Bell OH-58A N911AF

Summary

On 11 October 2009 at about 00:45 local time, a Bell OH-58A registered N911AF was involved in an accident near Ocala, Florida, United States. 2 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

11 October 2009 at 00:45

Classification

Accident

Location

Ocala, Florida, United States

Nearest airport

Ocala International-Jim Taylor (OCF)

Coordinates

29.1703, -82.2211

Aircraft

Bell OH-58A

Registration

N911AF

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Public Use

Purpose of flight

Public Use

Phase of flight

Not recorded

Route

Ocala → Ocala

Aircraft damage

Substantial

Weather

VMC

Light

Night

NTSB number

ERA10GA015

Nobody was injured.

The excessive wear and failure of engine governor components for undetermined reasons, which resulted in a loss of engine power.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The pilot stated that while on final approach for landing, at about 20 knots and 120 feet above ground level, he felt a "vibration" and the helicopter experienced a loss of engine and rotor rpm. The pilot stated that he lowered the collective for an immediate landing and heard the low-rotor warning horn during the descent. The helicopter experienced a hard landing and rotated to the left after touchdown. Once the helicopter settled, the pilot closed the throttle and exited the helicopter. Initial examination of the helicopter revealed no preimpact mechanical anomalies. The engine was then removed from the helicopter and the turbine governor was removed from the engine. As the turbine governor was removed from the engine, several rolling elements (balls) spilled from the governor and were not recovered. Disassembled portions of the governor were forwarded to the NTSB Materials laboratory and examination of the components revealed the lubricant used was consistent with what was prescribed by the manufacturer. Further examination revealed displacement of the governor driveshaft, deformation of a bearing seal, rotational damage on bearing lands and spacers, as well as spalling on rolling components of the governor. The damage was consistent with wear over an extended period, and neither the cause nor the sequence of wear and failure of the examined components could be determined. Examination of maintenance records revealed that the governor was in service 30 hours beyond its 2,000-hour time-before-overhaul (TBO) interval, but that under the military maintenance program by which the helicopter was maintained, TBO intervals could be adjusted plus or minus 75 hours to align with other scheduled maintenance. Examination of the manufacturer's Operator's Manual revealed that the loss of engine power occurred at an altitude that fell in the "avoid area" of the Height Velocity diagram. According to the manual, “Flight conducted within the avoid area of the chart (figure 9-3) exposes the helicopter to a high probability of damage despite the best efforts of the pilot."

Quoted verbatim from the NTSB record.