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What happened

On 24 October 2013, the pilot of a modified PZL Mielec M18A Dromader, registered VH-TZJ, was conducting a firebombing mission about 37 km west of Ulladulla, New South Wales. On approach to the target point, the left wing separated. The aircraft immediately rolled left and descended, impacting terrain. The aircraft was destroyed and the pilot was fatally injured.

What the ATSB found

The ATSB found that the left wing separated because it had been weakened by a fatigue crack in the left wing lower attachment fitting. The fatigue crack originated at small corrosion pits in the attachment fitting. These pits formed stress concentrations that accelerated the initiation of fatigue cracks.

The ATSB also found that, although required to be removed by the aircraft manufacturer’s instructions, the corrosion pits were not completely removed during previous maintenance. During that maintenance, the wing fittings were inspected using an eddy current inspection method. This inspection method was not approved for that particular inspection and may not have been effective at detecting the crack.

Data from a series of previous flights indicated that the manner in which the aircraft was flown during its life probably accelerated the initiation and growth of the fatigue crack.

Finally, the ATSB also found a number of other factors which, although they did not contribute to the accident, had potential to reduce the safety of operation of PZL M18 and other aircraft. These included the incorrect calculation of the flight time of M18 aircraft and a lack of robust procedures for the approval of non-destructive inspection procedures.

What's been done as a result

The Civil Aviation Safety Authority (CASA) revised the airworthiness directive for inspection of the wing attachment fittings to ensure that they were inspected using the magnetic particle inspection method. CASA also made, or plans to make, a number of changes to their systems and procedures to address issues identified in this report.

Separately, the ATSB reminded operators of M18 aircraft of the importance of the correct application of service life factors when operating at weights above the original maximum take-off weight. In addition, PZL Mielec plans to release additional maintenance documentation clarifying the need for removal of the wings for proper inspection of the wing attachment fittings. Finally, at the request of the owner, the supplemental type certificate for operation of the modified M18 Dromader at take-off weights up to 6,600 kg has been suspended by CASA.

Safety message

This accident shows that even when flying within operational limits, the ‘harder’ and faster an aircraft is flown the more rapidly the structure will fatigue.

To help ensure that maintenance objectives are consistently met, the ATSB reminds aircraft maintenance personnel of the importance of only using properly-approved maintenance instructions. This accident confirms the importance of referring directly to those maintenance instructions when conducting maintenance.

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 Report released 23 December 2013

On 24 October 2013, at about 0940 Eastern Daylight-saving Time, the pilot of a PZL Mielec M18A Dromader, registered VH-TZJ, took off from Nowra Airport to conduct a firebombing mission in the Budawang National Park about 37 km west of Ulladulla, New South Wales. At about 1004, while the aircraft was approaching the target point, the left wing separated. The aircraft immediately rolled left and descended, impacting terrain. The aircraft was destroyed by impact forces and the pilot was fatally injured.

Preliminary examination indicated that the left outboard wing lower attachment lug had fractured through an area of pre-existing fatigue cracking in the lug lower ligament.

This Interim Report was released in order to highlight a safety issue that had been identified after the release of the Preliminary Report on 2 December 2013. The safety issue is that operators of some Australian M18 Dromaders,1 particularly those fitted with turbine engines and enlarged hoppers and those operating under Australian supplemental type certificate (STC) SVA521, have probably conducted flights at weights for which airframe life factoring was required but not applied. The report includes a Safety Advisory Notice to M18 operators about this safety issue.

The first sections of this report are the same as the Preliminary Report released on 2 December 2013. Additional information is contained in the Context (Operation of the M18 Dromader at take‑off weights above 4,200 kg), Safety analysis, and Safety action sections regarding the safety issue.



1     There are three main aircraft variants, the M18, M18A, and M18B, in addition to two-seat trainer versions. Throughout this report, ‘M18’ is used generically to refer to any of the three main variants except where otherwise stated.

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Report released 2 December 2013

The ATSB is investigating the fatal aircraft accident involving a PZL-Mielec M18A Dromader, registered VH-TZJ, that occurred near Ulladulla, NSW at about 1004 on 24 October 2013. The aircraft was being used to conduct firebombing operations and while approaching the target point, the left wing separated. The aircraft immediately rolled left and descended, impacting terrain. The aircraft was destroyed by impact forces and the pilot was fatally injured.
 
Preliminary examination indicated that the left outboard wing lower attachment lug had fractured through an area of pre-existing fatigue cracking in the lug lower ligament.

