If they lost lock, or their beam failed, they would be unprotected.

The beams from their flashlights failed to reveal anything significant in the darkness below.

Those few ill-joined beams offered, anyway, a solid surface- a support which elsewhere must have utterly failed us.

The locator beam failed, she thought, and then the crash beacon.

But several other beams failed to hit the second invader, and he lumbered to safety.

A beam may fail due to global or local instability before is reached at any point on its length.

The beam also failed to reach the further shore of the gulf, which might have been many leagues in extent.

After about four minutes its little beam fluttered and failed altogether, and it has never been used again.

However, the dark blue beam failed to hit the M'tachtar, spattering spectacularly on the bulkhead behind the console instead.

Nearby lightning strikes blew out fuses at the farm, while the light beams on the security perimeter failed (twice) without any apparent reason.