Narrative:

Prior to departure, in run-up bloc at runway 31C mdw, the 'heading' warnings appeared in HSI. Determined that copilot's HSI was the cause and 'slaved' to correct heading. On tof roll at approximately vr (rotation) heading flags again appeared, with what appeared to be 30 degree split. Main concern during this phase of flight was to 'clean' up aircraft and continue with departure 'SID.' however, during turn, the HSI precession was increasing. Decided to level wings and slave gyros to eliminate 'heading' flags which resulted in correct heading information. At this time departure requested and received an 'immediate right turn to 170 degrees.' a few mins later a climb and left turn bac to SID procedure was issued along with a verbal description, by departure control, of the turn required after tof. Breadown of events: the run-up area of runway 31C at mdw has previously resulted in comparative monitor warnings, 'heading' flags. Is there a magnetic anomaly at this location? It is absolutely more important to 'fly' the aircraft at critical flight phases and fix previous problems before continuing into more complex flight environments, ie, heavy IFR/turbulence/icing/thunderstorm areas. When air traffic control observes an impending deviation from a predetermined flight path, should they not immediately inquire, rather than wait to issue corrective actions? Should pilots inform ATC of what is perceived as a minor problem with a quic solution every flight? Ie, fix problem or comply with ATC immediately?

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Original NASA ASRS Text

Title: BELIEVING THEY HAD CORRECTED A TRANSIENT HSI ANOMALY DURING PRE-TOF PREPARATION, FLT CREW OF LJ60 DEPART RWY 31C AT MDW IN IMC WHEN THE PROB RECURS. FLT CREW CONCENTRATES ON ANOMALY RELIEF AND BECOME A TFC SEPARATION PROB FOR DEP CTL.

Narrative: PRIOR TO DEP, IN RUN-UP BLOC AT RWY 31C MDW, THE 'HDG' WARNINGS APPEARED IN HSI. DETERMINED THAT COPLT'S HSI WAS THE CAUSE AND 'SLAVED' TO CORRECT HDG. ON TOF ROLL AT APPROX VR (ROTATION) HDG FLAGS AGAIN APPEARED, WITH WHAT APPEARED TO BE 30 DEG SPLIT. MAIN CONCERN DURING THIS PHASE OF FLT WAS TO 'CLEAN' UP ACFT AND CONTINUE WITH DEP 'SID.' HOWEVER, DURING TURN, THE HSI PRECESSION WAS INCREASING. DECIDED TO LEVEL WINGS AND SLAVE GYROS TO ELIMINATE 'HDG' FLAGS WHICH RESULTED IN CORRECT HDG INFO. AT THIS TIME DEP REQUESTED AND RECEIVED AN 'IMMEDIATE R TURN TO 170 DEGS.' A FEW MINS LATER A CLB AND L TURN BAC TO SID PROC WAS ISSUED ALONG WITH A VERBAL DESCRIPTION, BY DEP CTL, OF THE TURN REQUIRED AFTER TOF. BREADOWN OF EVENTS: THE RUN-UP AREA OF RWY 31C AT MDW HAS PREVIOUSLY RESULTED IN COMPARATIVE MONITOR WARNINGS, 'HDG' FLAGS. IS THERE A MAGNETIC ANOMALY AT THIS LOCATION? IT IS ABSOLUTELY MORE IMPORTANT TO 'FLY' THE ACFT AT CRITICAL FLT PHASES AND FIX PREVIOUS PROBS BEFORE CONTINUING INTO MORE COMPLEX FLT ENVIRONMENTS, IE, HVY IFR/TURB/ICING/TSTM AREAS. WHEN AIR TFC CTL OBSERVES AN IMPENDING DEV FROM A PREDETERMINED FLT PATH, SHOULD THEY NOT IMMEDIATELY INQUIRE, RATHER THAN WAIT TO ISSUE CORRECTIVE ACTIONS? SHOULD PLTS INFORM ATC OF WHAT IS PERCEIVED AS A MINOR PROB WITH A QUIC SOLUTION EVERY FLT? IE, FIX PROB OR COMPLY WITH ATC IMMEDIATELY?

Data retrieved from NASA's ASRS site as of July 2007 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.