B-2 crash revives memory of 1990 scandal

It's not unfair to view the first crash of the Northrop Grumman B-2A as a testament to the stealth bomber's admirable safety record.
How many other advanced aircraft designs have avoided a single non-combat related accident after two decades in service? (Nope, I can't think of one either.)
But the crash offers a good excuse to remember one of the B-2's little-known mechanical problems that briefly caused a public scandal for the manufacturer almost 18 years ago, and remains a problem for the bomber fleet even today.
This problem may or may not have played a role in the accident in Guam, but I'm sure it will be checked out by the US Air Force's crash investigators.
The flawed part -- called the actuator remote terminal (ART) -- came to light in 1990. Northrop revealed in its annual report that year that the company was under investigation by the Department of Justice because of the flawed part. A report by The Los Angeles Times, dated April 3, 1990, said:

"The system is called the Actuator Remote Terminal, a device that the Air Force was forced to upgrade while the B-2 has been grounded for modifications since late last year. The ART system has been plagued by severe technical problems, according to an informed source, though the Air Force has denied that the system is not working properly.
The ART plays a critical role in keeping the B-2 stable in flight. It takes commands from the bomber's flight control computer, relays them to flight control surfaces and then provides feedback information to the computer. The B-2, which has an unconventional all-wing design, relies on its computers to maintain stability and without the computers would be unstable."

A year later, USAF officials declared the problem solved. Here's a report from Aerospace Daily in July 1991:

"Maj. Gen. Stephen B. Croker, interviewed by The DAILY in his Pentagon office, said two problems were found in the design of the B-2's fly-by- wire flight control hardware, called the Actuator Remote Terminal System (ARTS), in "the 1987 timeframe," but neither endangered flight crews or renders the B-2 unsafe to fly. Both charges were made in an ABC television program aired Thursday night.
The first problem concerned the fact that "the cooling wasn't adequate in the area of ARTS," and that, presumably, the system would overheat and fail. This was solved by "a redesign...adding cooling vents" to the B-2 airframe in the area of the ARTS, Croker said.
The second problem, more serious, involved the design of a circuit board, which was laid out such that all four redundant ARTS computers relied on a single resistor. A "single point" or "one-path failure" in this part might have had "a cascading effect," disabling the flight controls on one side of the plane and making it unflyable, Croker said. The cascading effect was considered "highly improbable," he added."

Although the problem was "solved" in 1991, the same part was linked to B-2 reliability problems in combat operations nearly eight years. A USAF press release reported on June 11, 1999:

TINKER AIR FORCE BASE, Okla. (AFPN) -- The System Engineering Branch of the B-2 System Program Management Division here has solved a major problem affecting the B-2's mission effectiveness during Operation Allied Force.
In addition, the Tinker Air Force Base, Okla., division cut the flow days from a contracted 45-day turnaround to a two-day turnaround.
The actuator remote terminal, or ART, works the various control surfaces on the B-2. Without it, the wing cannot fly. Because of an airflow-cooling problem, the ART was one of the high-failure items on the B-2 bomber.
"Unlike other aircraft, the B-2 is a fly-by-wire system -- no mechanical interconnects to the flight controls," said Bob Cotton, avionics armament team lead for Oklahoma City B-2 System Program Office. "We send electrical signals from the pilot stick to the actuator remote terminal to the hydraulic actuator, which makes the aircraft perform its various flight maneuvers."
The wing reached a critical point when there was a lack of supply assets for the actuator remote terminal. Rather than cause aborts of combat missions, the B-2 System Program Management Division set out to solve the problem.
"The vendor we were using had a limited capacity for repair," said Cotton. "He was meeting a 23- to 24-day turn around in some instances, but with the increased flying schedule, he was unable to surge his capacity to the point that he could take care of requirements."
Don Ward, flight control avionics equipment specialist, initiated an investigation into how best to repair the actuator remote terminal line replacement units.
A team of engineers from Tinker traveled to Whiteman AFB, Mo., to provide on-the-spot training of ART repair.
The team worked on a compacted schedule around operational mission requirements to accomplish a solution. The sensitive actuator remote terminal has to be set down on a solid granite surface for repairs to ensure leveling. (Courtesy of Air Force Materiel Command News Service)