Summary
We propose to adopt a new airworthiness directive (AD) for all Fokker Services B.V. Model F.28 Mark 1000, 2000, 3000, and 4000 airplanes. This proposed AD was prompted by a design review that revealed insufficient measures were taken to ensure the correct locking of the attachments of the fuel quantity tank units (FQTUs) in each wing tank. When an FQTU becomes loose, this could lead to insufficient clearance between the FQTU and the adjacent tank structure or other metal parts, and under certain conditions, create an ignition source inside the wing fuel vapor space. This proposed AD would require modifying the FQTUs by applying sealant to cover the nuts, washers, and stud ends at the FQTU attachments in each main wing tank. This proposed AD would also require revising the maintenance or inspection program, as applicable, by incorporating a fuel airworthiness limitation item and a critical design configuration control limitation (CDCCL). We are proposing this AD to prevent an ignition source in the wing fuel tank vapor space, which could result in a wing fuel tank explosion and consequent loss of the airplane.