# Accident 20230719008919A: Aerospatiale AS-355E TWIN STAR, Farmington, UT, July 19, 2023 - Type: FAA accident report (Accident/Incident Data System), as reported - Date: July 19, 2023, 08:40 local time - Place: Farmington, UT - Damage: Substantial damage - Phase of flight: Landing: Approach - Operating rules: Air taxi and commuter (Part 135) - Operator: TLLA - Location: 41.0300° N, 111.8500° W: From the FAA - Nearby events: https://openairdocs.org/map.md?lat=41.0300&lon=-111.8500&mi=10 - Aircraft: N102UM, registered now (https://openairdocs.org/aircraft/N102UM) (OpenAirDocs) - Registry model: Aerospatiale AS-355E TWIN STAR (registry code 8680805, https://openairdocs.org/model/aerospatiale-as-355e-twin-star) (OpenAirDocs) - Registry engine: Allison 250-C20 series (registry code 03020, https://openairdocs.org/engine/allison-250-c20-series) (OpenAirDocs) - Reported make and model: AEROSPATIALE AS-355E TWIN STAR - Reported engine: ALLISON 250-C20 SER - People aboard: 5 - Fatal injuries: 0 - Other injuries: 0 - Pilot certificates: Commercial pilot, flight instructor - Pilot flight hours: 17,200 total, 2,800 in this make and model, 90 in the last 90 days - NTSB investigation: [NTSB WPR23LA278](https://openairdocs.org/ntsb/WPR23LA278) (OpenAirDocs) - FAA source: FAA Aviation Safety Information Portal (https://asip.faa.gov/) - Page: https://openairdocs.org/incident/20230719008919A ## Narrative As the FAA filed it, in capitals; the FAA replaces private details with ^PRIVACY DATA OMITTED^. THE FLIGHT WAS TO DROP OFF A VEGETATION REMOVAL CREW, WHO WERE CONTRACTED BY ROCKY MOUNTAIN POWER TO REMOVE VEGETATION SURROUNDING POWER LINES. THREE DID NOT SPEAK ENGLISH, SO THE FOURTH TRANSLATED FOR THEM DURING THE PREFLIGHT BRIEFING. THE PILOT HAS NOT WORKED WITH THIS CREW BEFORE. THEY WERE ALL SMALL STATURE, AND THE HELICOPTER FUEL LOAD WAS AT ABOUT 25-28%. HE WAS NOT CONCERNED THAT THE HELICOPTER WAS OVERLOADED; IT WAS WELL BELOW MAX GROSS WEIGHT. THE PILOT DEPARTED FROM THE HOME BASE OF OGDEN, UT THAT MORNING, AND FLEW TO PICKUP THE CREW AT A STANDARD LZ AT THE BASE OF FARMINGTON CANYON, IN THE FOOTHILLS OF THE WASATCH MOUNTAINS. THE PILOT HAS ABOUT 2,800 HOURS OF TOTAL FLIGHT TIME IN THE ACCIDENT HELICOPTER, AND ABOUT 17,000 HOURS TOTAL TIME. THROUGHOUT HIS CAREER HE HAS ENCOUNTERED COUNTLESS ENGINE FAILURES BUT HAS NEVER “BENT METAL”. THE PILOT WAS A DPE FOR THE SLC FSDO FOR 10 YEARS. THE NUMBER 2 ENGINE COMPRESSOR HAD JUST BEEN CHANGED, AND THEY HAD ENCOUNTERED PROBLEMS TRYING TO MATCH THE ENGINES. THE PILOT FOUND IT UNUSUAL THAT THE ENGINE HAD A DIFFERENT TONE THAN ITS REPLACEMENT, AND “HOWLED” LIKE A LAMA HELICOPTER. HE FLEW A SERIES POST-MAINTENCE FLIGHTS AND ENGINE RUNUPS IN THE DAYS LEADING UP TO THE ACCIDENT. THEY HAD ENCOUNTERED PROBLEMS MATCHING ENGINE POWER BETWEEN THE TWO, AND STRUGGLED TO MATCH N1 AND T4, THE PILOT FELT THE NUMBER 2 ENGINE WAS A LITTLE “LAZY”. THROUGH