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GTN650/750 track offset function

10 Posts

I realise this is a requirement for a WAAS GPS, but how useful do people here consider it to be in Europe?

Virtually all flight in CAS is done under radar control.

Maybe for flying OCAS?

One hears of airlines doing this over Africa, because of poor ATC services, to prevent head-ons and flying up the back end of the one before you.

Administrator
Shoreham EGKA, United Kingdom

there are areas out there where it seems to be wise flying an off-set of a mile - you mentioned Africa, that's right but also Siberia, Mongolia, China. They often have poor landlines and if they have a flightplan at all they often don't know at which level you approach their area. Therefor they like to have an entry call 10min before you reach the FIR boundary. So the pilot unions once agreed upon flying a mile right of track. But who approached again head-on? The Brits of course as they flew a mile left of track.

EDxx, Germany

Maybe for flying OCAS?

I often fly Biggin -> OCK -> MID/SAM. Unless the weather is terrible (no traffic), I always fly 0.5 miles right of track. You see quite a lot of other traffic on the exact track...

It's also useful when someone asks you to cross an airport to the east/west/north/south rather than overhead - just pop in parallel track and job done. Sure, you could do it visually - but this way the autopilot gets to follow the nice GPSS path.

EGEO

I realise this is a requirement for a WAAS GPS

How would I do that with a GNS430W?

how useful do people here consider it to be in Europe

Probably not useful at all. More useful would be the FMS standard feature to plan vertical paths, you often hear ATC issue something like "descent FL080, pass XYZ VOR not lower than FL120" or "climb FL280 at least FL150 when reaching XYZ". I guess they know that GA aircraft can't do such tricks and don't ask for it.

How would I do that with a GNS430W?

With a flightplan loaded, press menu, scroll to "Parallel Track?", press enter, enter the distance offset in NM (0 to 99), enter, select right or left, enter, press enter to activate.

KUZA, United States

More useful would be the FMS standard feature to plan vertical paths, you often hear ATC issue something like "descent FL080, pass XYZ VOR not lower than FL120" or "climb FL280 at least FL150 when reaching XYZ". I guess they know that GA aircraft can't do such tricks and don't ask for it.

The GTN can do this (they call it VCALC). I have it set up to show me the rate of descent required on the main page once I've told it where I want to be.

I use it all the time - you just dial in the waypoint (usually from the flightplan), distance before/after and desired level and it calculates the vertical speed required. It will also calculate the Top of descent point for a given vertical speed. The only gotcha is that it uses GPS altitudes which can be quite different to flight levels.

EGEO

I use it all the time - you just dial in the waypoint (usually from the flightplan), distance before/after and desired level and it calculates the vertical speed required.

I use the Garmin 496 for that. Set the destination airport as a DCT and you get the VS to target on one (or more) of the screens.

It will also calculate the Top of descent point for a given vertical speed.

I don't think the 496 will do that, but one can get the same result by flying level until the VS to target rises to your desired figure.

The only gotcha is that it uses GPS altitudes which can be quite different to flight levels.

Not different enough though for this purpose. One cannot fly the calculated VS to better than +/-100fpm, and probably +/-200fpm much of the time. The KFC225 VS mode seems to randomly subtract 100fpm...

Administrator
Shoreham EGKA, United Kingdom

I use the Garmin 496 for that. Set the destination airport as a DCT and you get the VS to target on one (or more) of the screens.

It's quite useful to be able to set a certain distance before at which you want to be level.

EGEO

Any panel mount Garmin from the GNS430 onwards (W not required) has had that vertical navigation function (last NAV page for GNS4/530; VCALC for the GTNs), where you can select an altitude (absolute or above ground), a point along the flight planned route including a distance before or after a waypoint, and a desired vertical speed.

It displays a target vertical speed if you were do descend now, and gives a message when reaching the descent point. Also gives a message when approaching the target altitude.

Personally, I prefer to set my FPL page to display the ETE to the waypoints and I work it out in my head, it is quicker [FPL, look, think; not NAV-twiddle-push-push-twiddle-push-push-twiddle-push-push-twiddle-push-push-twiddle...] [or for the GTN users: push-tap-tap-tappeti-tap-tap-tap.. ;-)].

The G1000 allows one to set up the vertical profile for the entire flight plan, and it is even possible to couple that to the autopilot... but don't even try to use that tactically, by the time you have it set up you have probably overshot your destination.

Biggin Hill

In my airline (VS) offsets are mandated in Oceanic and specified on our plog (0-2R). In Africa we offset 2R and make blind calls on 126.9. Everywhere else we can usually offset up to 2R without complaints from ATC.

Offsets to the L are forbidden...

Spending too long online
EGTF Fairoaks, EGLL Heathrow, United Kingdom
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