SkyDemon Forums

Possible Defect: correct calculation of MSA for legs to account for fly/over/fly by and starting and end points

http://forums.skydemon.aero/Topic32055.aspx

By Tim Dawson - 9/7/2020 10:02:46 AM

Can you give an example route where you observe this happening, please?

SkyDemon does look for obstacles in the "circles" around turns.
By pauls - 9/7/2020 11:10:19 AM

 
Tim Dawson - 9/7/2020 10:02:46 AM
Can you give an example route where you observe this happening, please?

SkyDemon does look for obstacles in the "circles" around turns.

I'll check with the PPL/IR members that raised this - they're based on the continent near the alps! 

However I had a quick play: try

Humberside -> OTR -> Binbrook (town) -> Humberside

There's a mast south of Binrbook which isn't used in the MSA calc (distance 3.4nm)
By lhe - 9/7/2020 12:10:32 PM

 
pauls - 9/7/2020 11:10:19 AM
However I had a quick play: try

Humberside -> OTR -> Binbrook (town) -> Humberside

There's a mast south of Binrbook which isn't used in the MSA calc (distance 3.4nm)



That's a good example.
By Tim Dawson - 9/8/2020 8:53:24 AM

It isn't, because that mast is more than 5nm from Binbrook and 5nm is the default setting for clearance from obstacles (for MSA purposes). If I change my preference to 6nm then the mast is taken account of.
By pauls - 9/8/2020 9:08:22 AM

 
Tim Dawson - 9/8/2020 8:53:24 AM
It isn't, because that mast is more than 5nm from Binbrook and 5nm is the default setting for clearance from obstacles (for MSA purposes). If I change my preference to 6nm then the mast is taken account of.

Tim i i stand correct it's 04nm outside the 5nm radius.

Let me check with the other members that raised the issue and I'll come back to you
By lhe - 9/8/2020 11:03:36 AM

Try this:

Create a route from Sundbro (ESKC) airport, ESE to Skölsta (town), then NNW to STORVRETA VRP.

There is an 874' antenna approximately 1.7 NM SE of Skölsta. The MSA for both route legs is given as 1600'.

My settings for obstruction clearance is 10 NM horizontally, 1000 feet vertically.
By lhe - 9/8/2020 1:37:43 PM

 
lhe - 9/8/2020 11:03:36 AM
Try this:

Create a route from Sundbro (ESKC) airport, ESE to Skölsta (town), then NNW to STORVRETA VRP.

There is an 874' antenna approximately 1.7 NM SE of Skölsta. The MSA for both route legs is given as 1600'.

My settings for obstruction clearance is 10 NM horizontally, 1000 feet vertically.


We've just discovered that if you reverse direction, then SkyDemon will correctly give a 1900' MSA! So there must be some bug here.
By Tim Dawson - 9/10/2020 9:49:50 AM

Thank you. Yes, you have highlighted a bug in our code where certain junctions of legs could fail to correctly pick up obstructions in the arc forming the junction. The next version of SkyDemon will contain a fix to this.
By lhe - 9/10/2020 11:08:57 AM

 
Tim Dawson - 9/10/2020 9:49:50 AM
Thank you. Yes, you have highlighted a bug in our code where certain junctions of legs could fail to correctly pick up obstructions in the arc forming the junction. The next version of SkyDemon will contain a fix to this.

That great. Thank you.

Could you also fix the MSA computation so that obstacles in a semicircle before the starting point of the route is considered in the MSA computations? Just as obstacles in a semicircle after the end point of the route are considered.

When departing from an airport you can't always depart directly in the direction of the route. Runway in use, noise-sensitive areas and/or ATC procedures can mean that you have to fly for some time in the area "before" the route and then obstacles before the route are relevant.
By Tim Dawson - 9/10/2020 1:12:08 PM

Yes, we will do that, but just for the very first leg in your journey.
By pauls - 9/3/2020 9:02:40 PM

I'm posting this on behalf of members of PPL/IR Europe
https://pplir.org/

We have been promoting the use of SD as a useful tool for our members and many of us are loyal users.
We have had a good discussion on the PPL/IR Forum about SD. On the back of this we have collated some feature requests we'd like to raise for consideration
I've raised each one in it's own thread to aid Tim Dawson and the SD team to aid/triage them, but include a link below to the key ones we have raised

Ok so so far we have, in order of priority raised:

* Clearer means of user knowing if VFR or IFR flight rules have been used for purposes of MSA and NOTAMs.
(http://forums.skydemon.aero/Topic32054.aspx?Update=1)
* Possible Defect: correct calculation of MSA for legs to account for fly/over/fly by and starting and end points
(This Thread)
* Allow for built-in Jepp subscription
* Feature Request: Make PLOG better / more Customisable for IFR eg space for notes,clearances and alignment of Nav aids/frequencies to legs

----------------------------------------

This thread covers

* Possible Defect: correct calculation of MSA for legs to account for fly/over/fly by
My top idea would be correct computation of minimum safe altitudes. SD sees to be doing it wrong

As it is, obstacles before and after the route will be ignored, even if they are within the specified distance from the route end. If there is a turn of more than 90° at a waypoint, then obstacles on the outside of the turn will be ignored if they are before or after the ends of the two legs.

There can literally be an obstacle thousands of feet above everything else 1 m from the waypoint and SD will not consider it when computing the MSA.

Oringally waypoints outside any turn were ignored, but a partial fix for turns <90° was made.

Btw, this is relevant for night VFR as well as, according to SERA, minimum altitudes for night VFR are computed the same as for IFR.