Federal regulators have shut down a popular Oahu adventure tour where customers leap from a hovering helicopter into the ocean — bad news for Trident Adventures and thrill-seeking tourists, a win for safety critics.

• The FAA turned down Trident Adventures' request to let passengers unbuckle their seatbelts mid-flight so they can jump into the water.
• Regulators worry about what happens if the engine fails while the helicopter hovers just 10 to 35 feet above the ocean.
• The company argues its training and safety record should count — it has run more than 3,400 jumps without an incident.
• Trident offered to switch to a twin-engine helicopter to reduce the risk of engine failure, but that did not sway the FAA.
• The denial follows a $10,000 state fine in February for unauthorized water drops on Oahu's North Shore, and safety complaints from U.S. Representative Ed Case.

Outlook: Trident is expected to appeal, and aviation experts think it has a reasonable case, but the tours stay grounded in the meantime.