A valve malfunction caused the F-35 grounding order last week. The Honeywell integrated power package (IPP) pulls in outside air to start-up, then switches to engine bleed air after the propulsion system comes online. The valve that switches the flow from inducted to bleed air didn't work, forcing highly compressed air to build up behind the valve until it essentially backfired. Ground tests may resume as early as tomorrow and flight tests could start again next week.
That information comes from Australian journalists who were briefed yesterday in Canberra by Lockheed Martin vice president Tom Burbage. Their news articles have not been posted yet, so there are no links to share.
As of yesterday, the joint programme office in Arlington, Virginia, remained in communications black-out mode.