Arrow Falcon Exporters OH-58A N902SF

Summary

On 21 January 2012 at about 03:00 local time, a Arrow Falcon Exporters OH-58A registered N902SF, operated by Farm Aviation Inc, was involved in an accident near Brawley, California, United States. One person was 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

21 January 2012 at 03:00

Classification

Accident

Location

Brawley, California, United States

Coordinates

32.9931, -115.5169

Aircraft

Arrow Falcon Exporters OH-58A

Registration

N902SF

Category

Helicopter

Engines

1

Operator

Farm Aviation Inc

Operating rule

Part 137: Agricultural

Purpose of flight

Aerial Application

Phase of flight

Not recorded

Route

Brawley → Brawley

Aircraft damage

Substantial

Weather

VMC

Light

Night

NTSB number

WPR12LA096

Nobody was injured.

The failure of the main rotor mast due to fatigue cracks that originated from corrosion pits. Contributing to the accident was the operator’s failure to adhere to the manufacturer’s recommended overhaul interval for the main rotor mast.

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

Read the full NTSB narrative

During takeoff, the pilot pulled up on the collective, and the main rotor mast fractured near the point where it extends from the transmission; the pilot then aborted the takeoff. The fracture was located below the threads for the mast nut and above the bearing journal for the upper mast bearing. Postaccident examination of the fracture surface revealed multiple fatigue cracks that initiated at the outer diameter of the mast and extended through about 50 percent of the mast's cross section. The fatigue initiation areas and the through-the-wall portion of the fatigue were heavily corroded with extensive pitting and dark deposits visible. A dark oily material was found on the mast's outer surface near the fracture, and the mast's surface was severely corroded on both sides of the fracture. Analysis of samples of the dark oily material suggests that it was a mixture of lubricating oil and water. When the mast is installed on the helicopter, the location where the corrosion and fracture occurred is hidden. To fully inspect the area, the mast assembly must be removed from the helicopter and completely disassembled. Maintenance records indicated that the most recent overhaul of the main rotor mast was completed 2,499 hours before the accident, about 99 hours beyond the helicopter manufacturer's recommended time between overhaul of 2,400 hours. The NTSB has previously investigated a similar main rotor mast failure on the same make and model helicopter; in that case, the most recent overhaul of the main rotor mast was completed 1,486 hours before the accident. As a result of these events, in February 2012, the manufacturer issued an alert service bulletin that reduced the main rotor mast overhaul interval from 2,400 hours to 1,200 hours. Additionally, in July 2012, the Federal Aviation Administration issued Airworthiness Directive (AD) 2012-14-11, applicable to Arrow Falcon Exporters, Rotorcraft Development Corporation, and San Joaquin Helicopters model OH-58A, OH-58A+, and OH-58C helicopters. The AD requires operators of those helicopters to, within 30 days, overhaul the helicopters’ main rotor mast assemblies.

Quoted verbatim from the NTSB record.