An Australian government audit warns that delays in the Lockheed Martin F-35 Joint Strike Fighter programme could keep the Royal Australian Air Force's (RAAF) Boeing F/A-18A/B Hornet aircraft in service beyond 2020.

"[The Department of Defence's] capacity to accommodate any further delays in the production and/or acquisition of the F-35s through a further extension of the life of the F/A-18A/B fleet, beyond the limited extension currently being considered has limits, is likely to be costly, and has implications for capability," says the Australian National Audit Office (ANAO).

In a 160-page report, the ANAO addresses Australia's fighter situation and sustainment issues concerning the RAAF's 71 F/A-18A/Bs and 24 F/A-18F Super Hornets. There was also a 192-page report that dealt with Australia's management of the F-35A acquisition.

The ANAO's audits were based on fieldwork conducted between October 2011 and June 2012. As part of its audit, the ANAO asked the DoD if accommodations were being made for the further delays in the conventional take-off and landing F-35A.

"[The DoD] advised that it will be presenting options to the government later this year on managing the air combat capability, including a limited extension of the planned withdrawal date for the F/A-18A/Bs as the RAAF transitions from the current fleet to a predominantly F-35A fleet."

While the ANAO acknowledges that the DoD has been effective in upgrading the capabilities of its F/A-18A/Bs and mitigating the risks associated with ageing airframes, it cites a number of issues related to prolonging the service life of the type beyond 2020. The aircraft were originally acquired in the late 1980s. The issues include airframe corrosion and fatigue, the need for enhanced safety measures as the F/A-18A/Bs approach the 6,000h safe-limit, and the need to moderately reduce the rate at which the aircraft accumulates structural fatigue.

Although the RAAF's A/B-model Hornets are not likely to surpass 6,000 flight hours until after 2020, the ANAO notes that all but nine of 71 aircraft "have experienced structural fatigue above that expected for the airframe hours flown, leading the [RAAF] to take steps to conserve the remaining fatigue life of its F/A-18A/Bs to ensure they remain operable up to the safe life limit of 6,000 airframe hours."

"Extending the F/A-18A/B fleet's planned withdrawal date beyond 2020 may well require the fleet to undergo an expanded and hence more costly, safety-by-inspection regime, structural modifications programme and capability upgrades," the report says. It notes that between 2001 and 2012, A$1.4 billion ($1.5 billion) was spent on sustaining the type, and that this will rise to A$1.6 billion during 2013-2021.

In May 2012, Australian minister for defence Stephen Smith said the nation will delay its acquisition of an initial batch of 12 F-35As by two years to save costs. Canberra has so far only committed to two F-35As, which will be delivered in the USA and used for ground and aircrew training. It has plans to buy an additional 12 under Project Air 6000 Phase 2A and a subsequent 58 under Phase 2B.

"On the timetable, we have been making sure that we don't end up with a capability gap," Smith said when announcing the delay. "We'll make that decision formally by the end of this year in terms of the capability gap, but my current advice is that the life of our 71 F-18 Classic Hornets and our 24 Super Hornets is sufficient for our air combat capability, but we'll make an advised judgement before the end of this year."

Source: Flight International