Track deviation. Unable callback.

Attributes
ACN	148045
Time
Date	199005
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : pvd
State Reference	RI
Altitude	msl bound lower : 11000 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zbw
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : instrument pilot : cfi
Experience	flight time last 90 days : 250 flight time total : 11000 flight time type : 3000
ASRS Report	148045
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
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 other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Cleared to cross pmd VOR at 250 KTS 11000'. Flight was from iah to bos. Air carrier flight xx blocked into bos XA36Z. Using LNAV but checked position with raw data 3 or 4 times on way up, per air carrier procedures which do not require 1 pilot to constantly monitor raw data. 7 NM form pvd I got a message on the FMC screen, 'verify position.' immediately tuned pvd VOR and saw it was 45 degrees to the right of the nose at 7 NM. Also glimpsed the tt green (pvd) through a break in the cloud deck below us in the same location as the VOR pointed to. Reached up to select heading select and turn the aircraft toward pvd when ATC asked, 'where are you going?', or words to that effect. We responded with a statement: 'difficulty with the navigation,' and that we were correcting. ATC responded to the effect of, 'no problem, continue on, heading for vectors for ILS 4R in bos.' the captain noticed that the FMC had switched to the right IRS (normally it is on the left). Also over OM runway 4R the FMC was still 4 mi off. I was flying the aircraft as first officer, captain was PNF.

Original NASA ASRS Text

Title: TRACK DEVIATION. UNABLE CALLBACK.

Narrative: CLRED TO CROSS PMD VOR AT 250 KTS 11000'. FLT WAS FROM IAH TO BOS. ACR FLT XX BLOCKED INTO BOS XA36Z. USING LNAV BUT CHKED POS WITH RAW DATA 3 OR 4 TIMES ON WAY UP, PER ACR PROCS WHICH DO NOT REQUIRE 1 PLT TO CONSTANTLY MONITOR RAW DATA. 7 NM FORM PVD I GOT A MESSAGE ON THE FMC SCREEN, 'VERIFY POS.' IMMEDIATELY TUNED PVD VOR AND SAW IT WAS 45 DEGS TO THE RIGHT OF THE NOSE AT 7 NM. ALSO GLIMPSED THE TT GREEN (PVD) THROUGH A BREAK IN THE CLOUD DECK BELOW US IN THE SAME LOCATION AS THE VOR POINTED TO. REACHED UP TO SELECT HDG SELECT AND TURN THE ACFT TOWARD PVD WHEN ATC ASKED, 'WHERE ARE YOU GOING?', OR WORDS TO THAT EFFECT. WE RESPONDED WITH A STATEMENT: 'DIFFICULTY WITH THE NAV,' AND THAT WE WERE CORRECTING. ATC RESPONDED TO THE EFFECT OF, 'NO PROB, CONTINUE ON, HDG FOR VECTORS FOR ILS 4R IN BOS.' THE CAPT NOTICED THAT THE FMC HAD SWITCHED TO THE RIGHT IRS (NORMALLY IT IS ON THE LEFT). ALSO OVER OM RWY 4R THE FMC WAS STILL 4 MI OFF. I WAS FLYING THE ACFT AS F/O, CAPT WAS PNF.

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.