B757 flight crew reported experiencing a map shift of about a half mile during arrival. Later during...

Attributes
ACN	1447287
Time
Date	201705
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 170 Flight Crew Total 5000 Flight Crew Type 1400
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

A full IRS alignment was completed on the ground prior to flight. There were no position inaccuracies seen on the ground with relation to the runway alignment for takeoff. While climbing through 11;000 ft; we encountered a map shift. LNAV/VNAV were engaged with the center autopilot also on. Aircraft turned about 30 degrees right from previous course to intercept magenta line. Progress page 2 indicated 0.5 NM left of course. Aircraft intercepted course and proceeded on course for remainder of flight with 0 deviation indicated or observed. Later on the arrival and approaching the zzzzz intersection; ATC assigned a heading and asked us to verify that we were on the arrival. We answered in the affirmative and observed 0 deviation from course on progress page 2 with LNAV engaged; reporting that we showed directly over the zzzzz intersection. ATC reported showing us 1 NM west. Both VOR mode selectors were confirmed in the automatic mode.

Original NASA ASRS Text

Title: B757 flight crew reported experiencing a map shift of about a half mile during arrival. Later during arrival; ATC informed the crew they were slightly off course and issued vectors.

Narrative: A full IRS alignment was completed on the ground prior to flight. There were no position inaccuracies seen on the ground with relation to the runway alignment for takeoff. While climbing through 11;000 ft; we encountered a map shift. LNAV/VNAV were engaged with the center autopilot also on. Aircraft turned about 30 degrees right from previous course to intercept magenta line. Progress page 2 indicated 0.5 NM left of course. Aircraft intercepted course and proceeded on course for remainder of flight with 0 deviation indicated or observed. Later on the arrival and approaching the ZZZZZ intersection; ATC assigned a heading and asked us to verify that we were on the Arrival. We answered in the affirmative and observed 0 deviation from course on Progress page 2 with LNAV engaged; reporting that we showed directly over the ZZZZZ intersection. ATC reported showing us 1 NM west. Both VOR mode selectors were confirmed in the AUTO mode.

Data retrieved from NASA's ASRS site 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.