WASHINGTON — Boeing has made progress on installing a “safety critical” part across the AH-64 Apache fleet, but it will probably take until at least 2020 for the company to finish the retrofit process, Boeing program officials said Tuesday.

In April, Defense News revealed that the U.S. Army had suspended AH-64E Apache attack helicopter deliveries due to corrosion the service noticed on the aircraft’s strap pack nut, which hold the heavy bolts that attach the rotor blades to the helicopter. The service resumed accepting deliveries on Aug. 31 after Boeing designed a new strap pack nut that will be outfitted on AH-64Es coming off the line.

The company has now retrofitted new strap pack nuts on about 25 percent of the Army’s AH-64D/Es, Kathleen “KJ” Jolivette, director of U.S. Army Services for Boeing Global Services, said during an Oct. 9 roundtable with journalists at the Association for the U.S. Army’s annual conference.

However, Steve Wade, vice president for Boeing attack helicopters, said the fastest the company could move to retrofit the Apache fleet is 2020, saying that “the limiting factor is how fast we can build” retrofit kits.

Boeing’s best-case completion date appears to be at least a full year behind the Army’s own projections. In September, Brig. Gen. Thomas Todd, the service’s program executive officer for aviation, said he expected retrofits of the U.S. Army’s Apache fleet to occur by 2019, with the strap pack nut replacements paid for by the company.

But asked to clarify the upcoming schedule for retrofitting the helicopters, Jolivette declined to detail what was on the books, deferring to the Army.

“They really have the lead; although we’re tightly linked with them, we’re waiting for their direction on what’s next,” she said. “So I really don’t have the timeline. All we know is it’s urgent, it’s important, it is our No. 1 priority today. So we’re at their direction.”

Boeing is also talking with international customers about retrofitting their AH-64Ds and AH-64Es, but so far no foreign Apache has been modified with the new strap pack nut, Jolivette said.

In addition to retrofitting the Apache fleet, Boeing is delivering a temporary fix — a “fail-safe collar” that holds the rotor blades to the rotor in the case that the strap pack nut fails, giving the pilot time to land the helicopter. Those collars do not affect the AH-64’s aerodynamic performance, Wade said.

Collars have been delivered to the U.S. Army for installation across their inventory of 653 AH-64s, but not all international customers have received the collars, Jolivette said.

Wade acknowledged that the program has had a challenging year, but said Boeing was turning a corner and addressing technical issues.

“We’ve worked as partners with our U.S. Army customer, our supply teammates, and our [foreign military sale] and international customers to make sure that we have the right approach for the Apache,” he said. “Our customer is regaining confidence, and we are focused on doing the right thing for the war fighter.”