Prop Overspeed Multi-Engine

[JonLouis]

This may be too general and not really aircraft specific, but under what circumstances would you NOT feather a prop in an overspeed condition?

[mattyj]

If the other engine has already failed?

[Hugh Jarse]

On the PW12x series, you would not shut down the overspeeding engine if the normal and alternate feather systems do not work.

In that situation, you would slow the aircraft to as slow a speed as is safe, and land at the nearest suitable airport.

Most of us just follow the QRH procedure (which tells you to do all the above).

[muffman]

PW150 is the same as Jarse pointed out.

In a more general sense, depending on how the governor works on the particular propeller, a situation where you are unable to coarsen the blade angle to prevent the overspeed may also create a situation where you can't feather the propeller.

[JonLouis]

Ah alright, thanks for the responses. It really had me puzzled because I was actually watching Ice Pilots Season 1 and the episode with the CL215 prop overspeed I was curious why the engine wasn't feathered. They did feather before landing and did make it fine. I was just trying to run through the situation in my head and how I would deal with something like that. My multi-engine hours are only around 20-25 and in a PA44.

Anyway, thanks for the responses I think I have my answers.

[VH-XXX]

Didn't they say in that episode though that it they feathered it then they would not be able to use it again, so leave it running for now in case? (might have my episodes confused though)

[JonLouis]

They may have said that... I do remember him saying normally he would have feathered but was so weighed down... I was trying to figure out how that would have an effect on the situation. If the prop was causing excess drag + weight he would have dropped quicker I would think. However, if the prop was producing some lift I can see why he didn't shut it down.

[baron_beeza]

As you may have worked out a turbo-prop is going to be much different than a piston twin. Even a free turbine engine may have different procedures from a fixed.

In the case of a piston twin I have seen an instance of an engine over-speed where the prop could then not be feathered. If the pitch control cable breaks the governor spring moves the prop into full fine. The engine instantly over-speeds and slowing the aircraft down is the only way to get things back under control.

As you pointed out the question may be a little too general.
There will be a range of possible answers. The P&W 100 series one is common though.

[JonLouis]

Thanks everyone, I have definitely learned something today.

[T28D]

And even more dramatic in an ASEPTA approved Charter IFR single.

[lemel]

Depends on the aircraft I guess.

I fly a Braz and a prop overspeed is the worst malfunction you could have. The aircraft is uncontrollable and in some cases (in the sim) you can't feather the bloody thing because it is overspeeding so much.

I dare say the air north Braz crash would have had something to do with a prop overspeed.

[Ex FSO GRIFFO]

Hi 'Lemel',

It may be a 'silly' question as I am not endorsed on things like the Braz, but, if you hit the fuel cut-off switch / selector for THAT engine, would the prop slow down eventually, having only the airspeed to keep it rotating??

Cheers

[lemel]

No that wouldn't work because during a prop overspeed its the airflow that is driving the engine. The problem is with the propellers malfunctioning in a low pitch position - shutting down the engine would have no effect on the propeller pitch and the overspeed would remain.

As per the manufacturer/aircraft QRH, the only way to feather the prop in this situation is manually via the condition levers. If this doesn't work, the next option you have is the electrical feather pump which is activated via a switch on the overhead panel when the Np is <120%. This is hard to do when the Np during an overspeed can be in excess of 140%.

[Connaught]

lemel

read the report, air north was a training flight - incidentally training engine failure during takeoff

u CANNOT simulate an engine failure on a braz during takeoff and have the systems work as intended - or any other pw100 as the act of pulling power back disarms the autofeather system

[lemel]

The investigation of the Air North crash is still active and no findings have been released as far as I am aware.

A prop overspeed was what I suspected had occurred (nothing to back it up just pure speculation).

[27/09]

JonLouisMy multi-engine hours are only around 20-25 and in a PA44.

