I didn’t see that (FL175) … no this cannot happen by worn out camshafts, you are right. The engine would not reach max rpm/map either if it couldn’t breathe. Of course the turbochargers are responsible for reaching max power and rpm… so, yes, it might be them …
This 4x fatal accident has some interesting engine data on worn out cam lobes affecting the power. The effect is smaller than one might expect.
I wonder if they ever traced the “maintenance” company and asked them if they ever opened up the oil filter.
That accident report describes a problem (camshaft corrosion/spalling/wear) that I would guess at least 50% of the fleet suffers from. There is no requirement to cut open oil filters and it is very common to not do it (my experience says much less than 50% do it but I have no hard data).
Great experiment done by AAIB and the 10% loss of power is an interesting finding. However, they say it is very easy to detect: your RPM at 100% power during takeoff roll. This only works for a fixed pitch prop and you should look at the RPM at every takeoff and abort should it be lower than what the POH says. One thing they say is not correct:
There is no routine maintenance carried out on the engine that attempts to measure any cam wear, other than an examination of the removed oil filters
There is a SB from Lycoming, upgraded to an AD in EASA land that mandates valve testing every 400h (the “valve wobble test”). This SB also contains instructions how to measure valve travel. I have the fixture to carry out this measurement and it is dead simple.
Yes, 2 of the 4 the turbos did not meet spec and I had to get new ones. One cam shaft didn’t meet spec. She made spec in climb, MP, RPM, everything else. Not only that, she kept cabin pressurised well, which is the first sign of turbo problems. She climbed about 1200ft/min at SL, which is good but not extraordinary for type. They regularly do 1500ft/min. But it’s California and it’s hot, so… However, above 15K feet, the climb rate dropped and at FL175 it was well below 500ft/min. I don’t recall exact numbers right now, but I’d say down to 200-300ft/min. Normally this type should go up to FL250 without much trouble, and even higher (the non-pressurised one is certified to FL300).
However, any pressurised aircraft should be taken to altitude and test flown. It’s very common that they lose steam up there when they have a few hours on the turbos. This being turbo normalised it can be either a turbo problem, a waste gate problem or an induction/airbox problem – or a mix of all the above. There is no TBO for turbos, but if you get 1000hrs out of them, you’ve done well. These were not overhauled. Doesn’t make it unairworthy, though, and no mechanic could fail it for that. If the turbos are not blowing oil, seized or missing bits, they’re airworthy.
