Crack Caused Curtailed Flight of B-2 Bomber : Air Force Says It Knew of Weakness in Gear Casing

The Air Force said Friday that the mechanical problem that cut short the second test flight of the B-2 Stealth bomber was caused by a crack in a gear drive casing, allowing oil pressure to drop.

The $530-million B-2 was forced to abort its flight Aug. 16 after one hour of a scheduled three- to four-hour flight. A warning light in the cockpit indicated that a low pressure condition had developed in an auxiliary power system, which involved the casing later found to be defective.

The casing was produced by Sundstrand Aviation of Rockford, Ill., which had discovered some time ago that the product was susceptible to cracking and had begun to design a stronger version. However, the original weaker casing is being used on the first two B-2s until the redesigned casing can be made available, an Air Force official said.

Problem Downplayed

“One of the primary things we do on airplanes is save weight, and one of the things you want to do is not put in unnecessary metal thickness that just adds weight,” he said. “They estimated wrong. We had identified that problem earlier in testing and had designed a fix. But the design was such that we could not meet the schedule for the first two airplanes.”

The official added that the problem was considered so minor that if it had occurred on any aircraft other than the controversial and radically designed B-2, the flight would not have been aborted. He said the Air Force would resume testing with the original casings but declined to say when the next flight is scheduled to occur. He said flight testing has not been suspended.

“It doesn’t mean every time you fly it you are going to get a crack,” he said. The crack occurred during a moment of additional stress, though he could not say whether it was related to any specific aerodynamic condition during the flight.

The casing is part of an airframe-mounted auxiliary drive that provides hydraulic and electrical power for the aircraft. There are four of the power units, which are driven by the aircraft’s four jet engines. Each casing is 4 feet long and 1 foot wide.

Indefinitely Suspended

Air Force officials have characterized the problem as minor and said at no time was the crew or aircraft in jeopardy. Any one of the four power drives is capable of supplying all the hydraulic and electrical power needed by the aircraft.

A spokesman at Northrop Corp., the Los Angeles-based prime contractor on the B-2 program, said the company would have no comment on the matter. Northrop is supposed to build 132 B-2s for an estimated $70 billion.

Sundstrand was indefinitely suspended from getting new Pentagon contracts last year and was fined $115 million for overcharging, but the alleged wrongdoing was not connected to the B-2 contract.