If you had this problem in a piston twin provided you could reduce the RPM to no more than 10% overspeed I would definitely leave the engine running. Any useful power is better than no power at all, plus you still have redundancy with vacuum supply, electrical and possibly hydraulic power.

Ask the pilot who ditched a twin in the Irish Sea a couple of years ago whether or not shutting down the first engine was a smart idea, after feathering a runaway prop she then subsequently suffered a partial power loss on the other engine. Sure there were other considerations here as well, like possible finger trouble and not bothering to consider driftdown to a landing on terra firma.

[Connaught]

apologies for that, i assumed that it would have been closed by now,

wow that takes a while don't it, ?!?!?!?!?!

all i know about that is the company i work for changed alot of training procedures regarding simulating engine failures on take off after that incident

and check this for more speculation

ahttp://www.pprune.org/dg-p-reporting-points/409686-air-north-brasilia-crash-darwin-merged.html

[43Inches]

If you had this problem in a piston twin provided you could reduce the RPM to no more than 10% overspeed I would definitely leave the engine running. Any useful power is better than no power at all, plus you still have redundancy with vacuum supply, electrical and possibly hydraulic power.

This statement is too simple. If the overspeed is caused by oil pressure problems to the hub you may lose your only chance of feathering if you delay. Not all multis feather automatically with loss of oil pressure and if the engine stops rapidly the feather locks may engage prior to it getting to a full feathered position.

The cause and remedy to a propeller overspeed is related to the pitch control mechanism, not necessarily the engine. Many engines have different propeller and hub options which can vary greatly in how they go about their business. How the mechanism operates may be very different for the same engine installation. One prop may have oil pressure one direction with a spring/aerodynamic forces opposing (not so bad if the spring moves it coarse), whilst the next installation has oil pressure moving the blade in both directions (can be very bad if oil is lost without pitch-locks, especially if the prop is capable of reverse pitch). Some may have pitch locks, fixed stops, counterweights, emergency feather pumps/accumulators, engine cut-out limits or no real protection for excessive overspeed.

The point is that you need to know your particular powerplant and how it operates to sucessfully deal with these types of emergencies. Be aware of any unusual indications or operation of the engine that would lead to a sudden overspeed situation and follow the correct aircraft procedure to deal with the situation as early as possible.

[27/09]

43 Inches

You make some good points.

Since the original poster was talking of his/her twin experience (PA44) I was thinking of similar light twins when I wrote my post. What I intended to say but ommitted to do was say that in relation to a light twin like the PA44 I would leave the engine running etc.....

So far as I'm aware my comments are applicable to all or almost all light twins of US origin.

As you say, make sure your systems knowledge is good and act appropriately

[43Inches]

In answer to the original question you would find Pipers answer to be very specific; Don't shut down the engine especially if it can't be feathered.

The Seneca for instance has a statement that if gas pressure to the dome is lost the prop will overspeed and can not be feathered, in this case you would not shut down the engine.

Most light twin manuals will state the initial actions to be followed require reducing power and airspeed to a point the prop will regain within normal limits at the fine pitch stops. They do not recommend shutting down the engine unless the malfunction is an extreme underspeed.

The Procedure from the Seneca manual, it's very generic and pretty similar to most other piper piston twins;

a. Close throttle.
b. Slow aircraft to best rate of climb speed.
c. Pull prop control back to low RPM.
d. Slowly increase throttle until prop governor engaged.
e. Slowly increase power to desired setting.
f. Continue flight at reduced speed and power and land ASAP.

The PA44 adds check oil pressure and maintain IAS and throttle to keep RPM below 2700.

The PA31 has similar advice, including that if you wish to shut down the engine that you should test whether it will feather at idle power.

None of these aircraft manuals recommend shut down or feather during an overspeed.

I think the only cause to shut down an engine in these aircraft after an overspeed would be if there was significant vibration or control issues after reducing power and speed. In most other cases the aircraft should fly within limits at reduced airspeed.