I research this the more confused I become...

Can i get your opinions?

Hello Bob,

I recently came across 'Performance Based Navigation' AIC (H05/18 - Effective 201802010300 UTC) that applies to this thread (regarding alternate planning requirements when using GNSS).

According to paragraph 10.4, RPT/CHTR operations do not require an alternate if the destination is served by:
- One type of instrument approach procedure (RNAV GNSS or VOR or NDB) and the aircraft is fitted with 2 independent systems (2 x GNSS or 2 x VOR or 2 x ADF); or
- Two different types of instrument approach procedures (RNAV GNSS and VOR or RNAV GNSS and NDB) and the aircraft is fitted with 2 seperate systems (1 x GNSS and 1 x VOR or 1 x GNSS and 1 x ADF).

I have provided the link below for all to read:
www.airservicesaustralia.com/aip/current/sup/a18-h05.pdf

Kind regards,

Ryan T