Flying to LP Minimums

A break in icy winter weather allowed me to make a short IFR flight from Boeing Field (KBFI) in Seattle to Port Angeles (KCLM), on the north side of the Olympic Peninsula, where I flew the RNAV (GPS) RWY 26 approach. That procedure offers an LP—localizer performance—minimum descent altitude of 760 feet, 160 feet lower than the LNAV MDA of 920 feet.

The LP MDA can be lower because the course narrows as you approach the runway, just like a localizer. Remaining within that funnel allows you to avoid obstacles along the final approach segment that intrude into the constant-width 0.3 nm boundaries used when setting the altitudes for LNAV minimums.

If you have a WAAS-capable, IFR-approved GPS with the appropriate system software, you probably can fly to LP MDAs. Most newer navigators such as the Garmin GTN and later versions of the G1000 have this capability. But check the AFMS for your panel to confirm.

It’s important to understand that the LP line of minimums is to an MDA. Don’t confuse LP with LPV—localizer performance with vertical guidance—which, like an ILS, provides both lateral and vertical guidance to a DA.

And if you fly do fly with a newer WAAS-capable navigator, you will probably get an advisory +V glidepath when you fly an approach with LP minimums. You will see LP+V annunciated on the navigator and on the HSI in a PFD. But that +V guidance only helps you fly a smooth, uninterrupted descent to the MDA. You can’t go below the MDA until you can see the runway environment.

The cloud layers complemented views of the mountains during this scenic New Year’s Day flight.