A couple of IFR GPS questions

[struggler123]

Hi all,

I've only recently completed my MECIR a few months ago an had a couple of questions with regard to IFR gps op's.

Question 1:

Can you use an IFR GPS (tso129 or higher) for dead reckoning navigation above LSALT in either VMC or IMC with an expired database?

I'm asking because in my hand written notes from my MECIR GPS course I've written ''if the database has expired you cannot descend below LSALT, MSA or MDA in IMC'' and ''you can use an expired database above LSALT in IMC or VMC''. Although I'm having trouble finding something concrete in the reg's about the topic to back up these notes I've taken.

All I can find in the reg's is in AIP GEN 1.5 para 8.2.1 '' For RNAV systems that contain an updateable database, that database must be current when the system is used for flights under the IFR/NVFR'' and para 8.3.1 ''Only data from a current validated database may be used for navigation below LSALT/MSA.''

Para 8.2.1 covers RNAV systems but not dead reckoning and para 8.3.1 covers navigation below LSALT but not above.

Also in the table provided on GEN 1.5 -16 ''GNSS applications - IFR'', the section about using GPS as a dead reckoning substitute, nothing is mentioned about database currency.

Also page 26 in CAAP 179A mentions:
The principal requirements relating to GNSS navigation data are:

-GNSS navigation requires a current database appropriate to the operation.

-Only data from a current validated database may be used for navigation below the LSALT or MSA.

I soon hope to be flying single pilot IFR in the top end and I'm aware that many company's IFR twins do have tso 129 gps' installed but don't have current databases.

Question 2:

Scenario:
You are on a RPT or charter flight in a plane with only one ADF and one tso 146a gps with FDE available and were flying to an aerodrome that had a published NDB approach and a published RNAV approach. Assuming there is no need for an alternate due lighting etc. Would this scenario require an alternate aerodrome to be planned for?

My thinking the answer is no alternate needs to be planned for as you can suffer the failure of an airborne aid and still conduct a published approach. Although I am uncertain as I find the reg's with regard to this area unclear.

[Fly-by-Desire]

You are right for question 2, but if it was a 129 you would require an alternate, it needs to be a 146 with FDE. Keep in mind that you can have a 146 and still need an alternate if there is an outage on 146/FDE during your arrival.

I dont know about the expired databases, but i cant imagine it would be allowed.

[Mach E Avelli]

Dead (or ded for deduced) reckoning navigation: I don't see why it matters whether the GPS database is current or not. With DR - whether IFR or VFR - you are presumably outside rated coverage of ground-based navaids. So you should use any means at your disposal to keep your DR updated e.g. a fix on a coastline or island on radar in map mode is better than simply doing nothing for an hour. You may even be able to derive a reasonable groundspeed from radar if you think about it.
So, if you are simply using GPS to measure groundspeed, or getting a lat and long and plotting it to update your DR, what would be the objection? GPS lat and long and speed info is not dependent on currency of the data base. On the other hand if you were using GPS to define waypoints, that would not be legal with an expired database.

[TSIO540]

Re Q1: There is nothing stopping you from using any kind of navigation tool above lowest safe, so long as you are using the correct procedures to fix your position. I.e. Using visual fixes, navaid transition or bearing/distance fixes at intervals not exceeding 2 hours etc

Proof of this, I use a GPS that was last updated in 1994 because it still gives accurate estimates and ground speeds, however it is never sufficient for position fixing in normal operations.

This may not be entirely relevant in the bush but even when you do have RNAV capability and you are on a route with a terrestrial navaid, you must use it.

Re: dead reckoning substitute

Go with Mach E Avelli's correction :ok:

Re Q2: I use the "two up / one down or two down / one up" rule of thumb. I.e. You must have two methods of approach at your final destination.

That can be one terrestrial navaid and two separate receivers, or two terrestrial navaids and one separate receiver for each (ndb and vor), however a TSO145 or TSO146 GPS may be substituted for one of the above aircraft systems or for one navaid if you have a valid RAIM prediction showing availability and fuel to hold if there are any outages forecast.

I understand that it is also possible to use GPS as sole means (i.e. carry no vor or ndb approach capability) if you have two separate TSO146 units and a valid RAIM prediciton.

- This is of course assuming that you will be arriving in the dark or with a forecast showing >SCT below LSALT+500ft and visibility <8000m on the last route segment

[The Green Goblin]

If it is expired you are not GPS RNAV approved and are not able to give position fixes at enroute waypoints unless they are a radio navigation aid. This will cause you planning inflexibility.

There is nothing stopping you from using it to supplement your navigation, but it should not be used to give distance information to other IFR aeroplanes, or to ATC to provide lateral airway separation.

Jepp Radio Aids AU-5

5.2 Database Currency

5.2.1 For RNAV systems that contain an update-able database, that database must be current when the system is used for flights under the IFR/Night VFR (So technically you should not be using it at all)

5.3 Operations Below LSALT/MSA

5.3.1 Only data from a current validated database may be used for navigation below the LSALT/MSA. Manually entered data must not be used for navigation below the LSALTMSA, unless specifically authorized by CASA.