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Old 14th May 2014, 22:35
  #1868 (permalink)  
Kharon
 
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2008 M18 – ATSB report.

It's not often, these days anyway, to do anything else when CASA of ATSB are mentioned other than doubt the probity or value of anything said or written; but back in 2008, when an M18 had a wing failure, both agencies did a first rate job. It's very satisfying to be able to say that. The curiosity bump was driving me spare, so a drop or two of midnight oil was burned in an attempt to assuage the itch. Started – HERE – (of course) and found this:-

DFE flieger # 35 – "I think this is probably the link you are after wheatbix:

http://www.atsb.gov.au/media/3532975/ao2008084.pdf

It makes reference (Pages 43 to 46 or thereabouts) to the original MTOW of the M18 being 4200kg, and by supplemental amendments and exemptions, increases in MTOW to 4700, then 5300kg, then finally to 6600kg for fire-fighting work. These changes involved reductions in allowable load factors, Vne, Vno and factoring of hours of service, such that 1 hour of flight time would count for more than 1 hour of service life, depending on actual takeoff weights. The report also discusses problems with recordkeeping and tracking of actual takeoff weights, among other issues that could potentially lead to structural problems, and how CASA would act to prevent the problem that occurred in the linked report from recurring."
There are almost 100 pages comprising the excellent, most refreshing ATSB report. Lately I seem to end up 'hunting' for facts and pertinent information; but not this time. The report is well worth reading; of particular interest are the following pages:-

Aircraft modifications - ATSB page 8 (p 18 pdf).
Tests and research – ATSB page 37 (p 47 pdf).
Overweight operations – ATSB page 40 (p 50 pdf).
Aircraft manufacturer-approved overweight operation. ATSB page 41 (p 51 pdf).
CASA general weight exemptions - ATSB page 44 (p 55 pdf).

The following are cherry picked paragraphs from the report:-

During the course of the investigation, it was determined that a number of operators of the aircraft type were not applying the appropriate service life factors to determine the effective hours flown when their aircraft were operated at take-off weights above 4,700 kg. The effect was to overestimate the remaining service life of those aircraft.
It was also found that operators had an interpretation of the Civil Aviation Safety Authority (CASA) exemptions that, by their understanding, permitted operation at weights in excess of the maximum take-off weight and allowed them to operate at higher take-off weights without the need to account for the additional limitation imposed by the manufacturer for operation at those weights.
As a result of the accident, the following safety action has been taken or proposed:
• The operator undertook a retrospective process of applying the service life factors to its aircraft fleet during operations that had involved take-off weights above 4,700 kg and will apply them to all relevant future flights.
• CASA advised that they had contacted Certificate of Registration holders of M18 Dromader aircraft to verify that they had a procedure for recording and factoring aircraft hours that included overweight operations. Further verification would also occur as part of CASA’s routine surveillance program. CASA also advised that they will provide education to operators on the intention of the exemptions and will be revising the exemptions to ensure that the intended interpretation is clear.
The original type-certified aircraft had a 9-cylinder, supercharged, radial engine, developing 967 shaft horsepower. In more recent years, modifications have incorporated more powerful turboprop engines. One such modification, which was approved under United States (US) Federal Aviation Administration (FAA) Supplemental Type Certificate (STC) number SA09039SC, used a Garrett model TPE331 turboprop engine. As a result of the engine change, the modification increased the length of the aircraft’s forward fuselage. After the incorporation of that modification, the aircraft was designated an M18A Dromader (TPE331).
Other modifications to the aircraft included increasing the capacity of the hopper from 2,650 L to 3,028 L, the installation of servo tabs14 to the flight controls, and installation of vortex generators on the wings. The vortex generator manufacturer claimed that the installation resulted in a 7% reduction in the aircraft’s aerodynamic stall speed.
All of the modifications were carried out in accordance with FAA STCs and/or Australian Civil Aviation Regulation (CAR) 35-approved engineering orders.
The upshot seems to be that the modifications made were not some 'back yard bodge up'; not by a long shot. The CASA approach appears to be 'sound' and if it is in error, then it has been on the side of 'reasoned' caution; the CASA operational approval is well supported and (IMO) justified. There was little else, of a practical nature that they could have realistically done. Good job by someone. Once again, most refreshing.

Which only leaves a couple of loose ends, questions if you like. Why is there no engineering data available to support claim of a 'highly dangerous' modification?; the ATSB went to some pains to troll the world looking for similar and came up dry. The AAAA and type operators seem to be a level headed bunch, safety conscious and have a vested interest in preserving life and promoting their services; so I wonder why there are no howls of protest or internal limitations imposed?; if anyone knows and can sensibly evaluate the risks, they can. No; IMO we must look elsewhere for answers this time. Old Akro # 40 makes some sense of the problem.

I just hope the 2014 ATSB report is as good. I think we may have to cut the ATSB and CASA some slack (benefit of doubt) this time, if the 2008 effort is anything to judge by. We'll just have to wait and see; but one would hope the RFS get a sternly worded letter spelling out the authority of the PIC - if the case is proved.

Itch scratched – Endit.

Last edited by Kharon; 14th May 2014 at 23:27. Reason: Beens and peas are good for your heart - the more you eat.
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