Tight approach turns

[Paavo]

Hi,

I'm updating some approaches and I've stumbled on a rather serious problem.

As you can see from the picture, FS draws the turn from fix KRD55 to KRD54 using too large radius. All straight legs are TFs, the turn is a CF leg. Course values, as well as the positions of DME fixes, have been checked multiple times.

Is there any way to get a tighter turn or is it hard-coded?

 

[Difar]

Paavo

w/o seeing the code (what rwy/approach/airport is this?) it's hard to say.

By looking at the diagram, I would have to guess the distance or time is off (or possibly one of the waypoints is not in the correct spot).

Yes, it can be fixed, but, is this the correct turn procedure per the instructions...

 

[meshman]

withdrawn.

 

[Paavo]

Let's review the data.


KRD55 is 333 deg MAG from NDB "O" and 5.5N from DME "KRD":

<Waypoint
      lat="59 05 02.5154"          
      lon="22 45 59.3003"             
      waypointType="UNNAMED"        
      magvar="-6.0"            
      waypointRegion="EE"         
      waypointIdent="KRD55">    
</Waypoint>

KRD54 is 321 deg MAG from NDB "O" and 5.4N from DME "KRD":

<Waypoint
      lat="59 04 00.2"          
      lon="22 44 11.3"              
      waypointType="UNNAMED"        
      magvar="-6.0"            
      waypointRegion="EE"         
      waypointIdent="KRD54">    
</Waypoint>

The transition is (a bit messy at the moment):

				<Leg
					type="IF"
					fixType="NDB"
					fixRegion="EE"
					fixIdent="OZ"
					theta="0.0"
					rho="0.0M"
					altitudeDescriptor="A"
					altitude1="457.31708M"
					altitude2="0.0M"/>
				<Leg
					type="TF"
					fixType="NDB"
					fixRegion="EE"
					fixIdent="O"
					turnDirection="L"
					theta="0.0"
					rho="0.0M"
					magneticCourse="321.0"
					altitudeDescriptor="A"
					altitude1="457.31708M"
					altitude2="0.0M"/>
				<Leg
					type="TF"
					fixType="TERMINAL_WAYPOINT"
					fixRegion="EE"
					fixIdent="KRD55"
					turnDirection="L"
					theta="333.0"
					rho="6.7N"
					magneticCourse="333.0"
					altitudeDescriptor="A"
					altitude1="457.3M"
					altitude2="0.0M"/>
				<Leg
					type="CF"
					fixType="TERMINAL_WAYPOINT"
					fixRegion="EE"
					fixIdent="KRD54"
					flyOver="FALSE"
					turnDirection="L"
					recommendedType="NDB"
					recommendedRegion="EE"
					recommendedIdent="O"
					theta="0.0"
					rho="0.5N"
					magneticCourse="141.0"
					distance="0.5N"
					altitudeDescriptor="A"
					altitude1="1500.0M"
					altitude2="0.0M"/>

And the approach from the vectors to final:

				<Leg
					type="IF"
					fixType="TERMINAL_WAYPOINT"
					fixRegion="EE"
					fixIdent="KRD54"
					theta="0.0"
					rho="0.0M"
					altitudeDescriptor="A"
					altitude1="457.31708M"
					altitude2="0.0M"/>	
				<Leg
					type="TF"
					fixType="RUNWAY"
					fixRegion="EE"
					fixIdent="RW14"
					turnDirection="L"
					theta="0.0"
					rho="0.0M"
					magneticCourse="141.0"
					altitudeDescriptor="+"
					altitude1="152.43903M"
					altitude2="0.0M"/>

The chart:

And the profile:

The airport is mostly used by small GA planes, but there are also regular flights with Jetstream 31 and 32. Larger planes can be seen there on very rare occasions, so it doesn't surprise me that the approach is rather tight.

 

[Difar]

Quick question... are you designing this approach?

Because I do not see this in the "stock" airport.

If true your waypoints are 1.4nm (2575.7911 meters) apart, yet your rho says it is 0.5nm seperation. Double check your waypoints lat/longs and if they are correct, then shorten your rho to... say 0.4n.

Let us know what you come up with.

 

[jvile]

Paavo

You need a leg after the TF for the turn.


<Leg type="TF"
fixType="TERMINAL_WAYPOINT"
fixRegion="EE"
fixIdent="KRD55"
flyOver="FALSE"
theta="0.0"
rho="0.0"
magneticCourse="333.0"
altitudeDescriptor="A"
altitude1="457.3M"/>

<Leg type="FC"
fixType="TERMINAL_WAYPOINT"
fixRegion="EE"
fixIdent="KRD55"
flyOver="FALSE"
theta="153.0"
rho="1537.53" <<<<====== Tweak rho. Sometimes it helps and other times it does nothing
magneticCourse="333.0"
distance="1483.66" <<<<<<------ Tweak Distance meter value so the GPS Receiver in the "Load" shows the correct Mile turn for the curve
recommendedType="NDB"
recommendedRegion="EE"
recommendedIdent="O" />

<Leg type="CF"
fixType="TERMINAL_WAYPOINT"
fixRegion="EE"
fixIdent="KRD54"
flyOver="FALSE"
turnDirection="L"

This says fly to the KRD55. Now the FC leg also uses KRD55 from the waypoint to make a turn. The radius of the turn is controlled by distance= and it is going to attach to the next leg which is KRD54.


Optional

If the <Leg type="FC" cannot complete the turn and attach because the KRD54 is too far then add the VI leg just after the FC and before the CF.

<Leg type="VI"
turnDirection="L"
magneticCourse="141.0" /> <<<<===== Tweak the Mag so the VI will align with the CF properly.

 

[scott967]

One thing I have found, looking at my DME arc legs in FS9, is that the GPS draws different paths determined on the aircraft. I don't think it is different for each aircraft, but may just a couple different variants. (First cessna 172 second boeing 734).

scott s.
.

 

[jvile]

I learned a long time ago not to trust the line draw in the GPS approach /transition screen after writing the approach.

The only line draw that is accurate is the Load /Activate and then look at the line draw.

In some cases you have to go back and tweak the approach code because the Load /Activate line draw will not be correct. It will look correct on the approach screen but when loaded there can be distortion in the draw between each type leg.

It is the Load /Activate processed by the .dll that the User plane follows and not the Approach/Transition screen line draw.