Rockwell S 2R N4907X

Summary

On 25 May 2019 at about 19:30 local time, a Rockwell S 2R registered N4907X, operated by Bearcreek Flying Service LLC, was involved in an accident near Oakes, North Dakota, 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

25 May 2019 at 19:30

Classification

Accident

Location

Oakes, North Dakota, United States

Coordinates

46.0969, -97.9194

Aircraft

Rockwell S 2R

Registration

N4907X

Category

Airplane

Year built

1974

Engines

1

Operator

Bearcreek Flying Service LLC

Operating rule

Part 137: Agricultural

Purpose of flight

Aerial Application

Phase of flight

Not recorded

Route

Oakes → Oakes

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CEN19LA156

Nobody was injured.

The failure of the helical cam gear of the engine assembly due to fatigue cracks in the gear teeth, which resulted in a total 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 was conducting an agricultural application flight in the turbopropeller-equipped airplane when the engine lost total power. The pilot maneuvered the airplane for a forced landing to an uneven field, resulting in substantial damage to the fuselage and wings. Teardown examination of the engine revealed that the teeth of the engine’s helical cam gear were fractured. Several of the gear teeth cracks showed signatures consistent with fatigue failure. The engine assembly had a relatively low time in service (485 hours) since its most recent overhaul. The helical cam gear assembly did not show pre-existing installation anomalies. The type and degree of damage to the helical cam gear was indicative of an uncoupling of the high-speed pinion from the helical cam gear of the engine torque sensor. The uncoupling event resulted in the continuous activation of the negative torque system, which likely drained the oil in the propeller and increased the propeller blade angle. This action would have resulted in an increase in engine operating temperature and subsequent loss of engine power.

Quoted verbatim from the NTSB record.