The Boeing KC-46A tanker’s costs have decreased by $7.3 billion, or about 14%, since its initial estimate but the programme could see future delays, according to a Government Accountability Report released this week.

The US Air Force could decrease its original cost estimate for the KC-46 because the service has not changed requirements and made fewer engineering changes than expected, the GAO report states. That initial estimate included a large amount of risk funding for potential requirement changes.

The total acquisition costs stand at $44.4 billion today, compared to the original cost estimate of $51.7 million in 2011. Development cost estimates have decreased from $7.15 billion in 2011 to $5.9 billion in 2017, a more than 17% reduction. Procurement costs decreased from $40.2 billion to $35,5 billion.

While the KC-46 programme office estimates Boeing will achieve its key and technical performance capabilities, such as completing a mission 92% of the time, significant testing remains, according to the GAO. Potential delays in Federal Aviation Administration certifications and key test events could cause delays in the programme’s delivery schedule.

“Boeing must also complete over 1,700 test points on average for each month from February to September 2017, a level that is more than double what it completed in the last 11 months,” the GAO states. “Programme officials agree that there is risk to Boeing’s test completion rate until it obtains Federal Aviation Administration approval for the design of all parts, including the pods, but test mitigation strategies are underway.”

The GAO determined testing may take longer than the programme office estimates and, if those test points are not completed at the planned rate, the revised delivery schedule is optimistic at best. The Cobham, which makes the KC-46A’s wing aerial refueling pods (WARPs), has not provided all detailed design drawings to the FAA for approval. That could delay electromagnetic effects testing slated to complete this May.

Boeing is also hopeful it can complete 29,000 total developmental flight test points over a 32-month period, a higher rate than the company has previously demonstrated, the GAO states. Boeing must complete those points at the planned rate or risk delivery delays.

The GAO's dour tone does not stray from a January report from the Pentagon’s top weapons tester. If past performance is any indication of future schedules, the Boeing KC-46A Pegasus tanker programme will not go as planned, according to the Pentagon report.

The report also reiterates the KC-46 programme’s delivery schedule slips. Delivery of the initial 18 aircraft is projected for February 2018, rather than the August 2017 date announced last May. The spare engines and WARPS will be delivered in October 2018 as expected.

The WARPS are expected to be the last subsystem to receive design approval, according to the GAO. The programme office estimates the FAA will approve the WARP design by July 2017, allowing Boeing to complete developmental flight tests and achieve key milestones.

“According to Boeing officials, the company and its WARP supplier had underestimated the level of design drawing details the Federal Aviation Administration needed to review to determine that the parts conformed to the approved design,” the report states. "The WARP supplier has been negotiating with its various sub-tier suppliers over the past three years for the necessary design documentation.”