The ATSB are investigating a fatal accident which occurred last week near the Ulladulla bushfires in southern New South Wales. The M18 Dromader is a single engine aircraft built by the Polish manufacturer Polskie Zakłady Lotnicze (PZL) Mielec, it is used in many countries to fight forest and bushfires, as well as for cropdusting operations. PZL Mielec is Poland’s largest manufacturer of aircraft and the company is owned by Sikorsky, the creator of the famous Black Hawk helicopters used in the United States military.
The Australian Transport Safety Bureau (ATSB) has specifically looked into particular weighting issues with these aircraft following fatal accidents between 2006 and 2011, one of which involved an inflight break up where a nearly 2 metre section of wing separated from the aircraft before the crash. The ATSB safety investigation report, which was released in April 2013, identified several issues with the operation of these aircraft at high take off weight loads. These known issues with the operation of such aircraft will be examined as part of the investigation of this accident.
The crash highlights the danger of firefighting and waterbombing aerial operations, which is recognized in the (draft) Australian Aerial Firefighting Operator’s Manual which says:
Firefighting and related activities are often conducted in challenging flying conditions due to extreme temperatures, strong winds, dissected terrain and poor visibility due to smoke. This hazardous environment may be further compounded by a large number of firebombing and other operational aircraft, both aeroplanes and helicopters, sharing the same airspace. A high level of vigilance and situational awareness is required.According to the National Aerial Firefighting Centre (NAFC) the Civil Aviation Safety Authority (CASA), and the NAFC, together with state and territory fire and land management agencies and the aviation industry have been:
working cooperatively through a number of regulatory and associated issues affecting aerial firefighting in Australia. Some of these issues flow from inconsistencies in regulations and interpretation of regulations, as well as from varying operating practices between state and territory agencies and aircraft operators.The guidance to be set out in the final Operator’s Manual will be beneficial to support continued safety enhancements above and beyond those required under CASA regulations, as it will be informed by those who operate these aircraft each fire season. The draft manual remains open for comment and input.
Update 29 October 2013: The witness reports of a wing separation prior to the crash, together with the fact that such incidents have been known to happen in certain circumstances as reported by the ATSB, are being treated seriously by CASA. Reports have been made that PZL Mielec M18 Dromaders have been temporarily removed from service for inspections following the accident described above.
On 19 October 2000 CASA issued an Airworthiness Directive (AD) in relation to cracking or corrosion of wing attach joints on PZL M18 aircraft following ADs issued by the US Federal Aviation Administration. This followed two instances of inflight wing separations in the US probably caused by severe corrosion which led to higher than normal stress on the wing attachment joints. The CASA AD, which requires repetitive inspections each 500 hours of service or every 12 calendar months by magnetic particle testing, is still in force and therefore represents a continuing requirement for Australian operators of such aircraft.
Update 4 November 2013: The ATSB has conducted an onsite examination of the M18 Dromader aircraft after several days of the crash site being inaccessible due to nearby bushfires. The wings of these aircraft are formed from three large sections each with three attachment points. The onsite examination, as reported in an update on 1 November 2013, confirmed that the left wing had separated at the joint between the outer and centre wing sections, consistent with witness reports. It appears that this happened in an area of pre-existing fatigue cracking in the wing joints (the area of the wings subject to the FAA and CASA ADs described above, which require magnetic particle testing). The wings of the accident aircraft were last examined on 8 August 2013. The investigation will continue after further examination of the particular operator’s wing inspection requirements and methods, and the aircraft’s operation and maintenance history.
Update 2 December 2013: The ATSB today published its Preliminary Report of the ongoing investigation of the inflight breakup and crash of the firefighting M18 Dromader, on 24 October 2013, and which tragically took the life of David Black.
It was revealed, in the report released today, that while the original (3 August 2000) aircraft manufacturer service bulletin in relation to the wing attachments required (only) magnetic particle inspection of the wing attachment fittings, in September, 2000 CASA approved an alternative procedure (eddy-current testing) to the magnetic particle inspection requirement (see Aviation NDT Services QP.00.36(E), Issue 2, dated 8 September 2000). The aircraft in the accident was up to date with respect to inspections under the approved alternative procedure.
The aircraft wing in this situation had separated due to an area of pre-existing fatigue cracking in the “lug lower ligament”. Thus, loads during flight caused the lug to be overstressed detaching the outboard wing section. Such cracks must not have been picked up during the most recent (8 August 2013) eddy-current testing (if any were indeed present at that date).
CASA’s response to the accident initially included grounding all operational M18 aircraft, and requiring operators of such aircraft to provide it with information about whether the AD inspection requirements had been complied with. Since then, on 15 November 2013, CASA amended its AD revoking the approval for eddy-current procedures for wing joint inspections – something the aircraft manufacturer had originally not permitted as a compliant alternate method of inspection. It also added a 100 hourly visual inspection requirement and further “wing off” inspections every 2,500 hours of flight time for these aircraft.
On 22 November 2013 further amended the AD. This amendment required magnetic particle inspection on aircraft which had (in total) less than 2,500 hours of service (ie, newer aircraft). CASA, in the amended AD, has left it open to approve future alternative magnetic particle inspection procedures to that outlined in the aircraft repair manual but, importantly, alternative inspection procedures (to magnetic particle inspection) itself, is no longer anticipated.
The final investigation report is expected by about October 2014. The ATSB has indicated that its continuing investigation will focus on three areas: first, the wing inspection procedures and methods actually used in practice, and second, the particular history of this aircraft’s operations and maintenance.
It is telling that the final area of continuing investigation will examine is the “approval mechanisms for the alternate method of compliance” which implicitly indicates criticism of how and why an alternative to the sensitive and economical magnetic particle inspection method was approved by CASA when the aircraft manufacturer itself did not propose an alternative.
Written by Shine Lawyers. Last modified: January 7, 2020.