Following a procedure turn question

[metzgergva]

I just flew into KSBA (a favorite place for me) and it has a nice VOR APP with procedure turn. All worked fine, just the turn was flown a bit wider than on the MFD. I flew it with 180 kts and Flaps APP. The bank was controlled to 20 degrees. Would you expect to fly along the MAP drawing or is this just a symbol?

Screen_12.jpg (114.43 KiB) Viewed 1834 times

[SAS443]

Why are you flying at 180 kts and appr flaps?
The recommended outbound speed for proc.turn in a non-precision approach is 130-140 kts. You are too fast.

It is not a jet airliner.

Try again with vastly reduced speed and maybe it will help with turn radius?

[metzgergva]

You may have been right, but my observation is different. The Procedure Turn is actually drawn with different radius depending on speed, as you can see on the MFD screen and I have done it now with 200 -180 -140. The result is always the same: The commanded bank angle is not sufficient to follow the drawn flight path and the track back is very similar. You can see the 3 turns flown on the attached analysis window. The length of the turn is correctly calculated as it is required with a higher speed and turn radius, it is only the bank angle that requires a bit more. It was 25-22-12.

Screen_15.jpg (64.15 KiB) Viewed 1813 times

[SAS443]

the FMS should fly a standard rate turn (3 degree /second) for all turns. And I can tell your screenshots are indeed little too shalow for that
Example: 147 TAS (140IAS @ 3000ft in your image) would be roughly 22 degree bank angle required for standard rate, given no wind conditions and airspeed change. Your screenshot is showing approx. 12 degrees as you said.

Was there any speed restrictions in your LEGS page?

[metzgergva]

Can't tell you from the top of my head on speed restrictions. Nothing mentioned on the chart. Navigraph does not show anything as speeds and I use their data.

So I think it is back to the AP not applying the correct bank angle for a standard turn.

[KenG]

There are no top speed resitictions, the FMS should be able to caculate from minimum to maximum speeds. Recommend speed is 130 to 140 and that was choosen based on stability of the airplane and workload for the pilot.

You are being a little too literal with the depiction of the procedure turn, I will need to double check, but off the top of my head it may not be 100% correct. It is not flat wrong, just if my memory serves me (I teach three different avionics packages,) there are more steps involved when actually flying the PT.

Remember the procedure turn is not a track the FMS flies, but a series of headings to intercepts. When you make the turn to PT outbound the FMS captures the airplane's current navigation status, applies the PT outbound heading and computes an intercept point. When the FMS reaches the PT outbound intercept point it plots an intercept back to the instrument procedure track. Most of the time it will initially turn to the PT inbound heading, but the FMS will caculate rolling out on the next track.

Thus winds will vary how the PT track will actually look. You can see the same thing happen with the Garmin products that use the real Garmin software in the background.

[metzgergva]

I saw on the PFD the sequence of HDG changes and tje deviation lateral. All that looked good. The FD commanded steeper turns than the aircraft was willing to fly.
Flown by hand with FD guidance will bring you very much on the drawn turn path.
Would you know of bank limits depending on speed?

[jarek]

3° / second (standard turn) or 25 degrees bank whichever is lesser (ICAO procedures)

[metzgergva]

Fully agree with that. So at 140 kts the required bank angle for a standard turn is 21 degrees. Thats what the FD asked for but the actual bank angle flown was half of it.

Flown with 25 degrees bank the speed of standard rate would be 170 kts. So that would then be the maximum speed you would be able to stay on the symbols track if it's radius is drawn acc standard rate of turn, which looks to be right, though I have not measured it first hand. See below now!

All those speeds are of course true air speeds, but at 3000 ft the difference is small.

Addition:
From the screen I measured for the flight done with 180 KIAS at 3000 ft
Shown turn radius für the U - turn is 1.0 nm. That would correspond to 190 KTAS which requires 27.6 degree bank for a standard turn.

[jarek]

No miracles, to follow ICAO rules, outbound track length needs to be extended for higher speeds (1 minute rule)
However, I believe the same speed restrictions should be applicable here as for holds (not because of some strict rule, but FMS needs to apply some internal math). However, as Ken stated, procedural turn is just a symbol. I'm not sure if it is scaled at all.
Important here is entry point where you need to make turn and course that you need to intercept at the end.
In case of KSBA VOR approach it is quite standard procedure.
But in Europe, you can often find procedures, that specify overfly waypoint on the outbound track - 1 minute rule is not applicable in this case.
Then, the picture on PL21 map looks different - it will draw turn trajectory that ends with little arrow slightly curved left or right - depending on course to intercept that closes procedure turn.

[meese91]

Why are you flying at 180 kts and appr flaps?
The recommended outbound speed for proc.turn in a non-precision approach is 130-140 kts. You are too fast.

It is not a jet airliner.

You're right, it's not a jet airliner. I'm a tower controller and I've never seen a tubeliner go faster than 180 at 6dme final (not even everyone's favourite Euro-lowco, who's well known for not caring at all about ATC speed on final). The other day I had a BE20 on our ILS doing 220ias (we see their mode S) at 6dme, 190 at 3dme, and just coming to ca. Vref at about 1dme. Groundspeed checked out. I fricking love turboprops!

[SAS443]

Why are you flying at 180 kts and appr flaps?
The recommended outbound speed for proc.turn in a non-precision approach is 130-140 kts. You are too fast.

It is not a jet airliner.

You're right, it's not a jet airliner. I'm a tower controller and I've never seen a tubeliner go faster than 180 at 6dme final (not even everyone's favourite Euro-lowco, who's well known for not caring at all about ATC speed on final). The other day I had a BE20 on our ILS doing 220ias (we see their mode S) at 6dme, 190 at 3dme, and just coming to ca. Vref at about 1dme. Groundspeed checked out. I fricking love turboprops!

You must've missed out on the Fokker 70/100.
An old acquaintance of mine flew them and he honestly said they could pass the OM at 250knots. Yes that means -2000 ft/min descent and deceleration at the same time

[metzgergva]

No miracles, to follow ICAO rules, outbound track length needs to be extended for higher speeds (1 minute rule)
However, I believe the same speed restrictions should be applicable here as for holds (not because of some strict rule, but FMS needs to apply some internal math). However, as Ken stated, procedural turn is just a symbol. I'm not sure if it is scaled at all.
Important here is entry point where you need to make turn and course that you need to intercept at the end.
In case of KSBA VOR approach it is quite standard procedure.
But in Europe, you can often find procedures, that specify overfly waypoint on the outbound track - 1 minute rule is not applicable in this case.
Then, the picture on PL21 map looks different - it will draw turn trajectory that ends with little arrow slightly curved left or right - depending on course to intercept that closes procedure turn.

From the drawing changes due to speed flown, i think it is not just a symbol and Ken did not say that either. From the measurements on the MFD that I have done and shared, it is clearly corresponding to procedure turn radius. So all is good there. If you fly it with HDG guidance you can match the drawn flight path. It is the AP in FMS mode that banks only half as much as procedure turn requires and that is why the turns gets double the size as documented on the MFD screenshot.
And btw the CRJ clearly is using symbols with little arrows only pointing the HDG as per chart.
I hope that can be easily fixed.