Track deviation. - NASA ASRS

Attributes
ACN	119741
Time
Date	198908
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : pvd
State Reference	RI
Altitude	msl bound lower : 8000 msl bound upper : 8000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bdl
Operator	common carrier : air carrier
Make Model Name	Medium Transport
Navigation In Use	Other
Flight Phase	cruise other cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 179 flight time total : 3523
ASRS Report	119741
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Shortly after departing pvd we were given direct hfd. Since we were below 10,000' AGL and further than 40 mi, I programmed an RNAV fix for hfd off of pvd VOR (279 degree radial for 51 miles). It is also well known that hfd VOR waivers and scallops quite a bit so RNAV is more accurate to use when navigating to hfd. The first officer had hfd tuned in on his side raw data. About 30 mi from hfd I noticed a slight discrepancy between my bearing pointer to the station and the first officer's. At 25 mi from hfd, I switched the RNAV off and used hfd VOR. There was a 30 degree discrepancy between RNAV and raw data. After double-checking with the first officer and identifying hfd, we agreed the RNAV was wrong and made a 30 degree correction to the left. 3 mins later bradley approach control gave us a 30 degree left heading and asked if we had been navigating direct to hfd. We explained about the RNAV failure and continued to hfd. Upon reaching la guardia, an internal test of the RNAV showed it had failed and I rendered it inoperative in the aircraft logbook (a preflight test earlier that morning had showed it to operate normally).

Original NASA ASRS Text

Title: TRACK DEVIATION.

Narrative: SHORTLY AFTER DEPARTING PVD WE WERE GIVEN DIRECT HFD. SINCE WE WERE BELOW 10,000' AGL AND FURTHER THAN 40 MI, I PROGRAMMED AN RNAV FIX FOR HFD OFF OF PVD VOR (279 DEG RADIAL FOR 51 MILES). IT IS ALSO WELL KNOWN THAT HFD VOR WAIVERS AND SCALLOPS QUITE A BIT SO RNAV IS MORE ACCURATE TO USE WHEN NAVIGATING TO HFD. THE F/O HAD HFD TUNED IN ON HIS SIDE RAW DATA. ABOUT 30 MI FROM HFD I NOTICED A SLIGHT DISCREPANCY BETWEEN MY BEARING POINTER TO THE STATION AND THE F/O'S. AT 25 MI FROM HFD, I SWITCHED THE RNAV OFF AND USED HFD VOR. THERE WAS A 30 DEG DISCREPANCY BETWEEN RNAV AND RAW DATA. AFTER DOUBLE-CHECKING WITH THE F/O AND IDENTIFYING HFD, WE AGREED THE RNAV WAS WRONG AND MADE A 30 DEG CORRECTION TO THE LEFT. 3 MINS LATER BRADLEY APCH CTL GAVE US A 30 DEG LEFT HDG AND ASKED IF WE HAD BEEN NAVIGATING DIRECT TO HFD. WE EXPLAINED ABOUT THE RNAV FAILURE AND CONTINUED TO HFD. UPON REACHING LA GUARDIA, AN INTERNAL TEST OF THE RNAV SHOWED IT HAD FAILED AND I RENDERED IT INOPERATIVE IN THE ACFT LOGBOOK (A PREFLT TEST EARLIER THAT MORNING HAD SHOWED IT TO OPERATE NORMALLY).

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.