As I mostly fly aircraft with fixed-pitch props and in the upper part of their altitude ranges, there is potential risk of engine overspeed. E.g. a Cessna 172S at FL100 turns 2610 rpm at 65% power, redline is 2700. If you set 75%, you get even closer – 2675 rpm at FL80.
So I’ve been wondering what actually happens if you overspeed the engine – both in the sense of potential engine damage and in the sense of necessary engine inspections and possible mandatory maintenance.
The Cessna 172R has the same engine as the 172S (Lycoming IO-360-L2A), but it is derated to 160 hp and limited to 2400 rpm. Does that mean that overspeed up to 2700 could be done without really damaging the engine? Auxiliary equipment could still be damaged, of course.
Typically the propeller is more of an issue for short term overspeeds, and the propeller documentation will give inspection recommendations for a propeller oversped by minor amounts.
Aircraft engines are typically tolerant of going over redline for short periods. Aerobatic aircraft with Lycomings and fixed pitch propellers are (rightly or wrongly) often revved to 3000 rpm in dives for their whole life. A more extreme example is Reno racing Continental O-200s that are typically run to 4200 rpm, more than 50% over redline. They get serviced and inspected between races.
Michal wrote:
for Lycomings check this link -there is an SB to give you an idea.
Thanks! So an accidental overspeed up to 5% doesn’t require any action. Good to know!
I found a more recent version of that SB. Up to 5% still doesn’t require any action except a “recommendation” to record the event in the engine log.
