What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
(-23) On July 27, 2006 N135KT, a Eurocopter EC135 registered to omniflight helicopters inc. departed North Perry Airport Florida (khwo) on a 14 CFR 135 air ambulance flight at approximately 0845 local time. The pilot stated he departed to the east enroute to key west. At approximately 200-250 feet above ground level (AGL) the rotor RPM segment light illuminated (high side) for 2-3 seconds. He noticed the #1 and #2 needles split with the #1 needle lower and decreasing. The #2 needle was stable. (At the time of the interview the pilot was not sure which system was failing. Later when the pilot sat in the aircraft he confirmed that engine N2 system was the correct gauge he was referencing). The pilot further stated the rotor RPM was high and climbing. He manually took control using the twist grip. This action brought the #1 engine out of fadc and into manual. He stated that he asked the paramedic to verify what caution lights were illuminated. The paramedic verified that "twist grip and engine manual on the #1 side." As he made his turn back to the airport he informed the tower that he intended to return to the airport. The pilot was able to stabilize the aircraft and systems except for the high rotor RPM. Collective was increased as much as possible while maintaining a shallow approach. At approximately 75 feet AGL the helicopter began to shutter and after about one or two seconds the pilot elected to enter an autorotation to the ground. The helicopter landed without incident. The helicopter did continue to shutter throughout the entire landing. At about 50 feet AGL a door popped open due to the vibration. An interview with the air traffic controller on duty stated that the helicopter made a noise as if it were out of track. Several days later technicians found structural damage had occurred due to the over speed. The #1 and #2 engine power turbines were locked up and could not be rotated by hand. The aft engine support to the #1 and #2 engines were bent and distorted due to the rotor over speed. Both engine fadc computers were removed and sent to the manufacturer for data evaluation. The NTSB investigator stated that case would be considered an incident by the NTSB and would not be issued an accident control number.
As the FAA filed it
(-23) ON JULY 27, 2006 N135KT, A EUROCOPTER EC135 REGISTERED TO OMNIFLIGHT HELICOPTERS INC. DEPARTED NORTH PERRY AIRPORT FLORIDA (KHWO) ON A 14 CFR 135 AIR AMBULANCE FLIGHT AT APPROXIMATELY 0845 LOCAL TIME. THE PILOT STATED HE DEPARTED TO THE EAST ENROUTE TO KEY WEST. AT APPROXIMATELY 200-250 FEET ABOVE GROUND LEVEL (AGL) THE ROTOR RPM SEGMENT LIGHT ILLUMINATED (HIGH SIDE) FOR 2-3 SECONDS. HE NOTICED THE #1 AND #2 NEEDLES SPLIT WITH THE #1 NEEDLE LOWER AND DECREASING. THE #2 NEEDLE WAS STABLE. (AT THE TIME OF THE INTERVIEW THE PILOT WAS NOT SURE WHICH SYSTEM WAS FAILING. LATER WHEN THE PILOT SAT IN THE AIRCRAFT HE CONFIRMED THAT ENGINE N2 SYSTEM WAS THE CORRECT GAUGE HE WAS REFERENCING). THE PILOT FURTHER STATED THE ROTOR RPM WAS HIGH AND CLIMBING. HE MANUALLY TOOK CONTROL USING THE TWIST GRIP. THIS ACTION BROUGHT THE #1 ENGINE OUT OF FADC AND INTO MANUAL. HE STATED THAT HE ASKED THE PARAMEDIC TO VERIFY WHAT CAUTION LIGHTS WERE ILLUMINATED. THE PARAMEDIC VERIFIED THAT "TWIST GRIP AND ENGINE MANUAL ON THE #1 SIDE." AS HE MADE HIS TURN BACK TO THE AIRPORT HE INFORMED THE TOWER THAT HE INTENDED TO RETURN TO THE AIRPORT. THE PILOT WAS ABLE TO STABILIZE THE AIRCRAFT AND SYSTEMS EXCEPT FOR THE HIGH ROTOR RPM. COLLECTIVE WAS INCREASED AS MUCH AS POSSIBLE WHILE MAINTAINING A SHALLOW APPROACH. AT APPROXIMATELY 75 FEET AGL THE HELICOPTER BEGAN TO SHUTTER AND AFTER ABOUT ONE OR TWO SECONDS THE PILOT ELECTED TO ENTER AN AUTOROTATION TO THE GROUND. THE HELICOPTER LANDED WITHOUT INCIDENT. THE HELICOPTER DID CONTINUE TO SHUTTER THROUGHOUT THE ENTIRE LANDING. AT ABOUT 50 FEET AGL A DOOR POPPED OPEN DUE TO THE VIBRATION. AN INTERVIEW WITH THE AIR TRAFFIC CONTROLLER ON DUTY STATED THAT THE HELICOPTER MADE A NOISE AS IF IT WERE OUT OF TRACK. SEVERAL DAYS LATER TECHNICIANS FOUND STRUCTURAL DAMAGE HAD OCCURRED DUE TO THE OVER SPEED. THE #1 AND #2 ENGINE POWER TURBINES WERE LOCKED UP AND COULD NOT BE ROTATED BY HAND. THE AFT ENGINE SUPPORT TO THE #1 AND #2 ENGINES WERE BENT AND DISTORTED DUE TO THE ROTOR OVER SPEED. BOTH ENGINE FADC COMPUTERS WERE REMOVED AND SENT TO THE MANUFACTURER FOR DATA EVALUATION. THE NTSB INVESTIGATOR STATED THAT CASE WOULD BE CONSIDERED AN INCIDENT BY THE NTSB AND WOULD NOT BE ISSUED AN ACCIDENT CONTROL NUMBER.