|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||1801 To 2400|
|Locale Reference||atc facility : dru|
|Altitude||msl bound lower : 14000|
msl bound upper : 14000
|Make Model Name||Small Aircraft, Low Wing, 2 Eng, Retractable Gear|
|Flight Phase||cruise other|
|Route In Use||enroute airway : v343|
|Function||flight crew : single pilot|
|Qualification||pilot : commercial|
pilot : instrument
|Experience||flight time last 90 days : 100|
flight time total : 5000
|Affiliation||government : faa|
|Function||controller : radar|
|Qualification||controller : radar|
|Anomaly||aircraft equipment problem : critical|
non adherence : clearance
other spatial deviation
|Independent Detector||other controllera|
|Resolutory Action||controller : issued new clearance|
none taken : detected after the fact
|Air Traffic Incident||other|
The flight was an air ambulance run from mso to hln to shr and return. All en route (between VOR's) legs were short except V343 between bzn and dru. At the midpoint of that leg the navigation's were indicating on centerline and did not change indications after frequency change to dru. At an estimated (dru has no DME) 25-30 mi from dru center advised the aircraft was 8 mi north of centerline. Indications were on centerline for both VOR CDI's and the autoplt heading bug hadn't had to be moved but 2 or 3 degrees the whole time. A request to fly a particular heading was received and complied with. At approximately 20 mi out both CDI's swung hard left and an intercept of 45 degrees would have been needed to cross dru. The problem was written up in the maintenance logs. Radio tech's state that because the system uses shared components, both CDI's would respond alike to an erroneous input when tuned to the same frequency. In this case a lack of receiver sensitivity may also have had an effect. Had the ATC specialist commented earlier an 8 mi course correction would have been unnecessary and would have alerted the crew that the navigation's were not to be entirely trusted.
Original NASA ASRS Text
Title: BOTH VOR INDICATORS SHOWED ACFT TO BE ON COURSE WHEN IN FACT ACFT WAS 8 MILES NORTH OF COURSE.
Narrative: THE FLT WAS AN AIR AMBULANCE RUN FROM MSO TO HLN TO SHR AND RETURN. ALL ENRTE (BTWN VOR'S) LEGS WERE SHORT EXCEPT V343 BTWN BZN AND DRU. AT THE MIDPOINT OF THAT LEG THE NAV'S WERE INDICATING ON CENTERLINE AND DID NOT CHANGE INDICATIONS AFTER FREQ CHANGE TO DRU. AT AN ESTIMATED (DRU HAS NO DME) 25-30 MI FROM DRU CENTER ADVISED THE ACFT WAS 8 MI N OF CENTERLINE. INDICATIONS WERE ON CENTERLINE FOR BOTH VOR CDI'S AND THE AUTOPLT HDG BUG HADN'T HAD TO BE MOVED BUT 2 OR 3 DEGS THE WHOLE TIME. A REQUEST TO FLY A PARTICULAR HDG WAS RECEIVED AND COMPLIED WITH. AT APPROX 20 MI OUT BOTH CDI'S SWUNG HARD LEFT AND AN INTERCEPT OF 45 DEGS WOULD HAVE BEEN NEEDED TO CROSS DRU. THE PROB WAS WRITTEN UP IN THE MAINT LOGS. RADIO TECH'S STATE THAT BECAUSE THE SYS USES SHARED COMPONENTS, BOTH CDI'S WOULD RESPOND ALIKE TO AN ERRONEOUS INPUT WHEN TUNED TO THE SAME FREQ. IN THIS CASE A LACK OF RECEIVER SENSITIVITY MAY ALSO HAVE HAD AN EFFECT. HAD THE ATC SPECIALIST COMMENTED EARLIER AN 8 MI COURSE CORRECTION WOULD HAVE BEEN UNNECESSARY AND WOULD HAVE ALERTED THE CREW THAT THE NAV'S WERE NOT TO BE ENTIRELY TRUSTED.
Data retrieved from NASA's ASRS site as of August 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.