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The ATSB is investigating the fatal aircraft accident involving a Dromader aircraft that occurred near Ulladulla, NSW on 24 October 2013. The aircraft was being used to conduct aerial work operations when at about 1000 local time, it collided with terrain. The pilot died in the accident.

 


 

 Updated: 1 November 2013

For several days the accident site had been inaccessible due to rugged terrain, high winds, low cloud, and nearby bushfires. On 30 October 2013, due to the efforts of the Rural Fire Service, the NSW National Parks and Wildlife Service, and the NSW Police, a team of five ATSB investigators, including a materials specialist, examined the aircraft wreckage on site (Figure 1).

Figure 1: Part of the accident site

Figure 1: Part of the accident site 

M18 Dromader aircraft have a cantilever wing; that is, it is anchored at one end with no mid-span supports. The wing consists of three sections; the central wing section, and the left and right outer wing sections (Figure 2). Between each outer wing section and the centre section there are three attachment points. At each of the main spar attachment points, a single lug on the outer wing is secured between two lugs on the centre wing by a through bolt and bush (Figure 3).

Figure 2: Overview of wing structure

 Figure 2: Overview of wing structure

Figure 3: Detail of left wing attachment points (centre wing section not shown)

Figure 3: Detail of left wing attachment points

The on-site examination found that the left wing had separated at the joint between the outer wing and the centre wing sections (Figure 4). The ATSB team examined the joints closely to determine the failure mode that resulted in the in-flight separation of the wing. Preliminary examination indicated that the left outer wing lower attachment lug (see arrow in Figure 4 and Figure 5) had fractured through an area of pre-existing fatigue cracking in the lug lower ligament. The fatigue cracking reduced the structural integrity of the fitting to the point where operational loads produced an overstress fracture of the remaining lug material.

Figure 4: Outer section of left wing (under side of wing visible)

Figure 4: Outer section of left wing

Figure 5: Part of failed attachment lug

 Figure 5: Part of failed attachment lug

The ATSB’s on-site examination was completed on 31 October 2013. Several components were removed from the accident site for further examination at the ATSB’s Canberra facilities, including:

  • both sections of the separated lower main spar lug and the remainder of the lower main spar attachment point (left wing)
  • the entire upper main spar attachment point (left wing)
  • part of the rear spar attachment point (left wing)
  • the entire lower main spar attachment point (right wing).

Following M18 Dromader accidents that occurred in the United States involving in-flight wing separation, in September 2000, the United States Federal Aviation Administration issued Airworthiness Directive (AD) 2000‑18-12. This AD required repetitive inspections of the centre wing to outer wing attach joints for ‘cracks in the lugs, corrosion in the main holes, and ovalization of the main holes’. On 19 October 2000, the Australian Civil Aviation Safety Authority (CASA) issued AD/PZL/5 with the same basic inspection requirements.

In accordance with AD/PZL/5, inspections were required every 500 hours time in service or every 12 months, whichever came first. The wings of VH-TZJ were last inspected on 8 August 2013. Up to 17 October, the aircraft had accumulated about 110 hours time in service since the last wing inspection.

As of 24 October 2013, there were 30 M18 aircraft on the CASA aircraft register (including VH-TZJ).

The investigation is continuing and will include examination of the:

  • wing inspection requirements
  • inspection methods
  • history of the aircraft’s operations and maintenance.

It is anticipated that a preliminary investigation report will be released to the public no later than 24 November 2013. Should any critical safety issues emerge in the course of the investigation, the ATSB will immediately bring those issues to the relevant authorities or organisations and publish them as required.

________

The information contained in this web update is released in accordance with section 25 of the Transport Safety Investigation Act 2003 and is derived from the initial investigation of the occurrence. Readers are cautioned that new evidence will become available as the investigation progresses that will enhance the ATSB's understanding of the accident as outlined in this web update. As such, no analysis or findings are included in this update.


 

Updated: 25 October 2013

The ATSB has been unable to gain access to the site of the accident due to the ruggedness of the terrain and an ongoing bushfire risk (Figure 1).

Figure 1: Terrain in the area of the wreckage

 Fig 1: Terrain In the area of the wreckage

However, an initial low-level aerial survey has been carried out to understand the disposition of the wreckage. This showed that the left wing detached in flight (Figure 2), which was consistent with information provided to investigators by a witness to the accident.

Figure 2: Aerial view of the detached left wing (looking at the under surface of the wing)

Fig 2: Aerial view of the detached left wing

 

Further updates will be provided as additional information comes to hand.

