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What happened

In the period 2006 to 2012, the Australian Transport Safety Bureau (ATSB) investigated three fatal accidents involving PZL-Mielec M18 Dromader aircraft. All three investigations identified actual and potential safety issues regarding the operation of M18 Dromader aircraft at take-off weights above 4,200 kg. Although the aircraft were all permitted to operate at increased weights, the ATSB sought an understanding of any common factors across the investigations, and whether there were any implications for the continued safe operation of the type at those increased weights. As a result, the ATSB initiated a safety issues investigation in November 2011 to examine those factors and identify any potential safety issues.

What the ATSB found

The investigation identified several safety issues indirectly arising from the operation of M18 aircraft at increased weights. Though some of these issues were minor in isolation, collectively the increase in risk was more significant and the investigation illustrated the need for careful consideration of potential risks when expanding an aircraft’s role and/or capability.

The investigation established issues regarding the:

  • practicality of a 15° bank angle limitation that is imposed at increased weights, which would probably affect or preclude some agricultural operations,
  • potential for pilots and operators to apply incorrect operating limitations for flights at some weights under a relevant Supplemental Type Certificate (STC),
  • method used to apply service life adjustments required at higher weights,
  • risk of aircraft incorporating the STC not being configured to the same standard as the flight test aircraft, and
  • risk to operators if they do not recalibrate a hopper sight level gauge when changing the hopper size and/or shape.

What has been done as a result

The owner and developer of the STC reported that they were in the process of amending it and were developing a proposal for Civil Aviation Safety Authority consideration and approval. This proposal would address the maximum bank angle limitation and required aircraft modifications, as well as clarify the applicability of the flight manual limitations and airframe service life adjustment method.

Safety message

The investigation highlights some of the risks involved in increasing an aircraft’s operating weight. The importance of pilots and operators understanding and applying any operating limitations that might accompany an operational enhancement is also highlighted.

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Safety issues

AI-2011-150-SI-01 - AI-2011-150-SI-02 - AI-2011-150-SI-03 - AI-2011-150-SI-04 -  

Adherence to M18 flight limitations under Supplemental Type Certificate SVA521

M18 Dromader aircraft were being operated in the agricultural role at weights for which a 15° bank angle limitation had effect, whereas the nature of agricultural operations increased the risk of pilots exceeding that limitation.

Safety issue details
Issue number:AI-2011-150-SI-01
Who it affects:Aerial work industry
Status:Adequately addressed


 

Information for M18 agricultural operations at weights between 4,200 kg and 5,300 kg

There was a potential, depending on the supplements that were incorporated in an aircraft’s flight manual, for pilots and/or operators to apply incorrect operational limitations to agricultural operations in M18 and M18A Dromader aircraft at weights between 4,200 kg and 5,300 kg. This increased the risk of their inconsistent application to these operations, and the likelihood of the unknowing erosion of engineering safety margins and aircraft life.

Safety issue details
Issue number:AI-2011-150-SI-02
Who it affects:Aerial work industry
Status:Adequately addressed


 

Required modifications for M18 aircraft under Supplemental Type Certificate SVA521

There was limited assurance that M18 and M18A Dromader aircraft incorporating Supplemental Type Certificate SVA521 would exhibit acceptable handling and performance characteristics if not fitted with vortex generators and M18B standard elevators, in particular that the risk of longitudinal instability had been reliably addressed.

Safety issue details
Issue number:AI-2011-150-SI-03
Who it affects:Aerial work industry
Status:Adequately addressed


 

Aircraft hopper markings or other level indicators not updated when hopper is modified

Aircraft operations with an enlarged hopper but no associated recalibration of the hopper level sight gauge increased the potential for operations at an uncertain aircraft operating weight, and therefore risk of operations in excess of the published aircraft limitations.

Safety issue details
Issue number:AI-2011-150-SI-04
Who it affects:Aerial work industry
Status:Partially addressed

 
General details
Date: 28 November 2011 Investigation status: Completed 
 Investigation type: Safety Issue Investigation 
Location   (show map):Canberra Office Occurrence type:Miscellaneous - Other 
State: Australian Capital Territory Occurrence class: Technical 
Release date: 09 April 2013 Occurrence category: Other 
Report status: Final  
 
Aircraft details
Aircraft model: M18 Turbine Dromader 
 
 
 
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Last update 01 March 2016