The replacement of the fuel tank sealant is only undertaken on the Hercules C-130K aircraft. Flying the aircraft between fuel tank sealant replacement and fitting explosion suppressant foam (ESF) would introduce unacceptable delays to this urgent programme. Therefore, quality assurance processes are used to ensure that it is not necessary to fly the Hercules C-130K aircraft after the fuel tank sealant has been replaced but before ESF is fitted.
The Hercules C-130K explosion suppressant foam (ESF) modification takes approximately 44 days per aircraft to complete. The less complex Hercules C-130J modification takes approximately 16 days. The difference in time scale between the two marks of aircraft is due to the need to replace the fuel tank sealant on the older C-130K. In order to improve overall aircraft availability to the front line command, the ESF modification has been combined with scheduled maintenance wherever possible.