Flying - - DEPARTMENTS - By Rob Mark

Butte Mon­tana VOR-A

Butte, Mon­tana, and its Bert Mooney Air­port (BTM) are nes­tled snug­gly be­tween the Yel­low­stone and Glacier na­tional parks in the south­west­ern por­tion of the state, where cop­per min­ing was once the pri­mary eco­nomic driver. The Butte VOR-A ap­proach to Mooney Air­port seems pretty straight­for­ward, but re­mem­ber, of course, that any ap­proach with­out a run­way num­ber in­di­cates the fi­nal ap­proach course does not tech­ni­cally meet the def­i­ni­tion of a straight-in. The VOR-A’s R098 fi­nal ap­proach course is pretty close, and should, un­der no-wind con­di­tions, of­fer a glimpse of Run­way 12 out the left front cock­pit win­dow if the weather per­mits.

Bert Mooney Air­port’s field el­e­va­tion is 5,551 feet, with ter­rain ris­ing an­other 3,000 feet just east, adding a few chal­lenges dur­ing the ap­proach. The right turn dur­ing the missed ap­proach de­mands pi­lots keep a close eye on their climb rate since just west of BTM the ter­rain is al­ready 1,000 feet higher. Ad­di­tional nearby ob­sta­cles are why the min­i­mums for all cat­e­gories of air­craft are 7,120 feet msl.


While in­bound on R307, fly­ing 127 de­grees to the Cop­per­town VOR (CPN), the pi­lot must be ready to “turn, time and twist,” in IFR-train­ing lan­guage, at the FAF when the course changes to track­ing the R098 out­bound to the air­port. Fail­ure to fly the new course will head air­craft to­ward nearby ter­rain.


While it’s com­mon to use the DME arc to po­si­tion the air­craft on the fi­nal ap­proach when not re­ceiv­ing radar vec­tors, the pi­lot could also pro­ceed to the VOR and head out­bound for a pro­ce­dure turn be­fore re­join­ing the in­bound ra­dial. In an IFR GPS-equipped air­craft, fly­ing di­rectly to the CPN VOR, NUNZU or DMKEX might be pos­si­ble as long as the pi­lot ob­serves the area’s min­i­mum safe al­ti­tudes un­til join­ing an es­tab­lished seg­ment.


Although the R098 pro­vides nearly a straightin to Run­way 12, this ap­proach of­fers only cir­cle-to-land min­i­mums, which opens the op­tion of land­ing on the 5,100-foot Run­way 12/30 or the 9,000-foot Run­way 15/33.


Cir­cling north­east of Run­way 15/33 is not au­tho­rized, a re­stric­tion that might at first seem coun­ter­in­tu­itive con­sid­er­ing the “brown” high-ter­rain de­pic­tions on the plate just west of the run­way. In fact, the ter­rain north and east is even higher, nearly 3,000 feet in some places.


While time in­bound from the fi­nal ap­proach fix can be used to iden­tify the missed ap­proach point, DME will also iden­tify the 10 DME point. But the DME is re­quired for more than sim­ply iden­ti­fy­ing the missed ap­proach point. DME is also re­quired for an air­craft en­ter­ing this ap­proach area from the en route en­vi­ron­ment.


This pro­ce­dure of­fers mul­ti­ple step-down points. Ap­proach­ing from the west of CPN de­mands the air­craft re­main above 12,000 feet as in­di­cated in the MSA chart, while from the north­east, air­craft must re­main at least 10,100 feet. From there, a de­scent to 9,000 feet while on the arc is re­quired un­til es­tab­lished in­bound within 10 miles of the VOR, where a de­scent to 8,200 feet is au­tho­rized. Cross­ing the VOR in­bound, the air­craft may de­scend to 7,120 feet.


The missed ap­proach point at MACXA co­in­cides with the 10 DME but leaves the air­craft short of the air­port. That’s be­cause the pi­lot must see the air­port early enough to land or, if not, have suf­fi­cient dis­tance to make the turn on the missed ap­proach pro­ce­dure while re­main­ing clear of ter­rain. This re­quire­ment is high­lighted by the greater than nor­mal ap­proach vis­i­bil­ity min­i­mums rang­ing from 1¼ to 3 miles de­pend­ing on the air­craft cat­e­gory.

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