On November 17th 2024 we had a few tandems on the schedule in addition to a skydiver training course. At about noon we took off runway 17 with two tandems (4 passengers total). The takeoff was normal, I was making good power and performance. I did my normal left downwind departure to climb to the north of the field. I made about a four mile box and ended up in what can be considered a high downwind at 5000 feet MSL.

The plane was performing well trimmed out to a 90MPH climb. About half way up the field there was a huge drop in power and it got really quite in the cabin. Almost instantly I pushed the nose down to maintain my 90 MPH. My first thought was that I forgot to switch fuel tanks before takeoff and the engine was going to quit. I checked the fuel selector and it was on the left tank like it should. Then, I checked the mags, mixture and engine gauges. To my surprise oil pressure and temperature was normal and my power was constant at 16 in of manifold pressure. This was a huge reduction from the 26 in of manifold pressure that I had set in the climb.

The second big change in the engine instruments was the voltage. The voltage had dropped from 13.8 to 9. This along with the huge power reduction brought me to the conclusion that the super charger belt had broke and took the alternator belt out that was right below it. All of this diagnostics probably took about a min.

In the meantime, the tandem instructors were hooking up their students in preparation to get out. After I figured what happened and confirmed I still could increase power, I let them know. With a brief discussion they decided to stay and land with the plane.

On my decent I contacted ATC and told them what happened. I informed them that we are cancelling jump ops and we are don’t need assistance. I continued in my high downwind to runway 17. After widening my pattern we made a normal landing on 17.

After the incident, we realized there was close to 100 hours on the belt and it failed. We replaced the belt and continued flying that day. We now prevent this from happening by replacing the belt every 50 hours.