In July 2013, prior to the accident involving VH-TZJ, the Civil Aviation Safety Authority (CASA) issued directives to operators of M18 aircraft modified by STC SVA521. The directives required operators to adjust the recorded flight times to account for the applicable factors under the STC.
After receiving notification from the ATSB of the safety issue in December 2013, on 28 October 2014, CASA released Airworthiness Bulletin (AWB) 02-050 to:
highlight to agricultural aircraft operators the importance of ensuring the fatigue lives of any lifed aeronautical product or the aircraft is correctly calculated and recorded.
The AWB recommended that:
…operators who have operated their single engine agricultural aircraft above the certificated maximum take-off weight via any of the CASA exemptions have the airframe life and/or lifed aeronautical products fatigue lives reassessed for those times the aircraft was operated at those higher operating weights.
On 18 February 2015 CASA advised that it had reviewed the records of four Australian M18 aircraft. Of those, three were reportedly not in operation and the fourth was ‘low on hours in relation to the STC and [CASA] concluded there was not a risk of overrun.’
CASA's safety action taken in July 2013 ensured that M18 aircraft operators using STC SVA521 had accounted for operations since the STC was approved. However, this action did not capture operations under exemptions issued by CASA.
Release of AWB 02-050 has now alerted all operators of agricultural aircraft that conduct overweight operations, including operators of M18 aircraft, of the requirement to correctly calculate and record all flight times that attract service life factors.