Narrative:

The situation occurred during an IFR training flight from sql-sac sep/xa/99 at about AB20. WX conditions at sql were 600 ft overcast with the tops of the overcast at 1500 ft. The ATC clearance was, at 400 ft begin a right turn to 120 degrees. As we entered the clouds, the student immediately experienced spatial disorientation and began overbanking. I began instructing the student to shallow the bank at about 30-35 of bank. The student continued to overbank and I took control of the aircraft with a bank angle of approximately 50 degrees. During the steep turn, the directional gyro had precessed about 150 degrees, so when I thought we were on a heading of 120 degrees we were really heading about 270 degrees. The deviation was realized when ATC began querying us as to our heading. It was then I cross-referenced the magnetic compass and realized the error in our heading. I was then given a new heading to fly, and made that turn using the magnetic compass. Then, after I was established on the new heading I reset the directional gyro. There were no more problems during the rest of the flight. As the bank of the aircraft began to increase and I began talking to the student, too much of my attention was focused on the attitude indicator and trying to help the student through the spatial disorientation. I should have focused more on the airplane and not the instructional lesson. Although the directional gyro was within tolerances on the ground, I have noticed more precession of the heading indicator during later flts.

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Original NASA ASRS Text

Title: A CFI RPT REGARDING THE EXCESSIVE PRECESSION OF HIS DIRECTIONAL GYRO AND THE NEAR CFTT NW OF SQL, CA.

Narrative: THE SIT OCCURRED DURING AN IFR TRAINING FLT FROM SQL-SAC SEP/XA/99 AT ABOUT AB20. WX CONDITIONS AT SQL WERE 600 FT OVCST WITH THE TOPS OF THE OVCST AT 1500 FT. THE ATC CLRNC WAS, AT 400 FT BEGIN A R TURN TO 120 DEGS. AS WE ENTERED THE CLOUDS, THE STUDENT IMMEDIATELY EXPERIENCED SPATIAL DISORIENTATION AND BEGAN OVERBANKING. I BEGAN INSTRUCTING THE STUDENT TO SHALLOW THE BANK AT ABOUT 30-35 OF BANK. THE STUDENT CONTINUED TO OVERBANK AND I TOOK CTL OF THE ACFT WITH A BANK ANGLE OF APPROX 50 DEGS. DURING THE STEEP TURN, THE DIRECTIONAL GYRO HAD PRECESSED ABOUT 150 DEGS, SO WHEN I THOUGHT WE WERE ON A HDG OF 120 DEGS WE WERE REALLY HDG ABOUT 270 DEGS. THE DEV WAS REALIZED WHEN ATC BEGAN QUERYING US AS TO OUR HDG. IT WAS THEN I CROSS-REFERENCED THE MAGNETIC COMPASS AND REALIZED THE ERROR IN OUR HDG. I WAS THEN GIVEN A NEW HDG TO FLY, AND MADE THAT TURN USING THE MAGNETIC COMPASS. THEN, AFTER I WAS ESTABLISHED ON THE NEW HDG I RESET THE DIRECTIONAL GYRO. THERE WERE NO MORE PROBS DURING THE REST OF THE FLT. AS THE BANK OF THE ACFT BEGAN TO INCREASE AND I BEGAN TALKING TO THE STUDENT, TOO MUCH OF MY ATTN WAS FOCUSED ON THE ATTITUDE INDICATOR AND TRYING TO HELP THE STUDENT THROUGH THE SPATIAL DISORIENTATION. I SHOULD HAVE FOCUSED MORE ON THE AIRPLANE AND NOT THE INSTRUCTIONAL LESSON. ALTHOUGH THE DIRECTIONAL GYRO WAS WITHIN TOLERANCES ON THE GND, I HAVE NOTICED MORE PRECESSION OF THE HDG INDICATOR DURING LATER FLTS.

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.