What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Engine failure short final to roof top heliport. Made pad bu hard landing. Rotors chopped off tailboom. (.4)the helicopter lost engine power while on approach to a rooftop helipad, approximately 50 feet high and 50 feet short of the building. The pilot landed the helicopter on the roof, severing the tail boom at the horizontal stabilizer. The safety board conducted a teardown examination of the engine. Disassembly of the gas producer turbine support from the power turbine support revealed a fractured first stage turbine wheel, which displayed a nine airfoil chordal segment of the rim separated from the larger portion of the wheel. According to the allison metallurgist, both the first and second stage turbine wheel blades exhibited evidence of operation of temperatures in excess of 2,200 degrees fahrenheit. Both primary and secondary rim crack fractures exhibited evidence of exposure to extreme temperatures during the engine start sequence. No evidence of engine oil fire was observed on the gas producer turbine components. Chemical analysis of the affected ga s producer turbine components indicted conformance to the specified material types. The allison metallurgist reported that an overtemperature event occurred as a result of a hot start when both wheels were not at operating temperature; an overtemperature event occurring when the engine was at operating temerautres would have melted the first stage turbine wheel blades. The size of the gamma prime at the altered locations indicated the event occurred approximately within the last 10 hours of engine operation. No hot start or overtemperature event was reported to the maintenance facility.
As the FAA filed it
ENGINE FAILURE SHORT FINAL TO ROOF TOP HELIPORT. MADE PAD BU HARD LANDING. ROTORS CHOPPED OFF TAILBOOM. (.4)THE HELICOPTER LOST ENGINE POWER WHILE ON APPROACH TO A ROOFTOP HELIPAD, APPROXIMATELY 50 FEET HIGH AND 50 FEET SHORT OF THE BUILDING. THE PILOT LANDED THE HELICOPTER ON THE ROOF, SEVERING THE TAIL BOOM AT THE HORIZONTAL STABILIZER. THE SAFETY BOARD CONDUCTED A TEARDOWN EXAMINATION OF THE ENGINE. DISASSEMBLY OF THE GAS PRODUCER TURBINE SUPPORT FROM THE POWER TURBINE SUPPORT REVEALED A FRACTURED FIRST STAGE TURBINE WHEEL, WHICH DISPLAYED A NINE AIRFOIL CHORDAL SEGMENT OF THE RIM SEPARATED FROM THE LARGER PORTION OF THE WHEEL. ACCORDING TO THE ALLISON METALLURGIST, BOTH THE FIRST AND SECOND STAGE TURBINE WHEEL BLADES EXHIBITED EVIDENCE OF OPERATION OF TEMPERATURES IN EXCESS OF 2,200 DEGREES FAHRENHEIT. BOTH PRIMARY AND SECONDARY RIM CRACK FRACTURES EXHIBITED EVIDENCE OF EXPOSURE TO EXTREME TEMPERATURES DURING THE ENGINE START SEQUENCE. NO EVIDENCE OF ENGINE OIL FIRE WAS OBSERVED ON THE GAS PRODUCER TURBINE COMPONENTS. CHEMICAL ANALYSIS OF THE AFFECTED GA S PRODUCER TURBINE COMPONENTS INDICTED CONFORMANCE TO THE SPECIFIED MATERIAL TYPES. THE ALLISON METALLURGIST REPORTED THAT AN OVERTEMPERATURE EVENT OCCURRED AS A RESULT OF A HOT START WHEN BOTH WHEELS WERE NOT AT OPERATING TEMPERATURE; AN OVERTEMPERATURE EVENT OCCURRING WHEN THE ENGINE WAS AT OPERATING TEMERAUTRES WOULD HAVE MELTED THE FIRST STAGE TURBINE WHEEL BLADES. THE SIZE OF THE GAMMA PRIME AT THE ALTERED LOCATIONS INDICATED THE EVENT OCCURRED APPROXIMATELY WITHIN THE LAST 10 HOURS OF ENGINE OPERATION. NO HOT START OR OVERTEMPERATURE EVENT WAS REPORTED TO THE MAINTENANCE FACILITY.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.