Flying WAAS

After what seems an interminable stretch of bad weather, even by Seattle standards, a warm front moved through the Pacific Northwest today. The clouds didn’t part, but they spilled only light rain showers, and most importantly, the freezing level soared to around 6000 feet, high enough for me start up the Beechcraft A36 and log some RNAV (GPS) approaches that take advantage of the updated WAAS capabilities of the Garmin GNS530W installed in the instrument panel. Being a belt-and-suspenders guy, I brought along my portable Garmin GPSMAP 396 GPS, which can display real-time weather information beamed via XM radio signals.

(You can find more pictures and charts and a GPS track file [.kmz] from the flight that you load into Google Earth in one of my public SkyDrive folders.)

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I departed about 1230 PST (2030Z) from Renton, WA (KRNT) on an IFR flight plan to Skagit/Bayview (KBVS). I was cleared to climb to 4000 and proceed via the PAE VOR near Everett, WA to KBVS. Given the reported weather at Skagit, I expected to fly the RNAV (GPS) Rwy 10 approach.

The airspace north of Seattle is a mosaic, with pieces under the jurisdiction of Seattle Approach, Seattle Center, and NAS Whidbey Island Approach. After takeoff to the south, I was vectored around to the northwest (the better to avoid conflicts with traffic using Boeing Field [KBFI] and Sea-Tac [KSEA]) and then cleared direct to an initial fix for the approach (see the blue GPS track of the entire flight overlaid on the sectional chart above).

Although the clouds were free of ice and serious rain, the famous Puget Sound Convergence Zone made its presence felt. I rode through continuous light turbulence in and occasionally between layers of dense clouds from around Everett north.

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Thanks to the display on the GPSMAP 396, I knew that the weather at KBVS was well above the lowest minimums established for the approach (353 feet above the runway and 1.25 miles visibility), so I loaded the procedure into the GNS530W as soon as I was cleared to SOCLO, one of the initial fixes for the procedure.

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A few miles southeast of SOCLO, the Whidbey Approach turned me loose: "Bonanza 46 Foxtrot, cross SOCLO at 4000, cleared the RNAV runway 10 approach."

From this point, I’m left to fly the procedure on my own. Before WAAS, I’d have been busy during the holding-pattern course reversal (which, given my arrival from the southeast, was best accomplished with a parallel entry into the oval holding pattern).

For reasons I’ve never understood, many pilots intensely dislike parallel entries. The GNS530W, however, makes the U-turn a non-event. The moving map shows your airplane’s position relative to the charted hold, and the unit prompts you to fly specific headings. It even starts a timer at the appropriate moment. Just follow the magenta line, and you’ll fly a textbook entry and then track directly back to the initial fix for the approach.

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A few minutes later, I was heading directly toward the runway, riding the GPS-generated glideslope toward the LPV DA of 497 feet MSL. These GPS-based glideslopes are the real magic behind WAAS. In effect, they turn most approaches into ILS-like procedures that are typically available only at big airports. The Whidbey controller cleared me to switch the CTAF and asked me to report on the ground.

On such a dreary day, I had the airport mostly to myself. The only other traffic was a Robinson R22 helicopter working in the traffic pattern. I landed and cleared the runway. I couldn’t talk to Whidbey on the radio, so I drew my cell phone and called the Seattle Flight Service Station, which relayed my arrival to Whidbey and then obtained my IFR clearance back to Renton. I was back in the air in just a few minutes, well ahead of my clearance void time. Whidbey confirmed radar contact and aimed me west of Paine Field (KPAE) en route back to Renton at 3000 feet.

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The ride home was smoother, and the efficient, friendly controllers soon had me set up for the RNAV (GPS) Rwy 15 approach to KRNT.

But as often happens, things don’t work out quite as planned. After several handoffs, the last controller issued my approach clearance: "Bonanza 46 Foxtrot, cross LUTSY at 2000, cleared the RNAV runway 15 approach."

I had just gotten established on the intermediate segment of the procedure from LUTSY when the controller announced Plan B.

"Bonanza 46 Foxtrot, there’s a Boeing 737 first flight about to depart Renton, I need to turn you east and bring you back around."

Renton is home to the Boeing 737 factory, and because of rising terrain south of the airport, fledgling Boeing jets always take off to the north, over Lake Washington. This jet would be aimed directly at me if I didn’t turn.

A series of vectors followed, driving me in a neat box pattern back around to the north (see the GPS track). I twisted knobs and punched buttons to reload the procedure, and in a few minutes, I was back at LUTSY, this time for good. I broke through the clouds in plenty of time to see the runway, and once again, I rode a GPS glideslope right to the touchdown zone on the runway. Just like Flight Simulator….

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If you haven’t had the opportunity to see WAAS in action, track down a pilot who has a WAAS-capable unit and go for a ride. It’s terrific leap forward in safety and utility for pilots who fly IFR.

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