The ILS/ VOR and GPS annunciator

[NOSIGN]

I was caught out the other night becoming established on an ILS by forgetting to switch the gps annunciator switch from GPS enroute mode to NAV mode (light twin). :O

I'm sure many Pilots have done this before and I reckon that eliminating the ILS ident (navaid ident) when the instrument is in GPS mode could help the situation from re-occuring.

What are your thoughts? Is there a good reason why TSO'd gps' allow the navaid ident to be recieved even though you're tracking via GPS CDI (the position of the navaid) rather than the navaid itself?

[Capt Pit Bull]

Because you want to be able to identify it before you start using it?

pb

[SNS3Guppy]

Originaly part of the installation requirement with GPS was that the GPS would automatically get kicked off if an ILS frequency was selected. One would have to be careful selecting nav frequencies on the VHF to avoid disconnecting the GPS.

Part of your verification when flying the ILS, however,is that not only are you tuning to and listening to the ILS, but that you've got your cockpit set up to fly it...which includes verifying the source of your nav signal to cockpit instrumentation.

[NOSIGN]

Captn Pit Bull,

perhaps you misinterpretted my post; sure you need to identify the aid when you're using it but when you're tracking to an aid via the GPS, you're identification of it is by confirming it's lat/ long not its morse ident. If the aid that you're tracking to happens to be a VOR or ILS/ LLZ, by selecting the ident function on the navaid (if you also have it tuned) the panel will annunciate the morse code of the station even though you're tracking via a precision approach say (error scale has been decreased). I argue that this can cause confusion, entertaining the thought (if your not thinking clearly) that you have switched off enroute mode and selected NAV mode. The assumption here is that the GPS does not have precision approach guidance, e.g. Garmin 155 TSO or similar.

SNS3Guppy,

that's interesting. I think I would prefer if the GPS was given the boot and auto changed to NAV when an ILS frequency was selected... AS LONG AS THERE WAS A BIG BRIGHT LAMP FLASHING TO ALERT ME TO THE FACT! :}

Was this requirement waived in the early GPS systems?

On this particular night I stuffed up my verification of the source of the aid but I will be more cautious next time :E

[411A]

What are your thoughts? Is there a good reason why TSO'd gps' allow the navaid ident to be recieved even though you're tracking via GPS CDI (the position of the navaid) rather than the navaid itself?

The GPS receiver has nothing to do this, as it just sits there providing a signal that then is enunciated elsewhere.
Rather, it is the signal priority switching of the particular avionics installation the comes into the picture.

For example, long before GPS was available to civil aircraft users, what normally was used was triple INS, supplied to an FMS unit(s)

The Lockheed TriStar was the first to have this equipment (circa 1976 or thereabouts), and of course the area nav system from the FMS (RNAV) was normally used for enroute (and sometimes, terminal) navigation.
However, when an ILS approach was to be used, switching was done automatically...IE: if the pilot failed to switch manually from RNAV data to ILS nav data, when the ILS frequency was tuned and identified, the nav switching was done automatically on the respective display.

Fail/operational, a TriStar exclusive, at the time.

[pistinaround]

I must abmit its happened to me a few years back the company I worked for did not install a green light and a blue light on the instrument panel for the selection. At the time it seemed like a small issue but looking back could have been quite a different story , lucky I was visual for most of the approach but thinking back on it that night It thought it could have turned out much worse. Reason being I was tracking in via the GPS enroute then started the approach lucky for me it was an ILS and I changed my intrest to the VOR/DME. learnt a lesson from that.

[NOSIGN]

411A,

Obviously Pilot's have advanced with time and I have been left behind :}

Next opportunity; i'll read up on if "priority switching" is installed (but not used) on the radio's that i'm using.

I think that the TriStar had the the right idea, further, that a TSO'd avionics installation (or even RNAV only installation) should have a priority switching circuit - especially important if you have only one NAV display.

Thanks for the informative reply.

[Capt Pit Bull]

perhaps you misinterpretted my post; sure you need to identify the aid when you're using it but when you're tracking to an aid via the GPS, you're identification of it is by confirming it's lat/ long not its morse ident.

I don't think I misinterpreted you.

