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A Potential Killer Waiting to Strike

A Potential Killer Waiting to Strike

  • May
  • 06
  • 2015
  • John Frazier

RNAV GPS 36

When we layer on a non-precision approach coupled to our FMS ability to VNAV down a VDP from the FAF to the runway, the plot really thickens.  If you have been flying lots of VNAV VDPs down to near the pavement without any problem, you are definitely in the danger zone.  Add an approach briefing Lite where you fail, for example, to notice that there is no VASI or PAPI serving runway 36 and that the approach is not authorized at night, and your insurance rates are definitely going to go up.

Lee’s article does a good job of explaining a complex, TERPS-based subject.  Many will not take the time to sort through the technical details, and that is understandable. Not many of us are or want to be TERPS techies.  So here is the bottom line – on any non-precision approach it is possible to have obstacles that do not penetrate the surveyed Obstacle Clearance Surface (OCS) but can penetrate the VDP line between the FAF and the pavement.  When this happens, you will not be able to tell it from the information on the published chart, although, as Lee explains, there may be clues.  No VASI or PAPI, may be one of them.

We and everybody else in the training world preaches that you are visual below the MDA, but Lee Smith’s article puts some clothes on the concept.  The risks are real – don’t get bit. 


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