GPSS question

[cliffy]

As one who has no WAAS let alone GPSS a question arises after viewing another thread with a video on a holding pattern entry.

When a holding pattern is entered and held via a GPSS and a GPS sync'd approach plate in view, does the autopilot follow the outline shown on the plate for the holding pattern or does it adjust the outbound leg to allow the 1 min inbound leg to holding as req'd? Or does it always follow the "printed" hold regardless of the inbound leg time?

Never use one so don't know.  

[Marauder]

The GPS knows your ground speed so there is some adjustment to the hold. On a fixed distance hold, it will follow the race track. On a timed hold, it will make adjustments for the timing. I never have flown on a really windy day to see how much adjustment it will do.

One thing is for sure, it is pretty smooth.

[Bob_Belville]

It is pure joy to watch George fly a hold on the GTN750 which superimposes the approach plate over the topography.  

[Danb]

As bob said it is awesome to see what the new avionics including the Gpss and Chris havin done these in nasty windy Wx it's an extra joy watching the machine do properly what I would struggle at. I'm just waiting for the next gen. Where we program our equipment on the ground an do nothing but taxi. Letting the box's do all take off approach and land I assume we will have to use the brakes tho

[ghovey]

They have that airplane already. They call it an f-15.

[Jerry 5TJ]

Even with no autopilot the WAAS GPS will tell you the hold entry type, plot the hold and suggest turn times and headings.   It is possible, I have tried it, to just "drive" around the hold or procedure turn by watching the display.   Since the ground track is displayed (right, Dave?) it is trivial to correct for wind.    I recall, with a shudder, holding using the ADF in ancient times back in the 20th century, but the GPS makes all that pretty darn easy to visualize.

 

We can be "Children of the Magenta" even without auto throttle or n axis autopilots. 

 

 

[flyboy0681]

It is pure joy to watch George fly a hold on the GTN750 which superimposes the approach plate over the topography.  

 

I second the motion. It's very impressive - and smooth.

[rbridges]

Even with no autopilot the WAAS GPS will tell you the hold entry type, plot the hold and suggest turn times and headings.   It is possible, I have tried it, to just "drive" around the hold or procedure turn by watching the display.   Since the ground track is displayed (right, Dave?) it is trivial to correct for wind.    I recall, with a shudder, holding using the ADF in ancient times back in the 20th century, but the GPS makes all that pretty darn easy to visualize.

 

We can be "Children of the Magenta" even without auto throttle or n axis autopilots. 

 

 

During my instrument training, I would time the turns and try to correct for wind knowing that my 430 had a magenta line I could just follow.  oh well, gotta walk before you can run.

[Marauder]

Even with no autopilot the WAAS GPS will tell you the hold entry type, plot the hold and suggest turn times and headings.   It is possible, I have tried it, to just "drive" around the hold or procedure turn by watching the display.   Since the ground track is displayed (right, Dave?) it is trivial to correct for wind.    I recall, with a shudder, holding using the ADF in ancient times back in the 20th century, but the GPS makes all that pretty darn easy to visualize.

 

We can be "Children of the Magenta" even without auto throttle or n axis autopilots. 

 

 

During my instrument training, I would time the turns and try to correct for wind knowing that my 430 had a magenta line I could just follow.  oh well, gotta walk before you can run.

 

Like many on this site, back when I earned my instrument rating, the "magenta line" was something you drew on paper using the crayon from row 3, position 7 of the 96 position Crayola Crayon Box. Sometimes I wake up in a cold sweat from the flashbacks of my ADF training. It is amazing how far the technology has come.  

[cliffy]

I'm still confused on GPSS and holding.

Holds are "timed" maneuvers unless a leg length is specified by ATC. 1 min inbound below 14,000'. The charted holding pattern is not "adjusted" for speed as far as I can tell in a GPS system SO how does the GPSS system account for speed of a/c and winds in the timing of the inbound leg? Secondly, if assigned a "fixed leg distance" how does the GPSS adhere to the ATD (along track distance) for the required inbound turn point?

I'm thinking (before I upgrade) that just flying the "printed" pattern on the depicted chart will not keep me in compliance with the timing or leg distance requirements. 

[Bob_Belville]

I'm still confused on GPSS and holding.

Holds are "timed" maneuvers unless a leg length is specified by ATC. 1 min inbound below 14,000'. The charted holding pattern is not "adjusted" for speed as far as I can tell in a GPS system SO how does the GPSS system account for speed of a/c and winds in the timing of the inbound leg? Secondly, if assigned a "fixed leg distance" how does the GPSS adhere to the ATD (along track distance) for the required inbound turn point?

I'm thinking (before I upgrade) that just flying the "printed" pattern on the depicted chart will not keep me in compliance with the timing or leg distance requirements. 

