Why would an LPV approach be removed from an RNAV approach, leaving only LNAV?
Posted by HungryCommittee3547@reddit | flying | View on Reddit | 11 comments
Happened in the last plate cycle at a local airport many students (used to) use for checkrides and practice instrument approaches. This is in flat midwest territory BTW, no terrain considerations. It seems odd to remove an approach that relies solely on WAAS GPS anyway.
Pitiful_Series_6172@reddit
Runway condition. Runway paint at KAHH faded to the point they lost LPV
flyingron@reddit
Obstacles exist other than terrain. Someone might have constructed a tower or something.
You want to give us a clue which approach you're talking about?
HungryCommittee3547@reddit (OP)
RNAV 36 KCFE
flyingron@reddit
Looks like a lot of trees off the end of the runway, but I'm not a TERPS guru.
HungryCommittee3547@reddit (OP)
Not much in the way of trees off the approach end. However, if you look at the VFR sectional, there are a couple cell towers that top out at 1427ft that are real close to the approach path. This is the only rationale I can think of. I will have to put the plate over the sectional tonight to see how far from the FAF those towers are.
Ok_Pair7351@reddit
Is your reasoning that the trees or other obstacle would block the signal from the ground-based portion of the system? Or that the LPV approach has a shallower/lower approach profile?
Appreciate the response. Currently in the middle of IR training in a plane that only recently had a GPS installed. So my knowledge of GPS systems is definitely weak.
TheGacAttack@reddit
There's no ground-based glideslope on an LPV, and no, trees are not degrading the WAAS. You're thinking like an ILS maybe?
The obstruction clearance standards require that no objects penetrate the OCS (Obstruction Clearance Surface). It's the lower boundary for clear space, to give sufficient protection to approaching aircraft. Understanding the OCS isn't directly tested in IR, but you should read up on it. If you prefer to watch and listen, Seth Lake on YouTube gives a very good (and very dry) presentation on it.
Ok_Pair7351@reddit
Thank you, I appreciate the info!
flyingron@reddit
It's got nothing to do with the signal. It has to do with the possibility of striking them with the airplane.
Spfoamer@reddit
The reason isn't clear, but here's a comparison of the new and old procedures with the changes highlighted. I don't see any changes to obstacles. https://aeronav.faa.gov/d-tpp/2502/compare_pdf/06583r36_cmp.pdf
rFlyingTower@reddit
This is a copy of the original post body for posterity:
Happened in the last plate cycle at a local airport many students (used to) use for checkrides and practice instrument approaches. This is in flat midwest territory BTW, no terrain considerations. It seems odd to remove an approach that relies solely on WAAS GPS anyway.
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