Air Evac EMS Bell 407 accident
Bell 407 · Accident: aircraft structural failure while maneuvering
From San Antonio International Airport (KSAT) to Methodist Hospital Heliport (XS83)
Event
- NTSB case
- CEN16LA027
- 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
- Unknown
- 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
Bell 407
- Aircraft type
- Bell 407
- 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
- N496AE
- Operator
- Air Evac EMS
- Onboard fatalities
- Unknown
- Route
- From San Antonio International Airport (KSAT), San Antonio, TXTo Methodist Hospital Heliport (XS83), San Antonio, TX
- Aircraft age
- About 16 years (built 1999)
- 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
- Maneuvering · hover
- 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
- Aircraft structural failure
- 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
- Aircraft › Aircraft propeller/rotor
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The commercial pilot was conducting an emergency medical services flight. The pilot reported that, when he climbed the helicopter to a 3-ft hover, he heard a loud bang, and the helicopter began an uncommanded right yaw. The pilot applied full left pedal, but this did not arrest the yaw. The pilot then lowered the collective, and the helicopter touched down and then rotated 270 degrees to the right before it came to a stop.
The tail rotor was examined, and it could be manually rotated, but a grinding noise could be heard coming from the damaged No. 3 hanger bearing. The main rotor blades did not rotate in synchronization with the tail rotor blades. The No. 3 tail rotor shaft adapter and shaft splines were completely ground down, the adapter and shaft had failed, and there was evidence of excessive torsion beyond the intended allowable tolerances. The aluminum adapter washer hole was elongated, consistent with a loose through bolt, and the drive shaft through bolt had worn threads. There was a 1/8-inch gap between the adapter and the base of the hanger bearing, consistent with the adapter not being fully in contact with the bearing and potential stress within the adapter and shaft splines. The retaining nut had migrated almost .025 inch outward and was very loose, consistent with the loss of torque, which would have allowed movement between the tail rotor adapter and shaft and led to their eventual failure. A review of the helicopter maintenance manual and operator's approved aircraft inspection program revealed that neither had a requirement for the tail rotor assembly to be inspected for security.
Probable cause
The failure of the No. 3 tail rotor adapter and shaft due to a loss of torque on the retaining nut. Contributing to the accident was the lack of a requirement to inspect the tail rotor assembly for security in the helicopter manufacturer's maintenance manual and the operator's approved aircraft inspection program.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record CEN16LA027
- Event ID
- 20151104X14945
- Case number
- CEN16LA027
- 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: local date, investigation status. Values present in the bulk record are kept.
- The date is the local date; the NTSB stores the UTC date 2015-11-03.
- API snapshot SHA-256: 9e5edc151e1b8d9b2267fe20f2a213449ccbfbfc593849e4404599af712ed37e; retrieved 2026-09-16T02:56:47.092Z.