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GTN FPL Fuel Tested (bug corrected in Landing Fuel on Board)

10 Posts

Several of us have been quite exercised for a long time over the fact that the GTN got its fuel planning quite wrong (in that it always assumed a GC route to destination, rather than on the FPL).

v6.62 came out in June with a fix for this, but I haven’t really been able to test it properly until today,; however, I have now and I can now say that it works beautifully.

It is a shame that Garmin have left this feature (which worked perfectly in the GNS 530) so long, but now we have it, it’s great. The worst shortcoming in the GTN fixed, as far as I am concerned.

(mods, I searched for where this was discussed before, but failed. Please merge as you see fit.)

EGKB Biggin Hill

Not heard of that before. It is absolutely terrible, and makes the Landing Fuel on Board reading pretty well useless.

That it has not been given a wider prominence (since the GTNs came out) tells one something, and you can guess what I think it tells one

Administrator
Shoreham EGKA, United Kingdom

Cool. Thanks for the info.

EKRK, Denmark

Is your gtn wired to take into account fuel totalizer actual readings? Or you have to manually input an estimated average gph?

United Kingdom

Not quite sure what you mean Timothy?
My gtn650 v6.50 gives sensible fuel burns on a route that departs from the destination for each leg and destination….what am I missing?(it’s also connected to fs450 to give destination fuel which more or less agrees)

Last Edited by PeteD at 02 Sep 16:10
EGNS, Other

I wonder if there is more than one way to configure these systems, and some installers do it one way and others do it differently?

In the traditional config, say my Shadin Microflo and a KLN94, the Shadin sends the current FOB (fuel on board) and the current flow rate, to the GPS, which knows the remaining flight plan distance and the current ground speed, and calculates the Landing FOB.

It obviously does it correctly based on the remaining FP distance because if I accidentally end up with a waypoint which doubles back on the same route (but wasn’t immediately spotted because it is perfectly in line with the route), the LFOB suddenly drops alarmingly.

In the above, data flows from the Shadin to the GPS, only.

There is no need for data to flow GPS to Shadin, but you can wire that up on some Shadins, and then (IIRC) you can see the LFOB on the Shadin also.

However none of the above would explain using a great circle route to the destination instead of the flight plan route. That would just be completely dumb. But I can see it could remain undiscovered for years – because most pilots don’t do the longer flights which need fairly delicate fuel management. The vast majority of pilots don’t fly past their bladder endurance so things like this could go undiscovered, especially as to spot it you would also need to have a big detour in the flight plan which you don’t fly.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

There is no need for data to flow GPS to Shadin, but you can wire that up on some Shadins, and then (IIRC) you can see the LFOB on the Shadin also.

I had this done, and was hugely disappointed to see this gives fuel to next waypoint (not to destination), LFOB at next waypoint (not destination), etc. The only real thing gained is nmi/gallon on the Shadin.

ELLX

Don’t know about the Shadin,but there is an option for this in the jpi setup menu for waypoint or destination(didn’t work on the jpi initially and had to be reprogrammed by jpi to work with gtn)

Last Edited by PeteD at 02 Sep 22:22
EGNS, Other

PeteD wrote:

My gtn650 v6.50 gives sensible fuel burns on a route that departs from the destination for each leg and destination….what am I missing?(it’s also connected to fs450 to give destination fuel which more or less agrees)

The total cumulative fuel burn was, until 6.62, calculated on GC. It is now calculated on FPL. If you get a lot of directs, the result will be the much the same, but if you have to fly the route in the FPL it could be, say, 15% different.

This is a bug acknowledged by Garmin and now fixed in 6.62. If it worked for you in 6.50 then that’s the power of magic!

EGKB Biggin Hill

Peter wrote:

makes the Landing Fuel on Board reading pretty well useless.

Yup. But now fixed; a very good reason to upgrade to 6.62.

EGKB Biggin Hill
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