COMMUTER FLC DID NOT FOLLOW THE NAV ROUTING TO WHICH CLRED BY ATC DUE TO A LACK OF COM WITH ATC.

Narrative

DURING A COMMUTER FLT BTWN GRAND CANYON; AZ; AND LAS VEGAS; NV; CREW FILED IFR FLT PLAN WITH PRESCOTT RADIO BECAUSE OF A LINE OF CLOUDS; RAIN; AND SNOW SHOWERS APPROX HALFWAY TO LAS VEGAS. ACFT AND CREW WERE FULLY CERTIFIED FOR IFR FLT ALTHOUGH FLTS ARE NORMALLY CONDUCTED SINGLE PLT VFR. GCN GND CTLR ISSUED CLRNC AS FOLLOWS: 'CLRED TO LAS VEGAS ARPT AS FILED; CLB AND MAINTAIN 10000; DEP FREQ LA CTR ON 124.2; SQUAWK ABCD.' CREW UNDERSTOOD AS FILED TO BE THE DIRECT ROUTING USED BY NEARLY ALL IFR CANYON OPERATORS AND BELIEVED THAT WAS THE ROUTING REQUESTED OF PRESCOTT FSS. AFTER AN UNEVENTFUL TKOF IN EXCELLENT VFR CONDITIONS; CREW TURNED ON COURSE DIRECT TO LAS HDG 265 DEG. RADIO CONTACT WITH LA CTR WAS ESTABLISHED PASSING 9000 FT AT APPROX 3 DME W OF GCN. LA RPTED: 'STANDBY FOR RADAR IDENT.' FREQ WAS VERY BUSY. CONTINUED CLB TO 10000 STILL IN GOOD VFR CONDITIONS. APPROX 5 MINS LATER; STILL VFR; LA CTR SAID; 'RADAR CONTACT 15 MI W GCN; WHAT ARE YOU SHOWING AS YOUR RTE CLRNC?' 'WE'RE SHOWING DIRECT LAS VEGAS.' 'WE HAVE YOU GCN; V210 PEACH SPRINGS CROWE 6 ARR.' AFTER REQUESTING DIRECT ROUTING; LA CTR APPROVED. SHORTLY THEREAFTER; WE ENTERED IMC. CREW APOLOGIZED FOR COM ERROR -- CTLR SOUNDED VERY ANNOYED. CREW OFFERED TO ACCEPT 12000 FT IN ORDER TO ALLEVIATE ANY POTENTIAL TFC CONFLICTS UP AHEAD AND WAS CLRED TO 12. CONTRIBUTING FACTORS: POOR COM WITH FSS; FREQ CONGESTION ON LA CTR; POOR RADAR AND COM FREQ COVERAGE IN SECTOR IN QUESTION. CORRECTIVE ACTION: REQUEST FULL RTE CLRNC FROM CLRNC DELIVERY INSTEAD OF 'AS FILED' WHENEVER IN DOUBT.