RobertL18C wrote:
Michael is correct, a twin has twice the probability of an engine failure than a single by virtue of having two engines, all things been equal
No, the probability of an engine failure in a twin is less than twice that of a single.
You can see that by assuming that the probability of an engine failure in a single over some time period is 75%. Clearly the probability of an engine failure of a twin over the same period will not be 150%! (It will be ≈94% if we assume that the failures are independent.)
…except they may not be strictly independent, eg fuel contamination
These stats seem to ignore common cause of failure (as well as Robert’s fuel contamination, there is fuel exhaustion, misfuelling, ice blocked inlets, pilot mishandling, engineering failures reproduced across both engines) and Catastrophe Theory (the first failure causes the pilot to put such demands on the second engine that it fails too.)
On the subject of recognition, I have had many, many engine failures on twins and not once, not once, has it presented in the way that it presents in training. Often the nose sways from side to side as the dying engine surges, often the decay is gradual and imperceptible, sometimes the symptoms are almost indistinguishable from the live engine and you end up looking at fuel flow and other parameters.
What that warbird pilot was doing not throttling back the live engine, God only knows. The only answer to an engine failure on the ground (in a non Perf A aircraft) is to kill both engines and take whatever punishment the fence can give you.
Timothy wrote:
On the subject of recognition, I have had many, many engine failures on twins
Isn’t it frightening for a sole person in a single life ? :-)
Wouldn’t that be the experiential confirmation of the double rate of failure on twins ?
Isn’t it frightening for a sole person in a single life ? :-)
Wouldn’t that be the experiential confirmation of the double rate of failure on twins ?
I wonder how many hours Timothy runs his engines to?
I have only had two engine failures which required a precautionary shutdown despite a fair amount of hours on legacy piston twins.
Ironically both shutdowns were on the first flight after overhaul when the prop seal went. Cash flow planning had led me to overhaul one engine before the other, otherwise it would have been a double engine precautionary shutdown – dead stick forced landing in a legacy twin would be testing. Both engines were overhauled when they reached around 20 percent beyond recommended TBO and were using around a quart of oil every four or five hours, otherwise running fine.
On these legacy Twins the Lycomings, especially the normal aspirated variety, are very dependable. Vacuum pumps, alternators, starters, exhaust systems much less so.
Have not had ECU failures on the DA42 but these do occur, however the redundancy should not lead to shutdown.
A friend know to many of us had an overhaul of both engines on a Baron. They managed to put the chrome rings on the steel pistons and the steel rings on the chrome pistons, resulting in all 12 cylinders failing together.
As to Peter’s question about hours, the failures have been spread across a range of engine hours and a wide range of types and maintenance schedules, so I don’t think that that explanation helps.
Oh, and, without checking the figures, I think that the number of failures I have had on singles roughly equates to parity with those on twins.
Off the top of my head, I have had 9 failures on twins and three on singles, and I have about three times as many hours on twins as singles, so no disparity there.
Impressive Timothy !
Engine failure has become a routine !
Are we including “soft” or just speaking about “catastrophic” failures ?
I’ve only had partial engine failure. Was in the old 520. As it happened, I was just about the declare an emergency and land at nearest, but engine “recovered” (after it had spit out it’s two valves and rings and was running on 4 instead of 6, unbeknownst to me), so I elected to continue to my destination as it was only 45mins away. W/X was good, I had plenty of airports around me, engine was stable and showed decent vitals, so it seemed like the right choice. In retrospect, I probably should have landed earlier, as the problem was more severe than I knew at time (I thought a magneto had disintegrated).
I had both my newly overhauled engines on the Aerostar run hot and show low oil pressure on first test flight. Turned out the overhaulers had messed up and not installed under-piston-oil-squirting-nozzle and they both almost seized. Looking back, that was probably the closest I’ve come to a double engine failure. Got her on the ground safely and they had to overhaul the engines again as part of warranty. That was a long wait to add to an already long 6 month wait.
All I can say is, single or twin, I’m really looking forward to turbine reliability. 
