MD81 experiences loss of shero waypoint on triss RNAV SID/txk transition from dfw.

Attributes
ACN	700940
Time
Date	200606
Local Time Of Day	0601 To 1200
Place
Locale Reference	intersection : shero
State Reference	TX
Altitude	msl single value : 23000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw.artcc
Operator	common carrier : air carrier
Make Model Name	MD-81
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : intermediate altitude
Route In Use	departure sid : triss.rnav
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	700940
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	700939
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance non adherence : published procedure other spatial deviation
Resolutory Action	controller : issued new clearance controller : issued advisory
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft Chart Or Publication
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation

Narrative:

On flight from dfw to ewr; we plugged in and flew the TRISS2/texarkana transition. During climb out; ATC gave us a call and said we were north of course and on the wrong 'radial.' I mentioned that we were on the RNAV departure; 'radials were north/a.' turns out; intersection shero on the SID had dropped out of the GPS 'legs' and the airplane was flying a direct course from triss to texarkana. The captain and I were stunned when we realized something was awry. We flew 3 to 4 miles north of shero intersection and didn't have a clue how it happened. Angst ensued when we were given the 'phone number to call when we land for possible deviation.' bottom line: how the hell did that happen?!! We flew the SID without any assigned heading changes or 'directs.' still not sure how 'shero' dropped out of the RNAV departure on GPS.

Original NASA ASRS Text

Title: MD81 EXPERIENCES LOSS OF SHERO WAYPOINT ON TRISS RNAV SID/TXK TRANSITION FROM DFW.

Narrative: ON FLT FROM DFW TO EWR; WE PLUGGED IN AND FLEW THE TRISS2/TEXARKANA TRANSITION. DURING CLBOUT; ATC GAVE US A CALL AND SAID WE WERE N OF COURSE AND ON THE WRONG 'RADIAL.' I MENTIONED THAT WE WERE ON THE RNAV DEP; 'RADIALS WERE N/A.' TURNS OUT; INTERSECTION SHERO ON THE SID HAD DROPPED OUT OF THE GPS 'LEGS' AND THE AIRPLANE WAS FLYING A DIRECT COURSE FROM TRISS TO TEXARKANA. THE CAPT AND I WERE STUNNED WHEN WE REALIZED SOMETHING WAS AWRY. WE FLEW 3 TO 4 MILES N OF SHERO INTERSECTION AND DIDN'T HAVE A CLUE HOW IT HAPPENED. ANGST ENSUED WHEN WE WERE GIVEN THE 'PHONE NUMBER TO CALL WHEN WE LAND FOR POSSIBLE DEV.' BOTTOM LINE: HOW THE HELL DID THAT HAPPEN?!! WE FLEW THE SID WITHOUT ANY ASSIGNED HDG CHANGES OR 'DIRECTS.' STILL NOT SURE HOW 'SHERO' DROPPED OUT OF THE RNAV DEP ON GPS.

Data retrieved from NASA's ASRS site as of January 2009 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.