Quick post on ENR Obstacles, I am preparing a course where we need to design several parts of an instrument flight procedure and I usually start with the minimum sector altitudes (MSA)

To calculate these we need to do a 25NM radius around a significant point, ARP or HRP, in my case was using ARP as it was a MSA for a PBN exercise. We use terrain models and man made obstacle data usually published in the AIP. I normally add a 100m margin to terrain to take into consideration unaccounted obstacles (Thanks to mentor Nick Gribble) . Why? Very easy obstacles 100m+ AGL need to be published in the AIP but those less than that not really

See the following image, terrain is the control for the MSA however in the obstacle dataset (ENR 5.4) from the country there are thousands of obstacles but not the two shown as I suppose they are less than 100m height. So on top of terrain we need to add those man made objects but have no clue their height above the ground, hence why I add 100m AGL

So issue is the minimum obstacle clearance (MOC) could be less than the safety margin we think we are adding.

In essence maybe we shouldn’t filter the obstacles presented or provided for procedure design, States should just provide the raw data and with today’s computer graphics, dedicated workstations, hardware acceleration and our brain it shouldn’t be a problem

P.S. Have you thought above your process or just follow blindly the rules?


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