 |
37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
|
Pilot of B737 advises there is a discrepancy between the raw data radial of UB881 and the FMS derived track out of cancun VOR on UB881. Displayed track approximates a course of 009 degrees vice charted course of 013 degrees.
| Attributes | |
| ACN | 619625 |
| Time | |
| Date | 200405 |
| Day | Sun |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : mmun.airport |
| State Reference | FO |
| Aircraft 1 | |
| Controlling Facilities | artcc : mmex.artcc tower : ewr.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| ASRS Report | 619625 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | non adherence : clearance non adherence : published procedure other spatial deviation |
| Independent Detector | other flight crewa |
| Resolutory Action | flight crew : returned to assigned airspace |
| Supplementary | |
| Problem Areas | Aircraft Airspace Structure ATC Facility |
| Primary Problem | Airspace Structure |
Narrative:
The FMS on this B737-300 single FMC dual IRS no GPS does not agree after takeoff from cancun VOR radial 013 and a computed course for RNAV operation over UB881 from cancun to mydia intersection. I think that the radial should be more like the 009 degree or 010 degree radial. The FMC computed course is 3.75 degrees west of the radial and grows with distance. Coming across the united states, this aircraft's VOR's were checked against published radial and found on the money. I placed a write up to have maintenance check, and it was found ok. Maybe a type error. Callback conversation with reporter revealed the following information: the reporter advised that he has, in fact, experienced this anomaly in three different aircraft. He commented candidly that he felt the problem actually lies in the cancun area VOR maintenance as he routinely checked the same airborne IRS systems with domestic VOR updating and found them to be extremely accurate.
Original NASA ASRS Text
Title: PLT OF B737 ADVISES THERE IS A DISCREPANCY BETWEEN THE RAW DATA RADIAL OF UB881 AND THE FMS DERIVED TRACK OUT OF CANCUN VOR ON UB881. DISPLAYED TRACK APPROXIMATES A COURSE OF 009 DEGS VICE CHARTED COURSE OF 013 DEGS.
Narrative: THE FMS ON THIS B737-300 SINGLE FMC DUAL IRS NO GPS DOES NOT AGREE AFTER TKOF FROM CANCUN VOR RADIAL 013 AND A COMPUTED COURSE FOR RNAV OP OVER UB881 FROM CANCUN TO MYDIA INTXN. I THINK THAT THE RADIAL SHOULD BE MORE LIKE THE 009 DEG OR 010 DEG RADIAL. THE FMC COMPUTED COURSE IS 3.75 DEGS WEST OF THE RADIAL AND GROWS WITH DISTANCE. COMING ACROSS THE UNITED STATES, THIS ACFT'S VOR'S WERE CHECKED AGAINST PUBLISHED RADIAL AND FOUND ON THE MONEY. I PLACED A WRITE UP TO HAVE MAINT CHECK, AND IT WAS FOUND OK. MAYBE A TYPE ERROR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR ADVISED THAT HE HAS, IN FACT, EXPERIENCED THIS ANOMALY IN THREE DIFFERENT ACFT. HE COMMENTED CANDIDLY THAT HE FELT THE PROB ACTUALLY LIES IN THE CANCUN AREA VOR MAINT AS HE ROUTINELY CHECKED THE SAME AIRBORNE IRS SYSTEMS WITH DOMESTIC VOR UPDATING AND FOUND THEM TO BE EXTREMELY ACCURATE.
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.