Prop overspeed. How serious?
The TPE 331, up to a certain production number, had no turbine overspeed protection, which resulted in more catastrophic overspeeds and consequent turbine disintegration when the main gear wheel failed, as it sometimes did, than the manufacturers cared to admit to. Some were on civil public transport aircraft (2 in our fleet alone) and therefore reported, and some were military.
The cure was a modification in the fuel control unit to shut the fuel down if a turbine overspeed was sensed. This was a long time ago, of course, and there would be no engines now flying without the mod. The incident did illustrate the triumph of commercial interests over safety, when the FAA and CAA, having made the said mod mandatory, were persuaded to allow 4 years compliance period, to avoid upsetting all the TPE 331 operators. I don't know how many more exploded in that period. Perhaps none, of course. Perhaps several.
PS I had an overspeeding prop on my first trip in an Aztec A after getting a twin rating on it, with current girlfriend along. A spring broke, or something like that, on the prop lever mechanism, causing it to hit the max RPM stop. I found that if I held the lever in place I could more or less control the RPM, so I did that. I was VFR, ie quite low, over East London heading back to Biggin Hill. Does that count as a proper prop overspeed event? Perhaps not.
The cure was a modification in the fuel control unit to shut the fuel down if a turbine overspeed was sensed. This was a long time ago, of course, and there would be no engines now flying without the mod. The incident did illustrate the triumph of commercial interests over safety, when the FAA and CAA, having made the said mod mandatory, were persuaded to allow 4 years compliance period, to avoid upsetting all the TPE 331 operators. I don't know how many more exploded in that period. Perhaps none, of course. Perhaps several.
PS I had an overspeeding prop on my first trip in an Aztec A after getting a twin rating on it, with current girlfriend along. A spring broke, or something like that, on the prop lever mechanism, causing it to hit the max RPM stop. I found that if I held the lever in place I could more or less control the RPM, so I did that. I was VFR, ie quite low, over East London heading back to Biggin Hill. Does that count as a proper prop overspeed event? Perhaps not.
