Engine failure after first power reduction
 

We've all been told at some point that engine failure is most likely to happen after the first power reduction. I used to hear it all the time in the piston GA world, and now I'm actually hearing it used in reference to turbofan operations.

Can anyone point me to factual data supporting this argument (for piston or turbine engines), or is this just some myth?

Thanks.

I taught my students that the ovesquare nonsense was just that as well.

I'm looking for that Lycoming flyer you mentioned. The engine failure thing seems to be so ingrained in the GA community in particular that many flight school SOP's are driven by it. I'd really like to have that document handy in the future.

It is, however, a known fact that any engine is more likely to suffer a failure when its running state changes than when steady, hence the experiences that exist where turbines have run without oil for hours until they were throttled up or down when they seized.

Fair point BOAC. If you're changing something, different forces come into play, and things are more likely to go wrong. After hours on end at equilibrium, I can see an argument for that. The argument starts to break down after 1-2 mins at takeoff power though. I'll look into that engine running without oil though. Seems interesting.

Thanks for posting the link. I've spent the last few minutes reading it. Myth busted i suppose.

Dunno 'bout any myth; I'm at 50% right now...

I've had 2 significant (that resulted in power loss and subsequent engine change) compressor stall incidents on the CF6. One was at thrust reduction to climb thrust after takeoff, and the other was 3 hours into a flight at cruise.

"Don'ta toucha nothin'!" is still a good policy at many critical times...

Just to make abundantly clear, I have said NOTHING about the likelihood of an engine failure at take off, but merely given facts from jet operation (not piston as the linked Lycoming document). CA - you need to speak to Rolls Royce - I seem to recall it was an Avon they test ran without oil for many hours until they throttled it back when I think it failed spectacularly. Like Intruder says, if you don't need to, don't touch it! Certainly power change is as Int says, most likely to be the cause of any stall/surges rather than cruise..

Unlike a piston slapper, when you change your power settings on a turbine engine, there's a lot more going on than simply less fuel going into the combustion chamber....there's bleed valves opening/closing, variable inlet guide vanes repositioning, fuel, air and oil pressure changes (many of which are being used as 'muscle fluids' to move other components)....

So while the engine itself may be quite happy with the power change, it only takes one of the supporting actors to step out of line and your power change doesn't go as planned.

Case in point: the BA 777 that almost landed at LHR.

Engine failures occur for vastly different reasons and operating conditions.

A whole bunch of tired turbine parts tend to happen at high power.

A bunch of compressor blade failures happen in early climb

Most of your what-was-that loud explosions happen at high power (takeoff/ early climb) due to part failures.

In the early days of jets (pre 1980s designs) there were many engine stall/surge event noises, without part failures, at power change excursions (Bodies etc.)

Even today if you have a very tired engine compressor (open clearances erroded blades) you will excacerbate the loss in stability just by accel or decel lag between the rotors.

But no I never noticed an overall major standout in flight regime statistics for run-of-the-mill SDR reports for engines.

I was once told that the JT15D-4 engines were also used as pumps, although I don't recall exactly what they were supposed to have pumped.

Anyway, the story goes that these engines were employed to run for a five year non stop service life, with fuel and oil obviously provided throughout.

That's 43,800 hours and one start cycle! Pretty amazing if true.

The PT-6 engine, the turbine section, is used in oil fields as pumps here in the US, they run for years with little or no maintenance.

This is a leftover from the days of big radial engines. There is a lot of highly loaded metal moving around in a big twin/4 row radial and there was plausible evidence that there was more probability of an engine failure at the first power reduction after takeoff than at any other point in the flight. Failures of the engine reduction gearing seem to be a common failure mode.

However for modern piston and turbine engines, I believe no one has been able to demonstrate an increased risk of engine failures at the first power reduction