WASHINGTON (AFNS) — Progress remains steady in the F-35 Lightning II joint strike fighter’s operational testing, reprogramming, fueling, and stand-up training, the F-35 program executive officer told an audience at Aviation Week’s Defense Technologies and Requirements Conference here March 4.

Air Force Lt. Gen. Christopher C. Bogdan said software development is a key factor as the program progresses.

Software is, by its very nature, difficult to develop, the general said, especially when adding to it the complexities of multiplatform fusion, one of the main modification goals for the aircraft.

Even the smallest change to the software can have a big effect, Bogdan said, so repeated testing is required to ensure any software modification works properly.

Interim capability currently allows the F-35s to survey the battle space, absorb information and give the department a clear picture from an individual perspective, the general said. Meanwhile, he added, the software development aims to ensure not only that two jets can assess and fuse the information, but also that multiple systems can share and process the data — systems such as F-22 Raptor fighters, Airborne Warning and Control System aircraft, B-2 bombers, satellites and ground stations.

Bogdan explained that finishing interim capability as quickly as possible with the resources at hand will help the program move to the next development phase. So far, he said, airframe and engine production schedules are stable and predictable, measuring milestones in days and weeks, not months and years.

“It’s more important to know when those lines will come out so we can get them to those bases and start that stand-up,” the general said.

The developmental test program is 50 percent complete for 28 F-35s, Bogdan said. At this time last year, he added, the program office delivered about 36 airplanes, with plans this year to deliver 36 to 38.

“In the next two years, that’ll go up to about 43, and then up into the mid-60s and then three years from now, over a hundred,” the general said. Most of the 58 operational F-35s in the field are in use for training at Eglin Air Force Base, Fla. Operational units are at Marine Corps Air Station Yuma, Ariz.; Nellis Air Force Base, Nev.; and Edwards Air Force Base, Calif.

Affordability continues to be critical, Bogdan said, as officials devise plans to drive costs down in research, development, technology and engineering without requesting any further funds from Congress or the Defense Department. “The enterprise simply cannot tolerate us asking for more money,” he added.

Cost-cutting ideas include an integrated master schedule to synchronize and manage tasks, assess risks assessments, and determine critical paths, the general said. He cited examples including the Marine Corps’ initial operational capability, scheduled for fight testing completion in October and for developmental testing completion in November 2015.

“The [integrated master schedule] has shown us the critical path to both of those events is not software, … but modifications to the airplanes,” Bogdan said. This requires balancing aircraft availability with the need to take jets off the line for modifications.

Progress in a program as complicated as the F-35 requires discipline in the business model, Bogdan said.

“We simply cannot afford to have to do things twice on this program,” he told the conference audience. “We don’t have the time, and we don’t have the money. We know what our commitments are, and we’re going to do everything we can to deliver them.”