Garmin 430's

[Keygrip]

I know some smart**** is going to jump up and down about "duplicate postings" - but I've lifted a section of a different thread of mine to post here - to ask for tech info on GPS, not actual usage of GPS.
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I'm curious now about an Arrow I flew recently - had two Garmin 430 GPS's on board. One click of the buttons would give me a page of the SIX nearest VOR's (or whatever) - with frequency, ident, bearing and distance.

None of these were identifiable through morse code idents on the audio panel - you just have to believe them to be accurate. So, if you are going to believe the GPS derived distance, why not believe the GPS derived radial/bearing and accept the information without identing the same stations on the VHF section of the receiver.

If you DO ident the station, through the VHF portion, and the CDI/HSI (whatever) gave you a different reading than the GPS screen, which do you believe?? The digital, accurate, GPS radial/bearing or the not so hot, moving, selectable CDI/OBS indicator on an HSI that doesn't slave 100% accurate with the equally unreliable magnetic compass?

Also wonder about the aerials/antennae on that aircraft. I don't remember seeing a VOR (wire coat hangar style) aerial on the tail - but did see ONE VHF and TWO GPS antennaes on the roof.

Does that suggest that the two VHF (speech) transceivers are fed through a combined antennae, and does that single antennae also get the VOR signal - or do the two standard VOR indicators receive their signals from GPS derived data - in which case GPS actually IS the primary means of navigation - but displayed in a conventional way?
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Also found that whilst flying that Arrow at night - I could not find a way to dim the brightness of the screen(s).......which turned out to be dazzling by the time it got really dark outside.

I'll go ask Piper in a couple of days - but wondered if anybody knew the answer...............how do you dim them?

[The Nr Fairy]

Keygrip:

Re the brightness - check pages 159/160 of the manual, downloadable from Garmin's support pages (http://www.garmin.com/support/userManual.jsp?market=1&subcategory=8&product=010-00139-11) - it should be automatic, but can be manually set through the setup pages.

[swh]

Keygrip,

None of these were identifiable through morse code idents on the audio panel - you just have to believe them to be accurate. So, if you are going to believe the GPS derived distance, why not believe the GPS derived radial/bearing and accept the information without identing the same stations on the VHF section of the receiver.

This would be dependant on your local ICAO state to determine, in Australia you can use the GPS position for the ground based aid for approaches, ie you could use a GPS position for a VOR/DME in lieu for the actual VOR/DME, track via the VOR, but use the GPS for tthe DME portion.

If you DO ident the station, through the VHF portion, and the CDI/HSI (whatever) gave you a different reading than the GPS screen, which do you believe?? The digital, accurate, GPS radial/bearing or the not so hot, moving, selectable CDI/OBS indicator on an HSI that doesn't slave 100% accurate with the equally unreliable magnetic compass?

In Australia when you are in range of ground based aids you should be tracjing via that aid, ie if you are asked to track inbound on the 360 radial reference the VOR it should be via the VOR receiver, not the GPS, as this is the basis for seperation applied, and other aircraft would also have the same errors dispayed in their cockpit.

GPS does not give you slant distrance from the DME, ie at 6000 ft over a DME a DME will indicate close to 1 nm, but a GPS will indicate 0 nm.

Also the VORs magnetic variation is a fixed item that has to be calibrated from time to time, the radial displayed from a GPS is based upon a calculated magnetic variation for that particular position and time in space. Magnetic variation changes with time, position, and altitude, as it is an indocation of the earths mangetic flux

Also wonder about the aerials/antennae on that aircraft. I don't remember seeing a VOR (wire coat hangar style) aerial on the tail - but did see ONE VHF and TWO GPS antennaes on the roof.

Not all VOR antenna are coat hangers, flush mounted, and aerials inside housings are available. Additional aerials would be required for the ILS and transponder also, more than likely on the under side of the aircraft.

SWH