Narrative:

After initial climb out to 4000 feet; while being vectored; my student was given a heading of 320; with which we complied. We were then given a heading of 360. Based on our heading indicator; we turned to and were tracking a 360 heading. Moments later; ATC informed us that we had turned too far and to immediately turn back to 360. Since we looked to be on the correct heading; I verified the heading indicator (hi) to the compass; and it was off. I reset the hi; and turned to correct our heading. Again ATC said we were way off and needed to correct. Suspecting a problem; I checked our heading against the compass and the GPS; and reset the hi again; while correcting heading based on the compass and GPS. It became evident that the hi was not working correctly; because each time I tried to set it; it immediately was off again. I informed ATC that we were having a problem with our hi; which I was attempting to resolve. At this point the attitude indicator also began to wander; and it was evident we were having a vacuum system failure. I took control from the student (to avoid a potential unusual attitude and loss of control). ATC contacted us again; and it was evident that I had missed a radio call or two while bringing the plane back under control. I informed ATC that we had a vacuum system failure and requested vectors back to our departure point.ATC then provided us with assistance; and we received no-gyro turns and vectoring back towards our departure point. As soon as we were back in VMC; I cancelled IFR and landed VFR.under similar conditions in the future; I would suspect a vacuum system problem earlier and listened more carefully for ATC calls while troubleshooting.

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Original NASA ASRS Text

Title: C182 instructor pilot reported ATC advised them of a heading deviation that he soon realized was related to a vacuum system malfunction.

Narrative: After initial climb out to 4000 feet; while being vectored; my student was given a heading of 320; with which we complied. We were then given a heading of 360. Based on our heading indicator; we turned to and were tracking a 360 heading. Moments later; ATC informed us that we had turned too far and to immediately turn back to 360. Since we looked to be on the correct heading; I verified the Heading Indicator (HI) to the compass; and it was off. I reset the HI; and turned to correct our heading. Again ATC said we were way off and needed to correct. Suspecting a problem; I checked our heading against the compass and the GPS; and reset the HI again; while correcting heading based on the compass and GPS. It became evident that the HI was not working correctly; because each time I tried to set it; it immediately was off again. I informed ATC that we were having a problem with our HI; which I was attempting to resolve. At this point the attitude indicator also began to wander; and it was evident we were having a vacuum system failure. I took control from the student (to avoid a potential unusual attitude and loss of control). ATC contacted us again; and it was evident that I had missed a radio call or two while bringing the plane back under control. I informed ATC that we had a vacuum system failure and requested vectors back to our departure point.ATC then provided us with assistance; and we received no-gyro turns and vectoring back towards our departure point. As soon as we were back in VMC; I cancelled IFR and landed VFR.Under similar conditions in the future; I would suspect a vacuum system problem earlier and listened more carefully for ATC calls while troubleshooting.

Data retrieved from NASA's ASRS site 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.