WASHINGTON — Ruling that airlines have broad immunity from lawsuits under a post-9/11 security law, the Supreme Court on Monday threw out a $1.4 million defamation judgment awarded to a pilot who was reported by his employer as mentally unstable and potentially armed.
The court was unanimous in holding that a law aimed at encouraging reports of possible security threats to the Transportation Security Administration shields airlines from defamation claims when the reports are substantially true.
‘‘Congress wanted to ensure that air carriers and their employees would not hesitate to provide the TSA with information it needed,’’ Justice Sonia Sotomayor wrote for the court. Airlines may be held liable only for recklessly false reports, she said. Full story for BostonGlobe.com subscribers.