Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument
Flight Crew Last 90 Days 150; Flight Crew Type 3600
Communication Breakdown; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Aircraft; Human Factors
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.
C182 instructor pilot reported ATC advised them of a heading deviation that he soon realized was related to a vacuum system malfunction.