Triple M Leasing Eurocopter Deutschland Gmbh MBB-BK 117 C-1 accident
Eurocopter Deutschland Gmbh MBB-BK 117 C-1 · Accident: part(s) separation from aircraft en route
From Penn Presbyterian Medical Center - North Heliport (PA39) to Wings Field (LOM)
Event
- NTSB case
- ERA25LA204
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- Charter & commuter
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Eurocopter Deutschland Gmbh MBB-BK 117 C-1
- Aircraft type
- Eurocopter MBB-BK 117 C-1
- Category
- Helicopter
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N117NC
- Operator
- Triple M Leasing
- Onboard fatalities
- Unknown
- Route
- From Penn Presbyterian Medical Center - North Heliport (PA39), Philadelphia, PATo Wings Field (LOM), Philadelphia, PA
- Aircraft age
- About 28 years (built 1997)
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 135: Air Taxi & Commuter
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- En route · cruise
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Part(s) separation from aircraft
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Personnel issues › Action/decision
- Personnel issues › Task performance
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
The helicopter was returning to its home base following a patient transport mission when it became uncontrollable and began shuddering violently. The pilot experienced a total loss of tail rotor control with no warning. He performed an autorotation, and the helicopter came to rest on a residential lawn. Postaccident examination of the helicopter revealed that the air conditioning louver assembly, tail rotor gearbox, and tail rotor assembly had separated in flight. A recovered louver fragment exhibited contact damage from a tail rotor blade, and both tail rotor blades were destroyed. Examination of the louver’s forward attachment points revealed stripped rivet nuts and evidence of a prior repair; bolts for fastening the louver assembly to the rivet nuts were found within the airframe. Maintenance records indicated that the louver assembly had been removed and reinstalled about 16 flight hours before the accident. Based on the evidence, the rivet nuts for the air conditioning louver assembly were likely stripped during maintenance, resulting in the louver assembly separating from the helicopter in flight and impacting the tail rotor. The tail rotor assembly then separated from the helicopter, which led to a loss of control.
Probable cause
Maintenance personnel’s failure to identify and replace damaged rivet nuts at the air conditioning louver assembly, which resulted in the separation of the louver assembly from the helicopter, the louver assembly’s impact with the tail rotor, and subsequent loss of helicopter control.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ERA25LA204
- Event ID
- 20250520200184
- Case number
- ERA25LA204
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status, coordinates, cause areas. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: c60df3d1d11abec8433769c7a0be459d7c68d5d1bfb0d7c93b466dddbaf51c21; retrieved 2026-09-16T19:53:46.426Z.