Chuck
The PT6 has a mean time between failures of less than 1 failure for every 100,000 hrs flown. If you have had 2 failures of this type of engine than my thought is the engines were not properly maintained. An engine failure because the engine is not properly looked after IMO falls into the preventable enginr failure catagory. As for your comment regarding engine failures in large radial engines...... well I have also shut down big piston engines on numerous occasions due to internal mechanical failures but than it is a different case when you have three other engines still runnning and perfectly able to get you home
However since this is the private aircraft forum I took it as a given that readers would understand that the 80% statistic applies to light aircraft accidents.
However you are correct in that I was insufficently precise in defining where the statistic came from. I got the 80% statistic from Richard Collins (the former editor of flying magazine). He arrived at the statistic after an extensive study of the
light aircraftaccident database in the USA. To be counted in the 80% an aircraft had to have suffered an engine failure and either made an off airfield landing or sustained major damage at touchdown at an airport (mostly EFATO's). Unsurprisingly fuel exhaustion and mismanagement were the most common cause of engine failures and was in virtually every case 100% preventable. Carb ice which had been allowed to develop untill the engine stopped was also a leading cause of light aircraft engine failures. Also included were engines that failed due to a mechanical malfunction but where the fault was evident on the ground and yet the pilot took off anyway. The bottom line was that the majority of engine failures could have been prevented by the pilot.
It would seem that the
least likely scenario for an engine failure in a typical Cessna/Piper light trainer/tourer would be where the a properly maintained engine that had a normal runup, has sufficent uncontaminated fuel, is not icing up and shows normal engine guage indications......suddenly and without warning suffers a total failure. Or in other words the common flight training scenario. This does not mean that the forced approach procedure should not be taught and practiced, just that this scenario is only one possibility among many others and that IMO the best defense against the engine failure emergency is to mimimize the probability of the engine failing in the first place by conducting good runups, carry extra fuel, be vigilient about the formation of carb ice etc etc.