 

 

Safety issues

AO-2013-187-SI-02 - AO-2013-187-SI-01 - AO-2013-187-SI-04 - AO-2013-187-SI-03 - AO-2013-187-SI-06 - AO-2013-187-SI-07 - AO-2013-187-SI-08 - AO-2013-187-SI-09 -  

Removal of wings to complete service bulletin actions

Although wing removal was necessary to provide adequate access for effective visual and magnetic particle inspections of M18 wing attachment fittings, the aircraft manufacturer’s service bulletin E/02.170/2000 allowed the wings to remain attached during these inspections.

Safety issue details
Issue number:AO-2013-187-SI-02
Who it affects:Maintainers of M18 aircraft completing CASA AD/PZL/5 and PZL Mielec service bulletin E/02.170/2000
Status:Adequately addressed


 

M18 Dromader airframe life factoring

Operators of some Australian M18 Dromaders, particularly those fitted with turbine engines and enlarged hoppers and those operating under Australian supplemental type certificate (STC) SVA521, have probably conducted flights at weights for which airframe life factoring was required but not applied. The result is that some of these aircraft could be close to or have exceeded their prescribed airframe life, increasing the risk of an in-flight failure of the aircraft’s structure.

Safety issue details
Issue number:AO-2013-187-SI-01
Who it affects:Operators of PZL M18 aircraft
Status:Adequately addressed


 

Spectrum of flight loads

Operation of M18 aircraft with a more severe flight load spectrum results in greater fatigue damage than anticipated by the manufacturer when determining the service life of the M18. If not properly accounted for, the existing service life limit, and particular inspection intervals, may not provide the intended level of safety.

Safety issue details
Issue number:AO-2013-187-SI-04
Who it affects:All operators of M18 aircraft
Status:Adequately addressed


 

Use of eddy current inspection for airworthiness directive AD/PZL/5

The eddy current inspection used on VH-TZJ, and other M18 aircraft, had not been approved by the Civil Aviation Safety Authority as an alternate means of compliance to airworthiness directive AD/PZL/5. This exposed those aircraft to an inspection method that was potentially ineffective at detecting cracks in the wing attachment fittings.

Safety issue details
Issue number:AO-2013-187-SI-03
Who it affects:All operators of M18 aircraft that have had their M18s inspected using the eddy current procedure QP.00.36 (EC)
Status:Adequately addressed


 

Adequacy of the eddy current inspection procedure

The documented procedure for eddy current inspection of M18 wing attachment fittings did not assure repeatable, reliable inspections.

Safety issue details
Issue number:AO-2013-187-SI-06
Who it affects:All operators of M18 aircraft that have had their M18s inspected using eddy current procedure QP.00.36 (EC)
Status:Adequately addressed


 

Civil Aviation Safety Authority records

Important information relating to Civil Aviation Safety Authority (CASA) airworthiness directive AD/PZL/5 was not contained in CASA’s airworthiness directive file, but on other CASA files with no cross-referencing between those files. This impacted CASA’s future ability to reliably discover that information and make appropriately‑informed decisions regarding the airworthiness directive.

Safety issue details
Issue number:AO-2013-187-SI-07
Who it affects:All aircraft operators in Australia
Status:Adequately addressed


 

Assessment of NDT procedures

The Civil Aviation Safety Authority did not have a defined process for a robust, systematic approach to the assessment and approval of alternative non-destructive inspection procedures to ensure that the proposed method provided an equivalent, or better, level of safety than the original procedure.

Safety issue details
Issue number:AO-2013-187-SI-08
Who it affects:All aircraft operators in Australia
Status:Safety action pending


 

Australian supplemental type certificate SVA521

The engineering justification supporting Australian supplemental type certificate SVA521 did not contain consideration of the effect an increase in the average operating speed could have on the rate of fatigue damage accumulation.

Safety issue details
Issue number:AO-2013-187-SI-09
Who it affects:All aircraft operators of the M18 aircraft in Australia operating under STC SVA521
Status:Adequately addressed

 
General details
Date: 24 Oct 2013 Investigation status: Completed 
Time: 1004 EDT Investigation type: Occurrence Investigation 
Location   (show map):37 km west of Ulladulla Occurrence type:In-flight break-up 
State: New South Wales Occurrence class: Operational 
Release date: 15 Feb 2016 Occurrence category: Accident 
Report status: Final Highest injury level: Fatal 
 
Aircraft details
Aircraft manufacturer: PZL Mielec 
Aircraft model: M18A 
Aircraft registration: VH-TZJ 
Serial number: 1Z013-32 
Type of operation: Aerial Work 
Sector: Turboprop 
Damage to aircraft: Destroyed 
 
 
 
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Last update 15 February 2016