Propellor falls off Rex Saab 340 in NSW Australia
 

Just to hand

Rex aircraft propeller fell off mid flight: Plane forced to land at Sydney airport

I do hope this is not fake news. Nobody seems to have replied and it happened some hours ago.

Thread running here

http://www.pprune.org/australia-new-...dent-yssy.html

No worries, thanks. It's not everyday an aircraft lands sans half a brassiere.

Did you try clicking on the link in the first post ?

http://cdn.newsapi.com.au/image/v1/4...5bb328e2a85d29

Nobody is that good with Photoshop.

It is good to see that major Australian Aviation incidents can be kept on an Australian only forum.

We've been doing it our own way with good results since WW2, so why involve others.

Given the dynamics, 'Saab fall off prop' shurely?

I'm probably going to get in to strife with the moderators, but many Australians, Canadians and people in Asia and South America are concerned about this incident on a Saab 340. It is not just an Australian issue.

More people travel domestically than intercontinental.

A propeller shearing off a domestic flight should be discussed as minutely as a failure of an intercontinental Airbus incident.

This incident is buried in pprune.org

Three pans in play over ten minutes.

http://archive-server.liveatc.net/ys...2017-0030Z.mp3

Initial report from 968, casual as you like, starts around 9:40 mark

Much more serious than first reported.
The Evening Standard says:
:}

Anyway, less drag on the dead side.

amazingly clean break away, unlike a prop blade failure.

Appears to be either a prop shaft break (prop gearbox output shaft), or even failed big retaining nut on the aft side of the "bull" gear internal to the gearbox. There was another lost prop incident in the mid-80s over Lake Erie, US carrier Comair IIRC.

Not first event
 

Previous issue with CT7 gearbox output shaft caused at least 1 starboard propeller departure in flight. Our red on an American Eagle operated Saab 340 in 1991, unlikely to be the identical issue how er?

Correction
 

Apologies operated by Comair departed propeller landed in Lake Erie and disappeared. Fleet inspection was in place at that time.

At least the plane was in a low drag condition for the OEI engine.

More info today

Sydney airline grounds 5 planes after propeller drops off | Miami Herald

I read in one article that the pilot was already taking action on the engine when he saw the prop depart up and over the wing away from the fuselage.

That observation would match a clean release of the prop while still under power.

With a left hand engine it might have been different

From an engineer's point of view this is one of the most disturbing aviation news this year. Here we have a commercial airline in an industrial country, operating a quite common type, following (I suppose) well-audited rules, all the paperwork (supposedly) in order, and we have a major structural failure which had a 50% chance of really messing up the aircraft. Any human error, any aggravating circumstances must have occurred on ground, where they were supposed to be identified and corrected by the supposedly well-audited quality control system. It's just a combination of luck and crew skill the passengers and crew needed no more than counseling (if they even really needed that).


So where's the original problem and what can we learn from the incident?

The report will tell. Should not be too difficult to determine forensically. Fatigue initiated by corrosion pit, tooling mark, could be anything.

http://oi63.tinypic.com/29cxwkg.jpg

Propeller found

http://www.pprune.org/australia-new-...ml#post9713380

swarf =chip detector light/ tooth = sun/planetary disrupt
 

Always best to get a chip-detector light first from the swarf of a lube fail or misalignment. Not good when the sun/planetary enmesh leads to a tooth detaching. That leads to the prop-torque inducing a prop separation. But always good when it detaches cleanly (up, up and away) and doesn't penetrate the fuselage.....

A common cause of fracture failure in a high-quality steel component is a fault in the heat-treatment process, that has led to a finished product that is outside the manufacturers specifications, and which has left the item excessively hardened, or not toughened enough.

In my perusal of the data, that is extremely rare in powerplant related failures.

Such things as gun-drill tool marks, unchamfered oil holes, and quench cracks come to mind.

Barret1 probably has some more in mind

Parallel thread
 

http://www.pprune.org/australia-new-...highlight=saab

And yes, I've seen a raw material defect or two - foreign material inclusions, a forging lap so blatant it failed on the first engine runup, sharp-corner stress riser, crack originating from the p/n marking area. . .

Highly engineered materials that must be properly manufactured, or they are guaranteed to fail!

The discolored section of the shaft does not indicate a sudden, prop-toque induced event...

Prop/fan shafts can fail for a variety of reasons. I recall a fan shaft failure on a nearly new turbofan engine a few years back that was traced to the wrong anti-seize assembly lube being used.
I don't recall the details (and metallurgy isn't exactly my area of expertise), but IIRC the assembly lube promoted stress corrosion on the threads that lead to the shaft failure.

A previous 340 event where the prop was lost, in an identical manner to this, was found to be caused by a slag inclusion in the shaft. DC-10 had a similar event where a fan disc contained inclusions and let go with eye watering results.

A very big difference in (slag-inclusion) detectability between a thin wall shaft and a very thick fan disk both during manufacture and in-service shop visits.

Prelim Report
 

Well here's the prelim report, seems the pprune aib got it more or less right; Investigation: AO-2017-032 - In-flight propeller malfunction involving SAAB 340 VH-NRX, 19 km SW of Sydney Airport, NSW, on 17 March 2017

Indeed

Of note Really curious if they will be able to pinpoint the root cause.

Straight forward metallurgical techniques/examinations. including possible abusive machining. Typically this kind of stuff is batch related and a get well plan already in progress.

No doubt the ATSB or equiv is involved in the precise details of the cause and they will probably close out their invest when satisfied that the regulator has addressed the findings.

Classic helical torsional stress fracture. Will be interesting to see what the underlying cause was.

Sounds like corrosion may be a factor.