FracRisk tool keeps Hercules aloft longer

A new software tool will help enormously with safe fleet life management as these aircraft get older.

A RAAF C-130J Hercules at Avalon International Airshow 2023. The FracRisk tool will help enormously with safe fleet life management as these aircraft get older. Picutre: Department of Defence

The importance to the RAAF of its fleet of C-130J Hercules transport aircraft is evident in the work done by DSTG’s 10-year R&D program resulting in the development of FracRisk.

FracRisk is a software tool developed by DSTG to predict the likelihood of an aircraft incurring fatigue-related structural damage during its next mission.

Last year the tool was transitioned to industry and commercialised by Airbus Australia which carries out C-130J Hercules deep maintenance at RAAF Base Richmond. The RAAF is also now considering applying the FracRisk regimen to its fleet of 24 F/A-18F Super Hornets.

Every air force uses its aircraft in different ways – the longer they use the aircraft, the more those differences matter and the greater the uncertainty around the onset and extent of things like metal fatigue.

And Australia tends to keep its platforms longer, and use them harder, than their manufacturers predict, so good engineering and careful inspections have been the key to keeping the fleet safe. But how often do you need to inspect an aircraft and which bits do you pay close attention to?

FracRisk works by taking data gathered during the manufacturer’s recommended periodic ­inspections as well as from a joint UK-Australia Hercules wing fatigue test by Marshall Aerospace in Cambridge, UK, says Dr Weiping Hu, who leads the discipline of Material Uncertainties and Structural Risks in DSTG’s Platform Division.

The Marshall Aerospace test simulated the stresses and strains and accrual of metal fatigue of a Hercules wing in a series of typical missions. The ADF asked DSTG some ten years ago to analyse the test data because it had recently introduced a new safety regimen, “Safety by Inspection”, and wanted to be certain it was getting the approach right, especially with an ageing aircraft.

The C130J Hercules was a good candidate for the task, says Dr Ribelito Torregosa, an expert in probabilistic risk analysis of aircraft structural failure in DSTG’s Platforms Division and the primary author of FracRisk: lots of inspection data exists from the US, Canadian, UK and Australian Hercules fleets.

The result was what he terms a “probabilistic analysis” of an aircraft’s vulnerability to fatigue damage – assessing the likelihood of something happening, and the consequences; this supplements the existing “deterministic analysis”, based purely on historic data about fatigue and damage, and with little predictive value.

Essentially, the “probabilistic analysis” enables the RAAF’s ­engineers to review assumptions that have underpinned the service’s program of fleet maintenance and inspections. “Safety by Inspection” finally had some hard numbers – some things need inspection more frequently, other things less frequently than originally thought. The RAAF could set its own inspection schedules with confidence its Hercules were safe.

And those schedules can now be changed as aircraft usage changes: high-altitude, straight and level transport work is kind to airframes; low-altitude tactical flying to deliver parachutists or cargoes below an enemy’s radar really stresses an airframe. Doing more of one than the other will change the rate at which the aircraft accrues fatigue.

FracRisk enables fleet managers to predict what a change in the pattern of flight operations will do for individual aircraft, or for an entire fleet. With the prospect of a new Hercules fleet replacing the RAAF’s older C-130Js, FracRisk will help enormously with safe fleet life management as these aircraft get older.

As a measure of how important FracRisk and the C-130J Hercules are to the RAAF, at last month’s Avalon Airshow they were among just six recipients of the Vice Chief of Defence Force’s Capability Award from a field of 170 scientists and engineers nominated for the award.