SIKORSKY S-76A PLT HAS A BIRD STRIKE; DECLARES AN EMER; AND RETURNS TO DEP ARPT.

Narrative

WHILE ENRTE TO HOSPITAL FOR AN EMS INTERFAC PATIENT XFER; ACFT HAD A BIRD STRIKE TO THE MAIN ROTOR SYS; WHILE IN CRUISE FLT. ACFT WAS ENRTE FROM ZZZ ARPT TO ZZZ1; NIGHT VFR WITH HIGH LIGHT ILLUMINATION; AT 3250 FT MSL; 135 KIAS; IN CRUISE FLT; WHEN ACFT APPARENTLY HIT A LARGE PREDATORY BIRD SEVERELY DAMAGING ONE MAIN ROTOR BLADE; AND MINOR DAMAGE ON THE HORIZ STABILIZER RESULTING IN LOSS OF R SIDE POS LIGHT ASSEMBLY AND STROBE LIGHT ASSEMBLY. THESE SMALLER COMPONENTS WERE MISSING ON POSTFLT INSPECTION. DURING IMPACT; ACFT SHUDDERED MOMENTARILY AFTER WHAT SOUNDED LIKE A VERY LOUD 'THUMP' DEEP IN THE AIRFRAME. THERE WAS NO NOTICEABLE LOSS OF CTL OR CHANGE IN ROTOR DYNAMICS. AFTER A BRIEF DISCUSSION BY PIC WITH PAX; AS TO THE POSSIBILITIES OF PROBABLE BIRD IMPACT; PIC ELECTED TO ABORT THE MISSION AND RETURN BACK TO ZZZ; THE ARPT OF DEP; WHICH WAS THE NEAREST SUITABLE NIGHT LNDG AREA. RETURN FLT WAS UNEVENTFUL. A POSTFLT INSPECTION REVEALED SIGNIFICANT DAMAGE TO THE STAINLESS STEEL LEADING EDGE OF ONE MAIN ROTOR BLADE; AT APPROX 8 FT FROM THE HUB; 10-12 INCHES WIDE; 1 INCH IN DEPTH. LEADING EDGE WAS DEFORMED AND DE-BONDED; BUT STILL INTACT DESPITE THIS DEFORMATION. PIC BELIEVES THAT THE PROVEN ENGINEERING AND DESIGN WAS SIGNIFICANT IN THE FACT THE BLADE DID NOT DISINTEGRATE ON IMPACT. THERE WAS MINOR DAMAGE TO THE HORIZ STABILIZER ON THE R SIDE; WHICH RESULTED IN A LOSS ON COMPONENTS. THE R SIDE POS LIGHT AND STROBE LIGHT WERE SEPARATED AND DEPARTED ON IMPACT. NO FURTHER DAMAGE WAS NOTED AFTER A THOROUGH POSTFLT AIRFRAME INSPECTION.