In the process of initial and recurrent training I always try to talk about turbocharger failures and what that means as a whole. It has been a common question posed by clients during initial and recurrent training in piston engine turbocharged airplanes. One common question is how the engine reacts when I lose one turbo (assuming that they have twin turbos). In relaying my turbo failure incident from a couple of summers ago, hopefully I can shed some light on this emergency. Yes I did use the word emergency and I will explain why later.
The day started much like many other days in my flying career. It was a fairly early morning departure from our airport in July a somewhat hazy day, but overall decent weather. Our first stop for the day was to be Atlanta Hartsfield Airport to pick up a passenger who was arriving on the airlines. Because the temperature had dropped that evening and the high humidity/dew point there was some fog at ATL, but as the sun came up I expected it to burn off rather quickly. From our airport to ATL we normally get routed over the Foothills VOR (ODF) V222 LOGEN then direct. It was a typical morning, but due to the fact that we were out flying early we got a little gift from ATC and were cleared direct to LOGEN. We ended up on the ILS because the fog had not cleared yet, but the ceiling was improving as was the visibility. No problem getting into ATL other than the typical request from ATC to keep the speed up followed shortly thereafter by the request to slow down.
After picking up our passenger at ATL we departed for Thomaston, GA. OPN. The weather was not improving quite as quickly at OPN so it would require an instrument approach. The ILS was available so I set up and flew my second ILS of the day. Landed with no problem. In fact I got a little surprise on roll out when I was the DC-3 that I had worked on and recovered the controls for about 10 years earlier.
A few hours later we depart for the reverse of what we had flown earlier. A return flight to ATL and drop off and then a flight back to our home base in Elizabethton, TN. Normally the return trip out of ATL goes something likes this: NELLO, HRS, SOT HMV. This route takes me over the heart of the Smokies, but today it would be different. There were a number of thunderstorms building over that route which would require a route further north toward Knoxville. After getting to the vicinity of Harris VOR I took a more northerly heading toward Knoxville. By the time I had flown just slightly past Knoxville at 17,000 FT. I started my turn back towards 0a9. At this point I had cleared most all of the weather and would have a pretty direct flight back to home, and now I had a descent tailwind and my ground speed had increased. Sometime after passing Knoxville I felt something in my ears. What was that? Looking at the pressurization I realized that I was depressurizing. Check the dump switch and it was where it needed to be. At this point I could feel the airplane slowing and I looked at MAP gauge. I am only making about 13″ MAP. I have a definite problem and need to start a descent. My request went like this, “Atlanta, 75P we are depressurizing and need to start a descent down to one zero thousand.” ATC replies, “Ok 75P turn 20 left you have traffic.”. I guess they did not understand me so I replied, “NO! I am leaving one seven thousand for one zero thousand NOW!” They reply, “OK, so and so airplane turn right 40 degrees.” My thoughts then were why did he not do that in the first place, but Oh well I am descending now. It was not a big panic situation with the aircraft being only at 17,000 ft I was not going to pass out or lose my ability to make decisions for several minutes. I am making a fairly normal descent of 1,000 FPM to 10,0000 ft.
Upon reaching 10,000 ft. my MAP had risen some which told me that I had a problem in keeping the intake manifold pressurized enough to maintain the 30″ MAP setting I had been cruising at. I begin the mental process of deforming my next action. Should I land immediately? By all indications the engine is running smoothly albeit at a much lower power setting. During the descent from 17,000 ft. to 10,000 ft I have chewed up a fair amount of real estate between me and my destination and I am showing about 15 minutes out. I decide that 15 minutes won’t be that bad and I have to lose the 10,000 ft of altitude anyway so by the time I do that in a straight line I be very close to my destination. I am now handed off to Tri-City Approach the facility that controls the airspace around my destination. I opt to stay at 10,000 ft rather than descend just in case I have a problem. A minute or two later I pass Greeneville, TN which is one of the last airports before my destination. Shortly after passing this airport I notice a twitch in the oil pressure needle. The OP is dropping. I inform my passenger of what is going on and now I am getting lined up on about a 10 mile final for RWY 23 but I am at 7,000 ft. I want to keep as much speed as possible in case I have an engine failure, so I do not lower the gear at this point. I am descending at a pretty rapid rate and indicating around 185 KIAS. I get to a point where I know I am going to make the runway and I slow and lower gear. As I am landing the OIL PRESS annunciator is on and the gauge is nearing the bottom. As the wheels touch I pull the mixture and roll into the FBO ramp.
After rolling to a stop we safely exit the aircraft, and I begin my inspection of the aircraft. I am sure that I am going to see oil coming from somewhere, dripping, oozing, or spilling from somewhere underneath the cowling, but there is not sign of oil anywhere. I decide to check the dipstick, and guess what there is no oil on the dipstick either. At this point it becomes very clear to me where the oil went and what happened that caused me to lose pressurization. It must have been a failure of pressure fed bearing in the turbocharger. When the bearing failed the oil must have been burning as it left the exhaust. I do see that the left exhaust is a good bit blacker than the right side. Indeed I had lost the left hand turbocharger. I wonder if it looked like an airshow with the smoke on as I burned nearly 8 quarts of oil through the exhaust in about 10 minutes of flying.
What do I take with me from this situation? I have communicated this several times to my clients since then that if you have a suspected turbo failure the procedure to follow are to land as soon as possible. In my mind at the time I was trouble shooting all the possible failures. It could be an exhaust system failure (without proper exhaust back pressure there is nothing to spin the turbos). It could have been a controller issue or perhaps a wastegate issue. Without knowing though I should have assumed the worst and made an immediate landing. Fortunately for me having taken a more northerly route on this trip I was in a position where I was much closer to several airports. Because of the nature of turbocharger failures it is imperative to treat it like a serious emergency. Don’t hesitate to land at the nearest airport it may save you and the aircraft.