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.
The ATSB considers that CASA has taken all reasonable steps to alert operators of M18 aircraft of the requirement to correctly calculate and record all flight times that have service life factors applicable to them.
As part of its interim report released on 23 December 2013, the ATSB issued the following Safety Advisory Notice to operators of M18 aircraft:
The Australian Transport Safety Bureau cautions M18 operators of the risks associated with not reliably applying service life factoring to any overweight operations in this aircraft type. It is suggested that operators review the extent to which their aircraft may have been operated above 4,700 kg, and whether the correct service life factoring has been applied to such operations throughout its full operational life.
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.
