By Marina Malenic

The F-35 Joint Strike Fighter fleet was grounded last week after a malfunction of one of the test articles, the Pentagon’s F-35 Joint Program Office (JPO) said Friday.

The aircraft, designated AF-4, is one of 10 F-35 System Development and Demonstration (SDD) aircraft. On March 9, AF-4 “experienced a dual generator failure and oil leak while conducting flight test operations” out of Edwards AFB, Calif., JPO spokesman Joe DellaVedova told Defense Daily. The aircraft’s backup system returned it safely to base, according to DellaVedova.

“As a safety precaution, all F-35 flight operations have been temporarily suspended until the root cause of this occurrence is determined,” he said. “Once the cause is known, the appropriate repairs and improvements will be made before flight operations resume.”

Experts from the JPO and prime contractor Lockheed Martin [LMT] were investigating the incident at press time, company spokesman John Kent said via e- mail.

Two F-35 production-model jets–AF-6 and AF-7–flew for the first time in recent weeks (Defense Daily, March 8). The grounding also affects their operations, DellaVedova said.

The two production jets and 10 preproduction test aircraft have completed nearly 700 flights since testing began in December 2006, according to Lockheed Martin.