There are CFIIs here much more qualified to comment but the GTN/GPSS/Autopilot will fly the published procedure, including the hold. I have not had occasion to have ATC spec a hold that is not in the data base. But I have a suspicion that if ATC does give you a "hold @ a fix with a heading and leg instructions that the GTN has a way to enter it. When flying GPSS the A/P is in HDG mode and the heading command comes from the GPS through the GPSS capable device, in our case the Aspen.

[flyboy0681]

There are CFIIs here much more qualified to comment but the GTN/GPSS/Autopilot will fly the published procedure, including the hold. I have not had occasion to have ATC spec a hold that is not in the data base. But I have a suspicion that if ATC does give you a "hold @ a fix with a heading and leg instructions that the GTN has a way to enter it. When flying GPSS the A/P is in HDG mode and the heading command comes from the GPS through the GPSS capable device, in our case the Aspen.

 

Unlike the Garmin 480 unit, the GTN does not have the ability to fly ad-hoc holds. As a matter of fact, I don't think it can fly a published hold, just procedure turns.

[Bob_Belville]

Unlike the Garmin 480 unit, the GTN does not have the ability to fly ad-hoc holds. As a matter of fact, I don't think it can fly a published hold, just procedure turns.

Section 6.7 of my Garmin 725/750 Pilot's Guide deals with flying an Approach with a Hold. It in fact references that: "The Flight Plan Page displays a timer or distance, as appropriate, during the holding pattern. Use this timer or distance to fly the outbound portion of the holding pattern. (The holding pattern is displayed on the Map Page and indicated as the active leg on the Active Flight Plan pages."

[flyboy0681]

Section 6.7 of my Garmin 725/750 Pilot's Guide deals with flying an Approach with a Hold. It in fact references that: "The Flight Plan Page displays a timer or distance, as appropriate, during the holding pattern. Use this timer or distance to fly the outbound portion of the holding pattern. (The holding pattern is displayed on the Map Page and indicated as the active leg on the Active Flight Plan pages."

 

The unit will fly a procedure turn, hold-in-lieu or holding pattern as part of the missed approach, but you can't give it an impromptu hold.

 

For example, if you get the call "Mooney 123Bravo, there is a disabled aircraft on the runway and I'll need you to hold northwest on the 350 radial of the XYZ VOR, four mile segments, standard turns..." The GTN can't handle that.

[Bob_Belville]

The unit will fly a procedure turn, hold-in-lieu or holding pattern as part of the missed approach, but you can't give it an impromptu hold.

 

For example, if you get the call "Mooney 123Bravo, there is a disabled aircraft on the runway and I'll need you to hold northwest on the 350 radial of the XYZ VOR, four mile segments, standard turns..." The GTN can't handle that.

I suppose one way to do it would be to use user defined waypoint(s) which can be defined based on radial and distance. You could then insert waypoint pairs and go from one end to the other inserting as many cycles as you need into the fltplan. I don't know if you'd do pretty racetrack courses or not -- with 4 wp you could. When cleared to proceed you would use dir/fltplan/next fix.

[flyboy0681]

I suppose one way to do it would be to use user defined waypoint(s) which can be defined based on radial and distance. You could then insert waypoint pairs and go from one end to the other inserting as many cycles as you need into the fltplan. I don't know if you'd do pretty racetrack courses or not -- with 4 wp you could. When cleared to proceed you would use dir/fltplan/next fix.

 

I guess that's one way to tackle it, but if the fix is two minutes away thats a lot of work to be doing. Under the circumstances I would hit the OBS button and twist the HSI to the inbound course. 

[Bob_Belville]

And disengage GPSS? Using the HDG bug on the HSI and reversing it every 2 minutes, manually timed?

[flyboy0681]

And disengage GPSS? Using the HDG bug on the HSI and reversing it every 2 minutes, manually timed?

 

Your approach is very interesting to say the least. I just tried it on the simulator and while it can be done as described, it would work best only if the hold is defined upon distance and not one minute segments. I did have a few problems however, first being that the system will create these as flyby waypoints and start the turns rather early, although I suppose you could compensate for that by spreading them out a little further. Second, I had problems getting the circuit to be symmetrical. Lastly, when completing the last segment you'll need to go to the flight plan page and active the next one manually. 

 

I'm also wondering how well it would work if you fly the hold manually and at each segment hit the waypoint key to create one at the exact spot when the turn is about to start.

 

I wonder how this would work in actual conditions, when the stress level could be rather high. And since controllers are counting on you executing the hold accurately, I'm not sure I could trust myself enough to do it this way. 

[Bob_Belville]

Your approach is very interesting to say the least. I just tried it on the simulator and while it can be done as described, it would work best only if the hold is defined upon distance and not one minute segments. I did have a few problems however, first being that the system will create these as flyby waypoints and start the turns rather early, although I suppose you could compensate for that by spreading them out a little further. Second, I had problems getting the circuit to be symmetrical. Lastly, when completing the last segment you'll need to go to the flight plan page and active the next one manually. 

 

I'm also wondering how well it would work if you fly the hold manually and at each segment hit the waypoint key to create one at the exact spot when the turn is about to start.

