# NTSB ATL05LA035: Bell UH-1H, N51AG, Rockford, AL, December 16, 2004

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: December 16, 2004, 16:20 local (22:20 UTC)
- Place: Rockford, AL
- Coordinates: 32.908889, -85.957778
- Nearby events: https://openairdocs.org/map.md?lat=32.9089&lon=-85.9578&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report September 13, 2005
- Report: Approved by Office Director
- Parties: Birmingham FSDO-09
- NTSB case key (mKey): 60748
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ATL05LA035
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/60748/pdf
- Page: https://openairdocs.org/ntsb/ATL05LA035

## Probable cause

The pilot's failure to maintain adequate obstacle clearance, which resulted in an in-flight collision with a tree.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- In flight collision with object, maneuvering - aerial application
  - object - tree(s) (cause)
  - altitude/clearance - not maintained, pilot in command (cause)
  - load jettison
- In flight collision with terrain/water, descent - uncontrolled
  - terrain condition - ground

## Analysis

According to the pilot, during a turn while applying fertilizer over pine trees he heard a "loud bang"; at the same time he lost tail rotor authority. The pilot attempted to level the helicopter and settled into the trees. Post accident examination reveal the helicopter was upright and on its skids. Flight control continuity was established with the cyclic and the collective controls. Examination of the tail rotor blades revealed leading edge damage on both blades. Examination of the helicopter revealed the lower fuselage was buckled and the tail rotor  rear housing of the tail rotor gearbox transmission was broken and cracked. The tail rotor assembly was examined and revealed that the fracture features on the case assembly indicated an overload event. The wear patterns on the teeth of the bevel gears within the gearbox indicated that they were forced apart. There were no indications of any pre-exiting conditions on the components examined that would suggest a failure before the tail rotor strike.

## Factual narrative

On December 16, 2004, at 1620 central standard time, a Bell UH-1, N51AG, registered to and operated by AG Rotors, collided with trees during a spraying operation five miles west of Rockford, Alabama. The agricultural flight was operated under the provisions of Title 14 Part 137 with no flight plan filed. Visual meteorological conditions prevailed at the time of the accident. The pilot was not injured and the helicopter sustained substantial damage. The flight departed from a field site located in the vicinity of Rockford, Alabama, on December 16, 2004, at 1600.

According to the pilot, during a turn while applying fertilizer over pine trees he heard a "loud bang"; at the same time he lost tail rotor authority. The pilot attempted to level the helicopter and settled into the trees.

Post accident examination reveal the helicopter was upright and on its skids. Flight control continuity was established with the cyclic and the collective controls. Examination of the tail rotor blades revealed leading edge damage on both blades. Examination of the helicopter revealed the lower fuselage was buckled and the tail rotor  rear housing of the tail rotor gearbox transmission was broken and cracked. The tail rotor assembly was examined and revealed that the fracture features on the case assembly revealed an overload event. The wear patterns on the teeth of the bevel gears within the gearbox showed that they were forced apart. There was no evident of any pre-exiting condition on the components examined that would suggest a failure before the tail rotor strike.

## Aircraft

- Registration: [N51AG](https://openairdocs.org/aircraft/N51AG), registered now, S/N 71-20178, built 1971 (OpenAirDocs)
- Reported make and model: Bell UH-1H
- Registry model: [Bell UH-1H](https://openairdocs.org/model/bell-uh-1h) (registry code 1181407) (OpenAirDocs)
- Registry engine: [Amateur-built UNKNOWN ENG](https://openairdocs.org/engine/amateur-built-unknown-eng) (registry code 99999) (OpenAirDocs)
- Category: Helicopter
- Damage: Substantial damage
- Flight: Aerial application, Part 137
- Operator: AGRotors Inc.
- Departed: Rockford, AL
- Destination: Rockford, AL

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; injuries: none

## Weather

- Conditions: Visual (VMC)
- Wind: 0° at 0 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 46 °F, dew point 45 °F
- Altimeter: 30.47 inHg
- Observed at: ALX

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.

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