Long flight Autopilot issue

[fppilot]

I've detailed an issue I am experiencing with the autopilot on longer flights in the previous UP DN buttons topic here in the Redux support forum, and also in PM exchanges here. Experienced the issue again today' so time to bring up here to see if other users are experiencing the same. On flights usually of over two hours duration when on cruise in NAV mode, the KAP 140, on its own, switches from NAV mode to either ROL or HDG.

Other users, please before bombarding me with questions and theories, let me say that for the past several flights I have observed the situation very carefully. The issue is not occurring at turns in the flight plan, and then obviously it is not an issue of steep turns. It is not being caused by user inputs as I have kept hands off and merely watched. In most cases it is such a subtle occurrence that it is difficult to see it occur. Just one minute I am cruising along in NAV mode, and I look down a few seconds later and find it in ROL or HDG mode. So I have a request of other users, and a suggestion to the developers.

I am flying with a pair of RXP GNS GPS gauges, a 530v2 and a 430v2. So to attempt to isolate the issue I must consider both the Redux and the GPS gauges. Are any of you flying this model with RXP GNS gauges? If so, have you flown AP assisted flights of two hours duration or more?

Then the suggestion. I have a friend who IRL flies a 310, and I have flown with him on several occasions, but not in the last year or so. I spoke with him today and he has not had that experience IRL. One question he had is if the AP sounds any alert when it switches. My answer is no. He was quite surprised by my answer. Especially so in the case where the AP switches to ROL. So my suggestion is to sense or trap when these changes occur and signal an audio alert. Is that possible?

[Krazycolin]

It's possible if the real thing does so... Does it? (Tomas?)

[bpieke]

When this happens, are your fuel tanks in balance?

[fppilot]

When this happens, are your fuel tanks in balance?

Yes. And I tested if switching tanks was a trigger. Result was no.

[fppilot]

It's possible if the real thing does so... Does it? (Tomas?)

I have a friend who IRL flies a 310, and I have flown with him on several occasions, but not in the last year or so. I spoke with him today and he has not had that experience IRL.

How closely did you read my post?

[Krazycolin]

I did read it. Hence the question to Tomas.

Your friend might be surprised but, if the real thing doesn't ding.. then ours won't either.

[Taguilo]

Frank,

The problem that you are reporting is related to a loss of GPS valid signal. That might be caused by a scenery issue or RXP bug.
In our KAP, different from other autopilots, we not only check for a GPS signal present, but also that it is valid.
When the KAP detects that it has become invalid, it reverts to previous roll mode, either ROL or HDG.
There is no alert sound as reversion is a valid procedure. However, I will add an audible tone if that might help to note when it happens.

Expect an update with the next build.

Tomas

[fppilot]

Frank,

The problem that you are reporting is related to a loss of GPS valid signal. That might be caused by a scenery issue or RXP bug.
In our KAP, different from other autopilots, we not only check for a GPS signal present, but also that it is valid.
When the KAP detects that it has become invalid, it reverts to previous roll mode, either ROL or HDG.
There is no alert sound as reversion is a valid procedure. However, I will add an audible tone if that might help to note when it happens.

Expect an update with the next build.

Tomas

Tomas,
Is there a way to create a timing loop or delay loop for the detection of or trap of signal loss? I understand the drive to be real world accurate in the functions, but this is a simulator and there are influences from the simulator that do not exist in the real world. Scenery loads, weather refresh, even ATC.

Also, it seems pertinent to point out here that all of the events appear to happen at very close to two-hour increments and I know of no simulator or GPS event that is so consistent. I had this happen twice yesterday during a 4.5 hour flight. Once at just before 2 hours based on the nice timer in the Redux's transponder, the other time at close to the 4 hour mark. The timing may be closer to from when the aircraft is either started from cold and dark, or loaded as running. Yesterday the first time the AP switched from NAV to HDG, the second time it switched from NAV to ROL. So the operation when this happens is not always the same.

I do not have the F1 GNS so I cannot check RXP vs F1 on this issue. That is expressly why I started this topic. To determine if any other users employ the RXP v2 in the Redux, and their experience.

I have another long flight set up for the day after tomorrow and I will use an RXP GTN 750 in that flight.

Frank

[fppilot]

I have now also inquired of RXP concerning this issue.

[bpieke]

I just flew a test flight.. Sedona to Corvallis Oregon..

Flight1 GTN 750 flight plan, autopilot NAV all the way, 4 hrs + no autopilot issues enroute..

However, I flew the main tanks dry without a single warning.. switched to aux tanks when
the engines stopped, and flew on until the aux tanks were down to a gallon and a half..

I am surprised.. what are the warning lights in the panel for..

..and are they operational??

[N4GIX]

Bert, the "Low Fuel" indicators should illuminate whenever the main (tip) tank fuel level(s) fall below 10 gallons.

[fppilot]

I just flew a test flight.. Sedona to Corvallis Oregon..

Flight1 GTN 750 flight plan, autopilot NAV all the way, 4 hrs + no autopilot issues enroute..

However, I flew the main tanks dry without a single warning.. switched to aux tanks when
the engines stopped, and flew on until the aux tanks were down to a gallon and a half..

I am surprised.. what are the warning lights in the panel for..

..and are they operational??

Good catch. I completed a long flight yesterday from Bloomington, Indiana, to Austin, Tx. Flight time 5.2 hours. Used the RXP GTN 750/650 combination along with the Weather Radar. I also in this case had no autopilot issues. I routinely burn mains down to around 25% of their capacity, switch to aux tanks, burn them down to 25% of their capacity, then back to mains. I was cruising at 12,000 burning just under 70 lbs/hr (per engine) and had almost an hour's fuel in reserve upon landing. So I have not tested the warning system.

The issues I have with the autopilot all come when I use a GNS 530/430 combination, and the timing of the issue has been consistent.

[Stew]

I just flew a test flight.. Sedona to Corvallis Oregon..

Flight1 GTN 750 flight plan, autopilot NAV all the way, 4 hrs + no autopilot issues enroute..

However, I flew the main tanks dry without a single warning.. switched to aux tanks when
the engines stopped, and flew on until the aux tanks were down to a gallon and a half..

I am surprised.. what are the warning lights in the panel for..

..and are they operational??

I thought the proper procedure was to use the aux tanks first, then switch to the mains. If it makes no difference, that's ok, too.

[Stew]

Good catch. I completed a long flight yesterday from Bloomington, Indiana, to Austin, Tx. Flight time 5.2 hours. Used the RXP GTN 750/650 combination along with the Weather Radar. I also in this case had no autopilot issues. I routinely burn mains down to around 25% of their capacity, switch to aux tanks, burn them down to 25% of their capacity, then back to mains. I was cruising at 12,000 burning just under 70 lbs/hr (per engine) and had almost an hour's fuel in reserve upon landing. So I have not tested the warning system.

The issues I have with the autopilot all come when I use a GNS 530/430 combination, and the timing of the issue has been consistent.

It sure sounds like to me the problem is with the GNS 530/430, doesn't it?

[bpieke]

Bert, the "Low Fuel" indicators should illuminate whenever the main (tip) tank fuel level(s) fall below 10 gallons.

Edit.... I just tested and they DO work.. indeed.

Thanks!