 

I wonder how this would work in actual conditions, when the stress level could be rather high. And since controllers are counting on you executing the hold accurately, I'm not sure I could trust myself enough to do it this way. 

I agree, I think I would just disengage GPSS and use the 750 map page to manually fly the hold. I probably use the HDG bug to make the turns. When released I'd just have to hit GPSS on the Aspen to continue flight plan.

[kortopates]

It needs to stay simple. For random holds, just use OBS mode set to the inbound course after entering direct to the holding fix. Then use your favorite method to determine the hold entry and steer in heading mode. The GPS will tell you both distance and time back to the fix making it easy to determine when to turn inbound. Sent from my iPhone using Tapatalk

[flyboy0681]

It needs to stay simple. For random holds, just use OBS mode set to the inbound course after entering direct to the holding fix. The use your favorite method to determine the hold entry and steer in heading mode. The GPS will tell you both distance and time back to the fix making it easy to determine when to turn inbound.

 

 

I think we agree that this is the best method. Bob was merely pointing out that it could be done using waypoints and that the A/P could fly the hold. My point was that using waypoints could be rather cumbersome.

 

If only the braintrust's at Garmin could have us enter the hold parameters like they did for the 480.

[midlifeflyer]

I suppose one way to do it would be to use user defined waypoint(s) which can be defined based on radial and distance. You could then insert waypoint pairs and go from one end to the other inserting as many cycles as you need into the fltplan. I don't know if you'd do pretty racetrack courses or not -- with 4 wp you could. When cleared to proceed you would use dir/fltplan/next fix.

 

There are, of course, ways to do it, although I think trying to insert a bunch of cycles into a flight plan is way too much work.

 

One can always select the VOR as a waypoint and use OBS mode to select the inbound course.  If it's a distance hold, just move to HDG mode early and input the intercept.

 

You know, the way we used to do it with VOR and DME?

 

But that's very different than the creation of a hold that can be automatically flown as one can with the 80/480.

 

Edit: Guess I missed kortopates' post and duplicated it.

Edited August 26, 2014 by midlifeflyer

[Marauder]

There are, of course, ways to do it, although I think trying to insert a bunch of cycles into a flight plan is way too much work.

One can always select the VOR as a waypoint and use OBS mode to select the inbound course. If it's a distance hold, just move to HDG mode early and input the intercept.

You know, the way we used to do it with VOR and DME?

But that's very different than the creation of a hold that can be automatically flown as one can with the 80/480.

Edit: Guess I missed kortopates' post and duplicated it.

The OBS mode is definitely the easiest. Mix of the old world and the new world...

[Marauder]

I'm still confused on GPSS and holding.

Holds are "timed" maneuvers unless a leg length is specified by ATC. 1 min inbound below 14,000'. The charted holding pattern is not "adjusted" for speed as far as I can tell in a GPS system SO how does the GPSS system account for speed of a/c and winds in the timing of the inbound leg? Secondly, if assigned a "fixed leg distance" how does the GPSS adhere to the ATD (along track distance) for the required inbound turn point?

I'm thinking (before I upgrade) that just flying the "printed" pattern on the depicted chart will not keep me in compliance with the timing or leg distance requirements.

Ok Cliffy, I took one for the team. Actually I wanted to confirm what I thought I knew.

Whether you are flying a timed or distance hold -- either at the procedure turn or at a missed approach holding point, the GTN series (can't speak for the GNS series but I am guessing it works the same) will calculate out either the distance or the time for you. It will also take in consideration wind correction.

The GPS knows your desired track, the actual track you are flying and your ground speed to come up with what you will need to fly for heading and how long distance or time you will need to fly in the hold.

Pictures are easier to understand. Although this is a no wind situation using the simulator, I can attest that it does in fact give you heading adjustments based on the winds.

This is the VOR RWY A approach into KOXB. I flew the approach using the simulator and did the missed so you can see what it does.

Disregard the ground speeds and the altitudes you see on the simulator. I wanted to move through the approach quicker.

Here is the plane on the final approach path:

Here is the plane beginning to fly the missed approach. Note the course guidance it gives you near the bottom of the map:

Once you get close to the missed approach point it will provide more guidance for you (note the heading and countdown timer in the lower right. This changes if the winds are affecting it):

Once you enter the hold and about to turn, the GPS again gives you a heading. And again this will change with winds. It is telling you to fly 094 now.

Once you begin the outbound leg, a timer or distance calculator is placed on the information line. In this picture it is showing 3 seconds elapsed:

When the time (or distance) is reached, it will give you another turn command, based on winds and reset the clock in this case:

Once you are headed on the inbound leg, the timer starts again. Here it shows starting at 2 seconds and them again at 55 seconds:

If you are doing this with a GPSS equipped autopilot, the magic happens with you watching and monitoring. Pretty amazing stuff.

[Marauder]

As a matter of fact, I don't think it can fly a published hold, just procedure turns.

It can, see my post above.