[Peetwo]

Chicken and Egg.

As in which came first, is an old, unresolved argument. The case of the missing propeller promises to be along similar lines. Did ‘vibration’ cause the failure or, did the failure of something cause the vibration? Either way, it will take the engineers some time to establish the root cause, forensic investigation, reverse engineering style. It is tough on ‘Rex’ and their passengers to have aircraft out of service; but excellent for the engineers as they have other comparative engines to examine; which have not experienced problems. It would be a bugger if this was a 'one-off'. I don’t know whether FADEC or similar is used, but it’s a fair bet that it is and that information will be priceless.




Time, money, expertise, probity and patience will solve the puzzle.

Update 21/03/17

Via Planetalking... :

REX broke safety rule in last Friday's lost propeller incident
How many times does an airline like REX ignore air safety rules before it is sanctioned?

Ben Sandilands

 
The propeller-less REX flight after landing at Sydney

Opinion It’s time to call ‘bulldust’ on REX’s claims about being ‘abundantly cautious’ in grounding four or five SAAB 340 propjets for inspections following the loss of a propeller off one of a similarly powered aircraft while approaching Sydney Airport last Friday.

If REX had been adhering to safety regulations it would have landed that flight from Albury to Sydney with 16 people on board at Canberra immediately after it had an initial malfunction in that engine.

Instead the crew is now known to have shut down the engine and feathered the propeller after noticing a vibration related problem while close to Canberra and electing to continue all the way to Sydney on one engine at a reduced altitude of 8000 feet until the propeller came off somewhere over the Macarthur area.

IMO it is a little bit early to condemn the flight-crew on deciding to continue past Canberra. There may have been other extenuating circumstances, beyond the pilots control, that precluded Canberra as an alternate option (e.g. WX related issues, operational performance issues etc.)

It could also be that the limited hearsay (Chinese whispers) evidence, could be factually incorrect. Therefore in the interest of trying to verify the PT (or the PT source) version of events I did a search on the flightradar24 site for last Friday's REX Flight ZL768 - click HERE.  

Now if you click on the little graph icon below the time in UTC, then hit play until the trip line reaches the TOPD (from FL170) and hit pause (time 37 minutes & 23 seconds into flight).

Now refer to the top down moving map display. You can see from this that REX ZL768 was well and truly passed Canberra, almost abeam Bowral and probably not too far off their normal TOPD when presumably the flight crew conducted a precautionary engine shutdown and descent to 8000 ft. 

The aircraft then spent approximately 5 minutes maintaining 8000 ft, till at just past 50 minutes a further descent was commenced. This was presumably about the time that the propeller parted company with the aircraft. This could be why the airspeed graphic wildly oscillates for 1 to 2 minutes until a further level off at approximately 4.500 ft.  

Therefore from the time the flight crew shutdown the RH engine till the time the prop departed the aircraft was at least 14 to 15 minutes. This timeframe would appear somewhat at odds with a part of the REX official media release yesterday - see HERE:

The following has been established over the last three days of investigations:

- Following abnormal indications on the right hand engine and in accordance with
checklist procedures, the crew shut down the engine;
- Shutting down the engine also feathers the propeller in order to reduce drag;
- It was at this point that the propeller assembly was seen by the First Officer to separate from its shaft;
- The propeller assembly was seen to rotate upwards and to the right. The
propeller was seen rotating in a horizontal position and then moving away without making contact with the aircraft;
- Both passengers and crew reported that the flight thereafter was smooth and the
landing was normal in spite of bad weather at Sydney with winds exceeding 35
knots;
- All passengers have been contacted and none required further assistance;
- The propeller was found to have sheared off at the shaft and all the fittings at the
main assembly were intact;
- The propeller has not yet been located;
- The Australian Transport Safety Bureau (ATSB) and the Civil Aviation Safety
Authority (CASA) were immediately informed following the event. The ATSB has
despatched a team of investigators to Sydney and the aircraft has been
quarantined;
- Rex has also been in constant communication with the aircraft manufacturer,
Saab and the engine manufacturer, General Electric (GE). The latter has also
kept the National Transportation Safety Board (NTSB) of the United States fully
appraised of the situation and the developments.

 
However other than that slight discrepancy, the REX briefing and recorded chain of events pretty much matches the flightradar24 graphical and moving map display of the REX ZL768 incident flight.


MTF...P2