Less than two hours into the flight, a warning light came on in the cockpit of Bluebird Six. The indicator, called the Blade Inspection Method, or BIM, warned of a possible leak of the pressurized nitrogen that filled the Sea Stallion's hollow rotors. In the H-53 models the Marines were used to flying, the BIM indicator usually meant a crack in one of the massive blades, which had caused rotor failures and several fatal crashes in the past. As a result, Marine H-53 pilots were trained to land quickly after a BIM warning.
The Navy's RH-53s, however, had newer BIM systems that usually did not foretell a blade failure. To that date, no RH-53 had experienced a blade break and the manufacturer had determined that the helicopter could fly safely for up to 79 hours at reduced speed after a BIM alert.
Down to Seven
However, the pilots of Bluebird Six did not know that. Thinking the craft unsafe to fly, the crew abandoned it in the desert and jumped aboard a helicopter that had landed to help.
The mission was down to seven helicopters.