Auburn, Wash­ing­ton RNAV GPS-A

STEEPER THAN NOR­MAL

Flying - - CONTENTS - By Ja­son Blair and Rob Mark

The only IFR ap­proach to Auburn, Wash­ing­ton (S50), is hardly a pro­ce­dure any­one would con­sider straight­for­ward, de­spite the air­port’s 63-foot field el­e­va­tion. Also known as Dick Scobee Field, named for the late Chal­lenger shut­tle com­man­der, Auburn sits just a few miles south­east of the busy Sea-Tac Class B, while far­ther south­east the ter­rain rises to well over 14,000 feet ap­proach­ing Mount Rainier. Be pre­pared for con­sid­er­able GA traf­fic at Auburn, a known Sea-Tac re­liever.

A. AP­PROACH NOTES

Notes are al­ways im­por­tant, and S50 has a pair of them. One warns pi­lots that the pro­ce­dure is not autho­rized at night, while the other points to a steeper-than-nor­mal 4-de­gree de­scent an­gle, steeper than the 3-de­gree rate most pi­lots ex­pect dur­ing non­preci­sion ap­proaches. This steeper de­scent an­gle de­mands a higher rate of de­scent to reach the min­i­mum de­scent alti­tude in time.

A quick glance at the “Gnd speed-Kts” note of­fers a heads-up on the de­scent rate needed for a safe ap­proach. If, for ex­am­ple, the pro­ce­dure is flown at 120 knots, an 850-foot-per-minute rate of de­scent is re­quired.

B. CIR­CLING MINIMUMS

This Auburn pro­ce­dure is con­sid­ered a cir­cling ap­proach, de­spite a fi­nal ap­proach ra­dial of 331 de­grees. While a GPS ap­proach along the 331 ra­dial will al­low the pi­lot to de­scend even­tu­ally to 920 or 1,040 feet (de­pend­ing on the ap­proach speed), a pi­lot must wait un­til he or she has passed the fi­nal ap­proach fix due to a ra­dio tower sit­ting just out­side the FAF that rises to 853 feet msl.

Due to lo­cal traf­fic, all cir­cling must be con­ducted east of Run­way 16/34 to keep from in­ter­fer­ing with in­bound Sea-Tac traf­fic. This ac­tu­ally puts the cir­cle closer to the ter­rain to the east, and while it can look daunt­ing, there is ac­tu­ally plenty of room.

C. THE RUN­WAY

S50’s Run­way 16/34 is just 3,400 feet long, an­other rea­son only cir­cling minimums are of­fered for air­craft ap­proach cat­e­gories A and B. Im­por­tantly, air­craft with ap­proach speeds greater than 120 knots are not autho­rized to con­duct the ap­proach. But with a short run­way, larger air­craft with ap­proach speeds greater than 120 might find it hard to stop on Auburn’s short run­way any­way.

D. INI­TIAL AP­PROACH FIXES

Pi­lots nav­i­gat­ing on their own may choose from one of two ini­tial ap­proach fixes, one at CIDUG, the other at ORTIN. Pi­lots se­lect­ing the path from CIDUG to ORTIN may skip the hold­ing pat­tern as in­di­cated by the “NoPT” no­ta­tion north­east of CIDUG. Should the pi­lot choose to pro­ceed direct to ORTIN as the ini­tial ap­proach fix, a trip around the hold­ing pat­tern would be re­quired.

E. MISSED AP­PROACH

A missed ap­proach from this GPS ap­proach re­quires a right turn back to ORTIN, where the pi­lot would en­ter the hold. Again, there’s more room lat­er­ally to the east than it might seem at first. Also worth not­ing is that the missed ap­proach point is not ac­tu­ally over the run­way it­self, but rather ½ mile short of the ap­proach end. Pi­lots watch­ing the GPS count down to the MAP must re­mem­ber the dis­tance in­di­cated is from the MAP. The air­port it­self is ac­tu­ally ½ mile far­ther north.

F. MORE ON MINIMUMS

A good case for never bust­ing ap­proach minimums can be made on the Auburn GPS. Re­mem­ber that 853-foot ra­dio tower ad­ja­cent to JISTA? The cross­ing alti­tude is, of course, more than 1,000 feet above that height. But if the air­craft broke out of the clouds just be­fore reach­ing the FAF, the blink­ing lights ahead and be­neath them could fool the pi­lot into think­ing they’re see­ing the run­way end.

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