While the manufacturer's instructions for the zonal inspections detailed that installation blankets could be removed 'as necessary', they did not reference the insulation blanket installation procedure. This resulted in insulation blankets not being secured to the structure.
The issue of unsecured insulation blankets has been brought to the attention of Australian operators [Australia is the largest operator of this aircraft type], and operators participated in fleet-wide inspections. The maintainer has implemented documentation to highlight the importance of adequately securing the blankets post maintenance.
Further the manufacturer has amended their procedures and documentation to remove ambiguity and provide clear guidance on the requirements to secure insulation blankets
Fokker Services advised the ATSB, on 23 October 2020, that ‘to avoid uncertainty’ they were ‘undertaking actions’ to add the insulation blanket removal and installation maintenance manual references to the relevant job instruction cards. In addition, the applicable maintenance manual task ‘will be amended to incorporate details of the reason for the reinforcement strips [being] attached to the insulation blankets’. Further, Fokker Services will revise Service Letter 293 ‘to state under which conditions a Part 145 company may fabricate new blankets’.
On 18 December 2020, Fokker Services advised the amended Service Letter would be published by the end of December 2020 and the revisions for the job instruction cards and applicable maintenance procedures will be completed by March 2021. In addition, they plan to issue a Service Engineering Digest article about insulation blankets before the end of the first quarter 2021.
The ATSB welcomes the intended safety action by Fokker Services. Once implemented, it is expected to adequately address the safety issue.
On 1 November 2021 Fokker Services advised that the following actions had been taken to address the safety issue:
The ATSB welcomes the safety action by Fokker Services and considers that it adequately addresses the safety issue.
Fokker Services Asia advised the ATSB that, in addition to their recommendation to Fokker Services for the clarification of maintenance procedures documentation, they also developed a maintenance notice, released on 24 September 2020. This maintenance notice highlighted that, when any task is carried out in the outflow zone area, the insulation blanket is to be inspected for correct manufacture, condition and is to be installed in accordance with the maintenance procedures. Further, this notice was to be attached to the relevant work packs and job instruction cards, until such time as they had been amended.
Network Aviation (Network) conducted a fleet-wide inspection, commencing 12 August 2020, which identified multiple aircraft with incorrectly installed insulation blankets in the outflow area. From this, Network liaised with Fokker Services to establish a temporary installation procedure, including fortnightly inspection, until sufficient spare parts were available for a fleet‑wide replacement of the outflow valve area insulation blankets. Further, Network advised the ATSB that, in addition to the blanket replacement program, their engineers were advised of the importance of following the correct installation procedures.
During the course of the investigation, Virgin Australia and Alliance Airlines had been identified as other operators who had their Fokker 100 aircraft maintained by Fokker Services Asia. Subsequently, on 27 October 2020, and in the interest of transport safety, the ATSB contacted these operators to advise them of the occurrence. In response, both operators advised they were conducting an inspection of their fleet.
On 15 December 2020, Virgin Australia notified the ATSB that their inspection and rectification of their fleet had been completed. In addition, they were implementing a procedure for repeated inspection of the insulation blankets at the outflow valves, at an agreed interval.
On 5 January 2021, Alliance Airlines provided an update to the ATSB. The fleet inspection had identified some insulation blankets as not being correctly installed. Alliance advised they ‘will continue to conduct this fleet inspection until complete’.
The ATSB welcomes the intended safety action by Fokker Services. Once implemented, it is expected to adequately address the safety issue.
