A Bit Over Ninety

It started with a reader question about the RNAV (GPS) Y Rwy 28L at Monterey, CA (KMRY). The question seems simple on the surface: There is a feeder from the SNS VOR to HIXAR on a heading of 146 degrees. The inbound course is 235, meaning an 89-degree turn is required. Are you required to fly the HILPT? AIM 5-4-9 (5) and (6) seem to say yes, but 5-4-5 (8) seems to say a turn from the feeder of less than 90 degrees is implicitly NoPT.

jwanwest

Tuesday, August 01, 2017 at 12:00 AM ET

Verified

Key Takeaways:

The article explains why RNAV (GPS) approaches have a strict 90-degree maximum turn limitation, often requiring a Hold-in-Lieu-of-Procedure Turn (HILPT) even for turns appearing less than 90 degrees.
This 90-degree restriction is due to RNAV systems' "turn anticipation," which initiates turns early and could lead faster aircraft outside protected airspace if the turn angle is too sharp, unlike conventional navigation which allows for larger (120-degree) turns.
Apparent discrepancies in turn requirements are often explained by precise decimal calculations of magnetic variation by approach designers, or an intermediate leg being too short for proper establishment after a turn.
Pilots can often bypass unnecessary HILPTs for slower aircraft by requesting vectors or "straight-in" clearances from ATC, which are considered "legal cheats" to optimize flight paths.

See a mistake? Contact us.

There’s little that’s more essential to an instrument pilot than the approach clearance. We controllers issue them all day long. I fully expect much of my frequency time to be spent issuing approach clearances for either training flights or weather-related needs. Approach Clearance, ATC Notebook, Tarrance Kramer, TAA, PTAC, IFR Magazine, The Terminal Arrival Area makes approach clearances simpler. Intercept vectors that are closer to the FAF have to be shallower. With no associated runway, this approach has only circling minimums. Tarrance Kramer

It started with a reader question about the RNAV (GPS) Y Rwy 28L at Monterey, CA (KMRY). The question seems simple on the surface: “There is a feeder from the SNS VOR to HIXAR on a heading of 146 degrees. The inbound course is 235, meaning an 89-degree turn is required. Are you required to fly the HILPT? AIM 5-4-9 (5) and (6) seem to say yes, but 5-4-5 (8) seems to say a turn from the feeder of less than 90 degrees is implicitly NoPT.”