Narrative:

While climbing through approximately 25000 ft on the TRISS2 RNAV departure; ATC called and asked 'where were we going?' the first officer responded that 'we were direct txk' since that was the next active waypoint. ATC asked if we were on the departure and we replied that we were on the TRISS2 departure; however; the previous controller had given us a shortcut direct triss. After much discussion; ATC eventually advised that we had missed the shero waypoint. ATC went on to say that although there was no traffic conflict; it did appear to be a pilot deviation. We examined the legs page and noted that for some unknown reason shero was no longer stored on the FMS flight plan. After triss we should have tracked to shero but did not. The controller was correct and I believe we were about 3-4 miles north of course. The question is; why did shero disappear from the FMS flight plan? The first officer loaded the TRISS2 at the gate and we both verbally checked off each waypoint and the departure runway on the FMS against the chart for accuracy. There was no discrepancy noted and all waypoints were correctly shown on the legs page and the departure routing was accurately depicted on the nd. The only edit we eventually made was direct triss. This should not have deleted shero but I believe this is what happened. There was never any flight plan discontinuity shown. I have done this departure a number of times already and have not had any problems. I suspect that there could be a software problem in the FMS unit on that airplane so a logbook entry was made. I have given this event a lot of thought and can only come up with a few possibilities regarding this event. First; I believe that once we selected direct triss that somehow caused shero to disappear. ATC did say the exact problem had happened many times before for flts that were given the direct triss shortcut. Could there be a software glitch on some aircraft? Or second; if shero was somehow never inserted into the FMS flight plan; then why wasn't it? It should have been automatically inserted with all of the many other RNAV waypoints. To manually insert shero would result in an unauthorized edit of the departure. Third and finally; I also note that to properly insert this departure requires that the txk transition be selected along with the departure runway. Since there are no other transitions; I believe that this extra (but necessary) step could possibly induce errors. Callback conversation with reporter revealed the following information: reporter advised that a post flight brief with the first officer determined she was unsure whether she had selected the 'transition' when installing the triss RNAV SID. Reporter suspects that was not done and the route discontinuity closed in error. He noted that many of the new RNAV sids include both SID tracks and transition tracks. Some; however; like the triss; have only the single transition which is flown by al users. He wonders why it isn't simply a SID route all the way to txk; thus removing the potential for failing to select a specific transition when there is really no reason to require the separate action. Reporter was somewhat dismayed that the radar controller appeared to have a prepared script for such deviations which he read in the clear. He felt a better solution would have been to query him regarding their track when the possible deviation first became obvious rather than waiting until they were past shero; the point of maximum possible displacement from the transition track. He also noted that the dfw RNAV SID advisory notice at no time addresses the unusual aspect of needing to select a transition on a departure which has only a single transition available; an illogical construction on its face. He noted a review of that notice does reveal the statement that 'strict compliance with the lateral and vertical tracks is imperative' which language should certainly have alerted them to be extra cautious in loading and verifying their departure routing. It also admonishes flight crews to not 'manually construct RNAV procedures.' manually closing a discontinuity would be in violation of that admonition.

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Original NASA ASRS Text

Title: MD80 EXPERIENCES TRACK DEV ON TRISS RNAV SID FROM DFW.

