Narrative:

We were given a vector for traffic and then reclred direct to lit. I started a turn using heading select and reselected lit on the FMS. However; I failed to rearm navigation and thus continued toward lit in heading select. As we neared lit; I noticed we were off course somewhat and entered a heading correction. Shortly thereafter; center cleared us direct to the next point beyond lit. No conflicts resulted. This happens for 2 reasons: 1) the angle of bank used by the system is too great in cruise -- 25-30 degrees. Therefore; you must use heading select first and then remember to arm navigation as you approach direct. 2) in my mind at least; the selection of the point on the FMS control panel seems to satisfy my brain. It is easy to forget to rearm the navigation. Of course; a more careful xchk wouldn't hurt either. I would strongly recommend reducing angle of bank used in cruise by the system for such turns. I have heard this was in the works for yrs. I hear many other pilots say they have made the same mistake.

Related reports:

Google
 

Original NASA ASRS Text

Title: AN MD80 PLT COMMENTS THAT BECAUSE THE FMC USES 25-30 DEG BANK ANGLES AT ALT; HE SELECTS HDG FOR COURSE CHANGES AND IN THIS CASE SUBSEQUENTLY GOT OFF TRACK WHEN HE FAILED TO REARM NAV.

Narrative: WE WERE GIVEN A VECTOR FOR TFC AND THEN RECLRED DIRECT TO LIT. I STARTED A TURN USING HDG SELECT AND RESELECTED LIT ON THE FMS. HOWEVER; I FAILED TO REARM NAV AND THUS CONTINUED TOWARD LIT IN HDG SELECT. AS WE NEARED LIT; I NOTICED WE WERE OFF COURSE SOMEWHAT AND ENTERED A HDG CORRECTION. SHORTLY THEREAFTER; CTR CLRED US DIRECT TO THE NEXT POINT BEYOND LIT. NO CONFLICTS RESULTED. THIS HAPPENS FOR 2 REASONS: 1) THE ANGLE OF BANK USED BY THE SYS IS TOO GREAT IN CRUISE -- 25-30 DEGS. THEREFORE; YOU MUST USE HDG SELECT FIRST AND THEN REMEMBER TO ARM NAV AS YOU APCH DIRECT. 2) IN MY MIND AT LEAST; THE SELECTION OF THE POINT ON THE FMS CTL PANEL SEEMS TO SATISFY MY BRAIN. IT IS EASY TO FORGET TO REARM THE NAV. OF COURSE; A MORE CAREFUL XCHK WOULDN'T HURT EITHER. I WOULD STRONGLY RECOMMEND REDUCING ANGLE OF BANK USED IN CRUISE BY THE SYS FOR SUCH TURNS. I HAVE HEARD THIS WAS IN THE WORKS FOR YRS. I HEAR MANY OTHER PLTS SAY THEY HAVE MADE THE SAME MISTAKE.

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.