When you're tracking to an RNAV waypoint, sure, its just a point in space. The fact that it's in the same place as a terrestrial navaid is coincidental. The issue is what happens when you reach that point, and the next track of your flight is predicated upon a conventional Navaid. e.g. an ILS.

You always want to be one step ahead of the game, so whilst you are still navigating by GPS you'll want to tune and ident the ILS. Otherwise, when you reach the final waypoint and you're just swinging in the breeze from a navigation point of view. Not the time to find out you misread the freq, or its out of service etc etc.

Additionally, how would you maintain conventional navigation cross checks when in the en route phase using the GPS, if you can't identify an aid?

Look, you made a switchery screw up, and as you said be more cautious next time.

pb

[Graybeard]

Sorry, 411A, the KSSU (KLM, SAS, SR, UTA+) version of the DC10-30 had the AINS-70, Area Inertial Navigation System, beginning in 1973. It would fly a complete trip, including tuning the ILS receivers for the approach. It had over 13,000 waypoints and company routes in its internal database. About all the pilot had to do was select route, SID and STAR.

It also had a NAV/ILS switch on the glareshield, mode annunciator in the HSI, etc.

GB

[NOSIGN]

Mode annunciator in the HSI - that would work nicely. 1973? I need to upgrade!

[ahramin]

On modern HSIs, the mode annunciator is on the HSI screen. Having it on a remote annunciator panel is just a compromise solution for steam gauge HSIs.

Fortunately the requirement to force NAV mode when an ILS frequency is tuned has been removed. There are still many aircraft wired this way and I have flown a few. It is quite annoying not being able to preselect the ILS.

No ident would be the same problem. When using RNAV to get to the LOC, you should have everything set up long before you get there, including identifying the ILS.

If you don't plan on ever getting into modern avionics though, perhaps you should look into rewiring your system to the old way.

[MU3001A]

I was caught out the other night becoming established on an ILS by forgetting to switch the gps annunciator switch from GPS enroute mode to NAV mode (light twin). http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/embarass.gif


Been there, done that. It's definitely a trap for the unwary when flying an older aircraft equipped with NAV radios that are incompatible with a GPS installation. I don't know that there is a technical fix, other than upgrading to NAV radios that are capable of being wired to switch automaticaly when a LOC frequency is selected. Best advice, when you hear "cleared for the approach" make a conscious effort to check that the NAV/GPS sw is selected for the approach you intend to make.

[SNS3Guppy]

I think I would prefer if the GPS was given the boot and auto changed to NAV when an ILS frequency was selected... AS LONG AS THERE WAS A BIG BRIGHT LAMP FLASHING TO ALERT ME TO THE FACT!

Was this requirement waived in the early GPS systems?


Cockpit annunciation was a required part of the installation for IFR certification, and was very much a requirement for early GPS. Bear in mind that early GPS were enroute and terminal only, with VHF or other navigation required for approach.

Integration with FMS in which the user doesn't discriminate between inputs (but allows the box to do this) have largely done away with some of the more cumbersome procedures that were formerly part of flying an RNAV or GPS approach. With most current units, there's no need to manually sequence waypoints, or veryify each waypoint outside of the database date, etc.

Some systems allow nearly everything to be selected through the FMS (or comparable unit) while others still require manual selection/deselection and tuning. Knowing your specific installation is always critical to safety.

Switching errors have always been a concern, and may always be a concern. Add this to one more good reason to follow a detailed checklist. You're not the only one to inadvertantly follow the wrong signal. I've done it too...I even did it during a sim ride during an interview once...tuned the VOR instead of the ILS...and then even tried to follow it. Very embarassing...but fortunately in the safety of a sim. Mistakes happen. Just make sure that the lessons that come with them are survivable, and stick.

Get to know your radios and annunciation, and develop a technique for verifying what's in use on every approach. Back up your approaches with GPS/FMS, and always verify that what you're seeing is what you should be seeing. Tuning and identifying isn't just listening to the morse, but verifying that everything in the cockpit is set up properly, and configured for the procedure in use.

[411A]

Sorry, 411A, the KSSU (KLM, SAS, SR, UTA+) version of the DC10-30 had the AINS-70, Area Inertial Navigation System, beginning in 1973.

Could be true, except...the TriStar FMS units also included complete engine thrust management, in the mix.
A superb fit....and an electronic moving map display, for good measure, on SaudiArabian L1011 aircraft only.