Narrative: WHILE CLBING THROUGH APPROX 25000 FT ON THE TRISS2 RNAV DEP; ATC CALLED AND ASKED 'WHERE WERE WE GOING?' THE FO RESPONDED THAT 'WE WERE DIRECT TXK' SINCE THAT WAS THE NEXT ACTIVE WAYPOINT. ATC ASKED IF WE WERE ON THE DEP AND WE REPLIED THAT WE WERE ON THE TRISS2 DEP; HOWEVER; THE PREVIOUS CTLR HAD GIVEN US A SHORTCUT DIRECT TRISS. AFTER MUCH DISCUSSION; ATC EVENTUALLY ADVISED THAT WE HAD MISSED THE SHERO WAYPOINT. ATC WENT ON TO SAY THAT ALTHOUGH THERE WAS NO TFC CONFLICT; IT DID APPEAR TO BE A PLT DEV. WE EXAMINED THE LEGS PAGE AND NOTED THAT FOR SOME UNKNOWN REASON SHERO WAS NO LONGER STORED ON THE FMS FLT PLAN. AFTER TRISS WE SHOULD HAVE TRACKED TO SHERO BUT DID NOT. THE CTLR WAS CORRECT AND I BELIEVE WE WERE ABOUT 3-4 MILES N OF COURSE. THE QUESTION IS; WHY DID SHERO DISAPPEAR FROM THE FMS FLT PLAN? THE FO LOADED THE TRISS2 AT THE GATE AND WE BOTH VERBALLY CHKED OFF EACH WAYPOINT AND THE DEP RWY ON THE FMS AGAINST THE CHART FOR ACCURACY. THERE WAS NO DISCREPANCY NOTED AND ALL WAYPOINTS WERE CORRECTLY SHOWN ON THE LEGS PAGE AND THE DEP ROUTING WAS ACCURATELY DEPICTED ON THE ND. THE ONLY EDIT WE EVENTUALLY MADE WAS DIRECT TRISS. THIS SHOULD NOT HAVE DELETED SHERO BUT I BELIEVE THIS IS WHAT HAPPENED. THERE WAS NEVER ANY FLT PLAN DISCONTINUITY SHOWN. I HAVE DONE THIS DEP A NUMBER OF TIMES ALREADY AND HAVE NOT HAD ANY PROBS. I SUSPECT THAT THERE COULD BE A SOFTWARE PROB IN THE FMS UNIT ON THAT AIRPLANE SO A LOGBOOK ENTRY WAS MADE. I HAVE GIVEN THIS EVENT A LOT OF THOUGHT AND CAN ONLY COME UP WITH A FEW POSSIBILITIES REGARDING THIS EVENT. FIRST; I BELIEVE THAT ONCE WE SELECTED DIRECT TRISS THAT SOMEHOW CAUSED SHERO TO DISAPPEAR. ATC DID SAY THE EXACT PROB HAD HAPPENED MANY TIMES BEFORE FOR FLTS THAT WERE GIVEN THE DIRECT TRISS SHORTCUT. COULD THERE BE A SOFTWARE GLITCH ON SOME ACFT? OR SECOND; IF SHERO WAS SOMEHOW NEVER INSERTED INTO THE FMS FLT PLAN; THEN WHY WASN'T IT? IT SHOULD HAVE BEEN AUTOMATICALLY INSERTED WITH ALL OF THE MANY OTHER RNAV WAYPOINTS. TO MANUALLY INSERT SHERO WOULD RESULT IN AN UNAUTHORIZED EDIT OF THE DEP. THIRD AND FINALLY; I ALSO NOTE THAT TO PROPERLY INSERT THIS DEP REQUIRES THAT THE TXK TRANSITION BE SELECTED ALONG WITH THE DEP RWY. SINCE THERE ARE NO OTHER TRANSITIONS; I BELIEVE THAT THIS EXTRA (BUT NECESSARY) STEP COULD POSSIBLY INDUCE ERRORS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THAT A POST FLT BRIEF WITH THE FO DETERMINED SHE WAS UNSURE WHETHER SHE HAD SELECTED THE 'TRANSITION' WHEN INSTALLING THE TRISS RNAV SID. RPTR SUSPECTS THAT WAS NOT DONE AND THE RTE DISCONTINUITY CLOSED IN ERROR. HE NOTED THAT MANY OF THE NEW RNAV SIDS INCLUDE BOTH SID TRACKS AND TRANSITION TRACKS. SOME; HOWEVER; LIKE THE TRISS; HAVE ONLY THE SINGLE TRANSITION WHICH IS FLOWN BY AL USERS. HE WONDERS WHY IT ISN'T SIMPLY A SID RTE ALL THE WAY TO TXK; THUS REMOVING THE POTENTIAL FOR FAILING TO SELECT A SPECIFIC TRANSITION WHEN THERE IS REALLY NO REASON TO REQUIRE THE SEPARATE ACTION. RPTR WAS SOMEWHAT DISMAYED THAT THE RADAR CTLR APPEARED TO HAVE A PREPARED SCRIPT FOR SUCH DEVIATIONS WHICH HE READ IN THE CLEAR. HE FELT A BETTER SOLUTION WOULD HAVE BEEN TO QUERY HIM REGARDING THEIR TRACK WHEN THE POSSIBLE DEV FIRST BECAME OBVIOUS RATHER THAN WAITING UNTIL THEY WERE PAST SHERO; THE POINT OF MAXIMUM POSSIBLE DISPLACEMENT FROM THE TRANSITION TRACK. HE ALSO NOTED THAT THE DFW RNAV SID ADVISORY NOTICE AT NO TIME ADDRESSES THE UNUSUAL ASPECT OF NEEDING TO SELECT A TRANSITION ON A DEP WHICH HAS ONLY A SINGLE TRANSITION AVAILABLE; AN ILLOGICAL CONSTRUCTION ON ITS FACE. HE NOTED A REVIEW OF THAT NOTICE DOES REVEAL THE STATEMENT THAT 'STRICT COMPLIANCE WITH THE LATERAL AND VERT TRACKS IS IMPERATIVE' WHICH LANGUAGE SHOULD CERTAINLY HAVE ALERTED THEM TO BE EXTRA CAUTIOUS IN LOADING AND VERIFYING THEIR DEP ROUTING. IT ALSO ADMONISHES FLT CREWS TO NOT 'MANUALLY CONSTRUCT RNAV PROCS.' MANUALLY CLOSING A DISCONTINUITY WOULD BE IN VIOLATION OF THAT ADMONITION.

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.