B757 flight crew experienced an FMC navigation error departing pbi; requests radar vectors for the r...

Attributes
ACN	954146
Time
Date	201106
Local Time Of Day	1801-2400
Place
Locale Reference	PBI.TRACON
State Reference	FL
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Climb
Component
Aircraft Component	FMS/FMC
Person 1
Function	First Officer Pilot Flying
Experience	Flight Crew Last 90 Days 98 Flight Crew Total 11000 Flight Crew Type 2000
Person 2
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 40 Flight Crew Total 11000 Flight Crew Type 4000
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types

Narrative:

After takeoff as the pilot flying; I called for LNAV at 400 ft AGL and followed my flight director directions to make a right turn. The initial departure went normal. The tower instructed us to contact pbi departure. Upon initial contact; the controller asked us where we were going. Apparently we were not on the tbird 1. Our box looked good and we were on the magenta line; but clearly; according to the controller; we were off course. We advised the controller we were following our navigation and we were on target. The captain (pilot not flying) then advised the controller that our navigation was in error. We then received vectors for the remainder of the flight. In addition; as a crew; we attempted to evaluate what may be wrong; but were unable to come up with any answers. That said the CDU did display two messages off and on throughout the flight. The first was IRS navigation only and the other was purge updates-position 2. As a last note; on final approach our GPWS went off telling us to pull up. We were VFR; on glide slope and evaluated our situation determining that a) we were safe and B) this was related to the IRS showing our position to be miles from where we actually were. The captain selected the terrain button on the panel in front of him silencing the warning. We landed uneventfully.

Original NASA ASRS Text

Title: B757 flight crew experienced an FMC navigation error departing PBI; requests Radar vectors for the remainder of the flight. The CDU displayed two messages off and on throughout the flight; IRS NAV only and Purge Updates-POS 2.

Narrative: After takeoff as the pilot flying; I called for LNAV at 400 FT AGL and followed my flight director directions to make a right turn. The initial departure went normal. The Tower instructed us to contact PBI Departure. Upon initial contact; the Controller asked us where we were going. Apparently we were not on the TBIRD 1. Our box looked good and we were on the magenta line; but clearly; according to the Controller; we were off course. We advised the Controller we were following our navigation and we were on target. The Captain (pilot not flying) then advised the Controller that our navigation was in error. We then received vectors for the remainder of the flight. In addition; as a crew; we attempted to evaluate what may be wrong; but were unable to come up with any answers. That said the CDU did display two messages off and on throughout the flight. The first was IRS NAV only and the other was Purge Updates-POS 2. As a last note; on final approach our GPWS went off telling us to pull up. We were VFR; on glide slope and evaluated our situation determining that A) we were safe and B) this was related to the IRS showing our position to be miles from where we actually were. The Captain selected the Terrain button on the panel in front of him silencing the warning. We landed uneventfully.

Data retrieved from NASA's ASRS site as of April 2012 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.

B757 flight crew experienced an FMC navigation error departing pbi; requests radar vectors for the remainder of the flight. The CDU displayed two messages off and on throughout the flight; IRS navigation only and purge updates-position 2.