Narrative:

Inbound to hdn we were cleared to intercept the hdn 105 degree radial, maintain 13000 ft until established, cleared for the VOR DME B approach to hayden. We intercepted the 105 degree radial and called established at 28 DME. We began a descent to 10000 ft as we thought was depicted on the approach plate. We received a GPWS terrain alert at 11500 ft and initiated a climb until the warning ceased. Further study of the approach plate showed the 10000 ft is for a DME arc and the approach didn't began until 17 DME. Contributing factors include a poor approach brief, moderate turbulence during the brief making it difficult to read the plate, a confusing 10000 ft indication on the approach plate outside the DME arc where a straight in altitude is.

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Original NASA ASRS Text

Title: FLT CREW OF DH8C DEPART ASSIGNED ALT PREMATURELY ON VOR-DME B IAP TO HDN. GET GPWS TERRAIN WARNING.

Narrative: INBOUND TO HDN WE WERE CLRED TO INTERCEPT THE HDN 105 DEG RADIAL, MAINTAIN 13000 FT UNTIL ESTABLISHED, CLRED FOR THE VOR DME B APCH TO HAYDEN. WE INTERCEPTED THE 105 DEG RADIAL AND CALLED ESTABLISHED AT 28 DME. WE BEGAN A DSCNT TO 10000 FT AS WE THOUGHT WAS DEPICTED ON THE APCH PLATE. WE RECEIVED A GPWS TERRAIN ALERT AT 11500 FT AND INITIATED A CLB UNTIL THE WARNING CEASED. FURTHER STUDY OF THE APCH PLATE SHOWED THE 10000 FT IS FOR A DME ARC AND THE APCH DIDN'T BEGAN UNTIL 17 DME. CONTRIBUTING FACTORS INCLUDE A POOR APCH BRIEF, MODERATE TURB DURING THE BRIEF MAKING IT DIFFICULT TO READ THE PLATE, A CONFUSING 10000 FT INDICATION ON THE APCH PLATE OUTSIDE THE DME ARC WHERE A STRAIGHT IN ALT IS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.