Hercules (C-130)/L100/382
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Flight Instructor
Flight Crew Last 90 Days 18; Flight Crew Total 3800; Flight Crew Type 950
Situational Awareness
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Landing Without Clearance; Ground Incursion Runway
Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Human Factors; Aircraft
I was the Aircraft Commander Pilot in Command (PIC) observing a student instructor pilot provide training to another pilot. We had a dual compass malfunction that led to the crew landing on the wrong runway.En route we noticed a heading error. Our aircraft has two compasses. In the normal position #1 feeds the Pilot HSI and the #2 feeds the Copilot side. Both were malfunctioning but we finally determined that #2 had completely failed; and #1 needed to be adjusted. The compasses are easily adjusted in flight once a known heading is determined. We corrected the heading issue on #1 and switched to where both HSI's were fed from the #1 compass. Our problem appeared to be resolved and we continued the training flight.Over the next 45 minutes to an hour the #1 compass began to slowly drift. During a visual to Runway XY is where we had our issue. Thinking we were set up for Runway XY with confirmation from both pilot and copilot instrumentation (both were selected to the #1 compass) we mistakenly setup for Runway XZ. The pilots called tower requesting touch and go on Runway XY. Tower cleared us 'for the option' on Runway XY. Thinking we were on Runway XY we actually landed on Runway XZ. Shortly after takeoff tower called and asked which runway we were wanting to work on today because they had cleared us for Runway XY; not Runway XZ. At the time we were climbing out on runway heading with both HSI's showing a heading near 250. After some initial confusion we compared the HSI's to the backup magnetic compass and realized what happened.Fortunately we were the only ones training [there] that day; and there were no issues preventing a safe landing on Runway XZ. Tower was willing to give us either runway for touch and go practice; they simply wanted to know which one we were requesting. After we realized the #1 compass was drifting continued to update it on a regular basis. Had it not been a nice VMC day our situation could have been much worse.
C130 Instructor Pilot reported they landed on the wrong runway when they experienced dual compass malfunction.