The Story of The Highway Landing Near Bishop

From the e-mail admissions

I had to set my RV-6 down on highway 395 near Bishop Tuesday (January 10, 2006), and here is the story. Mostly things I could have done better, some that I did right or otherwise got lucky. It is an RV6 tip up with a turbocharged Mazda rotary engine.

I took the RV up to Mammoth to ski for the weekend. When I returned to the plane Sunday evening I discovered a small puddle of coolant under the engine. I had some concerns about the cold as my antifreeze had been recently diluted with water when I had to make a field repair of a coolant leak but I neglected to replace the water with antifreeze (big mistake #1). I estimated 25/75 antifreeze/water and the temperatures were supposed to be in the low 20's overnight. This I thought would be enough but I was not sure. The puddle of coolant seemed to prove that overnight the temp got low enough to freeze some coolant and crack something.

A quick look under the cowl failed to reveal the source of the leak other than it was not coming from the previously fixed coolant line or anywhere other than the radiator itself. I didn't have time to trouble shoot, as I had to get home to be at work the next day.

I was able to hitch a ride home in another aircraft, and then drive back up the following evening after work. When I arrived at the airport at 10pm the temperature was 3 deg F. In order to prevent any further damage, I added some anti freeze and ran the engine for a while to circulate it. When I left the airport at 11:30 pm the temperature was -3 deg. This is obviously colder than I had expected and was probably responsible for the damage. The temperature in town was 20 deg despite the fact that town is higher in elevation. The only explanation I have for the extreme low temp at the airport is temperature loss from sublimation of the vast deep snowfields around the airport in the very dry air (just a guess).

I arrived at sun-up the next morning (temp again 4 deg at airport but 19 in town) and got to work on fixing the leak. After several engine runs I determined that the leak was indeed coming from somewhere in the radiator. There did not seem to be any coolant in the oil, but I identified and fixed an oil leak in the turbo oil return line. Also, the engine breather tube (which vents down in the gear leg) had frozen and was causing the turbo to burn oil. That issue was fixed as well.

In order to temporize the radiator leak I decided to use a can of radiator stop-leak and switch coolant to Evan's NPG. NPG is a pure propylene glycol coolant that has a very high boiling temp and can therefore be run with little or no coolant system pressure (I thought lower pressure would further minimize the leak). I switched out the coolant, added the stop-leak, and changed to a 7 psi radiator cap. The stop-leak appeared to do it's job as there was no visible continued leak after an hour of running the engine on the ground at fast idle with some brief runs at higher RPM.

At about 2pm I was cold (temp at the airport now in the mid 20's) and tired (had slept in the car overnight) but decided it was safe to make the flight to Bishop - 27 miles away and 3000 feet lower. There I would remove the cowl and give everything a good look. Since the coolant leak had only lost about a quart in 3 days, was now sealed and would be flown with low pressure I assumed the most I could loose in the 15 min flight would be about a cup of coolant (Big mistake #2?)

The first 8 minutes of flight all systems were green. Then over the course of a minute the coolant temp went up to over 280, oil temp up to over 200 (the highest it has ever been). Being about half-way I decided to continue to the lower Bishop airport. Then the alternator quit (buss voltage dropped to 11.7 and battery showed a discharge). Then oil pressure dropped to zero, followed shortly after by the engine stopping to make power.

It appeared as though I would be able to glide to the Bishop airport. I was at 9000 feet. Bishop was 13 miles away at 4000 feet with no significant winds. I mistakenly assumed there would be an easy dead-stick onto the airport.

I tried to get the prop to stop windmilling by slowing. In my initial flight testing I had been able to stop the prop from windmilling at about 80 kts. However, even by slowing to 65kts IAS I was unable to stop the windmilling. It turns out that overheating the engine had caused the loss of compression on all rotor faces and this prevented me from stopping the windmilling. I was seeing descent rates of 800-1000 fpm at 90 KIAS and it soon became apparent that making the airport would be sketchy at best, so I opted for a quality highway rather than try to overfly the town to make the airfield.

I was able to spot a section of Hwy 395 that was 4-lane divided (no opposing traffic) that also seemed to be free of turns, power lines and intersections. I relayed my situation to the Bishop unicom and got a prompt response. I turned off my fuel pump and in accordance with my training turned off the master power on short final... Doh! I have all electric flight instruments and now had no time to re-boot either of my 2 air speed indicators. (emergency procedures have since been revised)

My plan for traffic avoidance was to come in faster than typical traffic speed, then bleed off that speed at 20 feet over the highway. That way any traffic has plenty of time to see me and slow down while I am bleeding off speed. Touchdown was uneventful and quite a relief. No injury or damage.

The Bishop police were there within minutes, and 2 hours later the plane was tied down at the Bishop airport. I had no time or desire to remove the cowl so the cause is still very unclear. A loss of the accessory belt would explain both the inability to cool and the loss of the alternator, but my bet is still on something to do with the extreme cold and radiator leak. I have to shamefully admit that time pressures were a contributing factor. Feeling the need to return home, I probably rushed the testing process after making repairs. I should have circled Mammoth airport in order to test the repairs at high power before attempting continued flight, especially in mountainous terrain (though there is no freeway in SoCal that would be as forgiving as that section of 395).

I plan to rent some kind of truck next weekend and drive up, remove the wings, and bring the plane home. It will remain in our garage for the next 8 months while I deploy to Iraq. (Suggestions or offers for use of an adequate truck or trailer would be much appreciated). This will also give me a chance to paint the plane and do a lot of the finishing touches that will be easier to do at home than at the airport. Obviously I will need to rebuild the engine as well, but that is a relatively minor issue.

This was quite a learning experience I obviously hope I never have to repeat. All things considered, I feel quite lucky that things turned out so well. Lastly, I want to thank the Bishop Unicom, Police Dept, Highway Patrol, Cal Trans, and Fire Department who were all very professional and helpful. Also, thank you to the fellow RV6 owner was passing by and took an hour and a half out of his day to drive back up to Mammoth and get my car for me.

Update 2010: after retrieving the aircraft and examining the cowl, it was clear that all the coolant had flowed out the overflow bottle. Apparently, the problem was the 7psi radiator cap that I had installed to keep the pressure low. For whatever reason, at full operational temperature and coolant flow the 7psi cap was not nearly enough and the coolant was lost, followed soon after by melting of the rotor housing and complete loss of compression. Also, pressure checking of the radiator failed to show a leak. It is my belief at this time (2010), that I had degraded one of the coolant o-rings (stock madza) from continuously running the engine at temperature above 200F. This allowed combustion gasses to enter the cooling system and force out some of the coolant. The 7psi radiator cap only made the situation worse. One enough of the coolant had been lost the engine got hotter and finished off the coolant gasket. The remaining coolant quickly left and the housings melted.

So I now believe that the underlying cause (compounded by a number of errors on my part) was a cooling system that was less the sufficient and my tolerance of higher coolant temperatures. I no longer believe that the cold temperatures at the airport played a role. I have since dramatically improved the cooling system and have flown over 300 more hours without any cooling issue.

The engine was re-built by me for less than $1500 in parts and supplies.