Bell OH 58A N6251G

Summary

On 2 July 2016 at about 09:30 local time, a Bell OH 58A registered N6251G, 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

2 July 2016 at 09:30

Classification

Accident

Location

Brawley, California, United States

Coordinates

32.9947, -115.5183

Aircraft

Bell OH 58A

Registration

N6251G

Category

Helicopter

Year built

1970

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

WPR16LA134

Nobody was injured.

The engine's degraded performance due to excessive wear of the engine bleed valve, which prevented it from closing during the accident flight. Contributing to the accident was the operator's failure to overhaul the bleed valve within the manufacturer-recommended interval.

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

Read the full NTSB narrative

The commercial pilot reported that, after departing for the agricultural flight, he maneuvered the helicopter to line up with the field to be sprayed. Shortly after lining up with the field, the engine started to surge, and he saw the torque meter needle "bouncing rapidly." The pilot initiated a precautionary landing to an open field. The helicopter landed hard, which resulted in substantial damage to the tailboom and tail rotor drive shaft. A test run of the engine revealed that the bleed valve did not close at any speed and that the engine produced less than 250 horsepower (hp). The bleed valve was disassembled, and the diaphragm was found to have several holes and cracks, and the poppet valve located in the bleed valve assembly had radial play, consistent with worn bushings. The damaged bleed valve was replaced with an overhauled bleed valve, and during a subsequent test run, the engine produced about 380 hp, which is about 7% below minimum allowable power for a serviceable engine. Given these results, the excessive wear of the bleed valve likely prevented it from closing during the accident flight, which resulted in the engine's degraded performance. According to the operator, the compressor, turbine, and bleed valve assemblies were overhauled about 2 years before the accident and then reassembled on the engine. The engine had operated about 766 hours since overhaul at the time of the accident. The engine manufacturer reported that the bleed valve assembly should be overhauled every 1,500 hours. No component log cards or historical information for the bleed valve was located during the investigation. According to the engine manufacturer, the bleed valve exhibited wear that was not consistent with a bleed valve with comparable service time. Therefore, it is likely that the bleed valve was likely not overhauled 2 years before the accident as reported by the operator and that it was beyond the overhaul period of 1,500 hours, which resulted in the observed wear that ultimately prevented the engine from producing sufficient power during takeoff.

Quoted verbatim from the NTSB record.