The plan was for a solo XC from AUS->AQO->LZZ->BMQ->AUS. Total time planned was 3.5 hrs (including FSTB, gassing up, and eating lunch). I think the flight was about 160nm round robin.
Preflight was completely normal, oil was just a tick below 5qt, gas looked fine, instruments were okay, and the mags checked out. The left one dropped just slightly below normal so I leaned out the plane for about a minute (per our procedure) and rechecked it. It tested within the norm the second time.
I departed Austin at 17:51Z (a bit behind schedule, but I was okay with this). Very smooth departure and climb. I even got routed over my property and then Mueller, so I was really enjoying my views. I probably reached my planned altitude of 6,500 just after the towers on Hwy 360. I leaned the mixture out as always, waited for the brief drop in RPM and then a few ticks back to the right. Around this time I was switched over to Houston Center for flight following on 134.20.
Climbing past 5,000 feet on my way to a planned 6,500
Around 18:35Z, just getting over the intersection of HWY 281 in Marble Falls and still at 6,500 feet, I noticed the engine was starting to lose power. I couldn't hear it or feel it, but I saw it on the tach. It was dropping about 100 RPM for 1-2 second every 15-20 seconds or so. I just began monitoring it, and after a minute or so alerted Houston Center to my finding. They asked if I wanted to declare any emergency and I said no, I just wanted to say it in case the problem got worse and I needed more attention. They asked me to keep them updated and business was as usual. The problem persisted.
About 2-5 minutes later the problem got worse and I started noticing the engine dropping about 300 RPM for 1-2 seconds every 15-20 seconds with the 100 RPM drops interspersed between those. I immediately alerted Houston Center to the problem with something to the effect of "Houston Center, Cessna 67796. My engine is definitely having problems now, probably going to have to land". They quickly started giving me very close attention and asking if I had power and such. I replied yes, but that the engine was suffering power losses. At this time we established that I was a student pilot on a solo XC. I had already located a bunch of fields by this time and (as HC noted) Horseshoe Bay was just a few miles off to my west (about my 10 o'clock according to Houston). Though I tried to remain calm, I'm sure they could sense some panic in my voice by this time. Still, I kept doing things as needed and now treated the situation as an emergency, assuming that the engine would die at any moment. I went through the emergency checklist though it didn't seem to fix the 300 RPM drops.
I was still communicating with Houston, treating the situation as an emergency, and the problem was still persisting. I definitely had Horseshoe Bay in my sights, just a few miles off to the west and was just a little below my previous altitude. I informed them that the problem was still continuing and that I would be heading for Horseshoe Bay. Though I had them handy, I requested the runway configuration, airport elevation, and the CTAF. All three were given to me. Just as I started my left turn, and about 1 second before my heart would momentarily stop, the engine lost almost compete power.
I can't be sure, but it dropped down to about 1000? 1200? RPM -- basically just above idle -- and held there for a moment before jumping back up. At this point I told Houston that I had a more severe problem and that the engine was probably about to die. They passed me over to Horseshoe Bay and those guys started bringing me in. They cleared out all other traffic and told me either runway was mine for the taking. I was still around 5,800 feet at this time (PA is 2,100), about 3 miles west of the field, and more or less on a perfect left line for a left downwind to runway 35 (the preferred runway was for 17 but surface wind was only about 3 kts, so I stuck with 35).
I told Horseshoe Bay that I would be making a long extension of my downwind in order to lose my excess altitude. I probably went about twice as far as normal before turning base (doing the best I could to calculate all of the differences quickly in my head). The engine seemed to be working with me at this point, but I was also making a lot of adjustments to it, so hard to know for sure. I turned base still a bit too high, but plenty far out. On final I quickly got down to a good altitude, slowed enough for flaps and added a notch. The other two notches came in at my discretion as I basically was landing by 'feeling it out'.
I put it down on 35 and it was actually a really nice, smooth, and otherwise uneventful landing. Taxiing didn't seem to be much of an issue either. The guy waved me to a spot and was happy to see me. We called Houston Center immediately to let them know, and also Flight Service to alter and close my flight plan.
N47796 on the ground at Horseshoe Bay after my failed engine