ADJUSTMENT, THEY EVENTUALLY MATCHED THE ENGINES. THE MORNING OF THE ACCIDENT WAS THE FIRST TIME HE HAD FLOWN IT FOR DUTY SINCE THE ENGINE WORK WAS PERFORMED. THE PILOT DEPARTED TO PICK UP THE CREW AND PERFORMED A POWER CHECK, AND ALL WAS GOOD. BOTH ENGINES APPEARED TO PERFORM FLAWLESSLY, SUCH THAT HE SENT A TEXT MESSAGE TO THE MECHANIC SAYING ALL WAS WELL. THE PILOT PICKED UP THE CREW AND BEGAN THE CLIMB TO THE LZ TO DROP THEM OFF, HOWEVER DURING THE CLIMB HE NOTICED THE ROTOR RPM SUDDENLY DROP DOWN TO THE BOTTOM OF THE GREEN ARC. THIS WAS VERY UNUSUAL, BECAUSE THE WEATHER AND LOAD WERE GOOD, AND HE KNEW THERE WAS NO REASON FOR THE POWER TO DROOP BECAUSE THE ENGINE WAS NOWHERE NEAR ITS LIMITS, YET THE PILOT COULD NOT PULL ANY MORE POWER. WITH HINDSIGHT, HE RECOGNIZES THAT HE SHOULD HAVE RETURNED TO BASE, BUT HE HAD ANOTHER JOB TO PERFORM AFTERWARDS AND WAS MISSION FOCUSED. HE BEGAN TO CIRCLE THE HELICOPTER TO CLIMB TO ALTITUDE, AND THEN TURNED TOWARDS THE LZ, WHICH WAS ABOUT 8,000 FT AGL. HOWEVER, AS HE APPROACHED THE LZ THE ROTOR RPM AGAIN DROOPED, AND THE PILOT DECIDED TO BREAK OFF THE APPROACH. HE INITIATED A LEFT TURN SO THAT HE WOULD HAVE MAXIMUM POWER AND TAIL ROTOR AUTHORITY, BUT THE HELICOPTER JUST SUNK INTO THE TREES. THE MAIN ROTOR BLADES STARTED CUTTING TREE LIMBS AND THE ENGINE THEN OVER SPED. WHEN THEY CAME TO REST, HE SHUT DOWN THE ENGINES, APPLIED THE ROTOR BRAKE, AND THEY EGRESSED. THEY STRUCK THE GROUND VERY SOFTLY, AND THE HELICOPTER ROLLED OVER. THE PILOT STATED IT WAS A SOFTER LANDING THAN ANY AUTOROTATION HE HAS EVER PERFORMED. THEY EGRESSED AND THE PILOT PUT OUT A FIRE THAT HAD STARTED IN THE #2 ENGINE EXHAUST DUCT. THE PILOT REITERATED THAT THE HELICOPTER HAD WAY MORE POWER THAN REQUIRED TO LAND, AND THAT BOTH DROOPS WERE HIGHLY UNUSUAL. HE WAS NOT FLYING THE HELICOPTER AT ITS PERFORMANCE LIMITS. ## The NTSB's investigation of this event (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB WPR23LA278](https://openairdocs.org/ntsb/WPR23LA278), Jul 19, 2023: Aerospatiale AS-355E Twin Star (N102UM), Farmington, UT, substantial damage. Probable cause: The premature failure of one of the No. 2 engine compressor bleed valve, which resulted in a partial loss of power to that engine. ## Other reports on N102UM (1) Matched to the same aircraft by N-number and date. - [Incident 19900907056619I](https://openairdocs.org/incident/19900907056619I), Sep 7, 1990: Aerosp AS355E (N102UM), Ann Arbor, MI, Minor damage. Left engine fire warning. Landed. Right engine fire warning. Broken bleed air fitting caused fire. Melted oil jet. From the FAA Accident/Incident Data System. Reports are matched to registry aircraft by N-number and event date, checked against the reported make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. For accidents, the NTSB's own investigation is the fuller record. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.