Accident Rockwell S-2R Thrush Commander N8520V, 23 Jun 2011
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ASN Wikibase Occurrence # 136810
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Type:Silhouette image of generic SS2P model; specific model in this crash may look slightly different    
Rockwell S-2R Thrush Commander
Owner/operator:Farm Aviation Inc
Registration: N8520V
MSN: 2280R
Fatalities:Fatalities: 0 / Occupants: 1
Aircraft damage: Substantial
Location:Near Brawley, CA -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Departure airport:Brawley, CA (BWC)
Destination airport:Brawley, CA (BWC)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
The pilot was en route to perform an aerial application pass when the airplane’s engine lost partial power. He made a forced landing in a nearby pasture; however, the airplane struck a railroad track during the landing roll, and a postcrash fire ensued. Examination of the radial engine revealed that the connecting rods for the pistons in cylinders 3 and 8 had failed, resulting in significant internal engine damage and the partial loss of power. Examination of the remains of the connecting rods for both cylinders revealed wear signatures that were mostly consistent with engine operation after failure. Because the engine continued operating after the failure, most features on the connecting rods fracture surfaces were obliterated, which made it difficult to identify the initial failure. However, further examination of the inside diameter surfaces of the wrist pin bearing of the number 3 cylinder connecting rod revealed wear signatures consistent with normal engine operation. Based on this finding, it is most likely that the event was initiated by the failure of the number 3 piston rod because it was not affected by the continued operation of the engine.

The design of the engine's fuel priming system was such that cylinder number 3 was prone to piston hydraulic lock due to its low position within the priming system. Hydraulic lock is caused by excessive fuel being injected into a cylinder prior to engine start, and can be caused by either excessive priming, or a failure in the plunger or check valve assemblies, either of which could result in fuel trickling from the lowest nozzle within the system during non-operation. Postaccident fire damage precluded a thorough examination of the plunger and check valve assemblies. Hydraulic lock can result in a bent connecting rod and subsequent rod failure. The airplane was a low wing type, with integral wing fuel tanks located below the engine, and as such, it is unlikely that fuel had leaked into cylinder number 3 during non-operation.
Probable Cause: The partial loss of engine power shortly after takeoff, which likely resulted from the failure of the piston connecting rod in cylinder number 3 due to hydraulic lock in that cylinder.



Accident investigation:
Investigating agency: NTSB
Status: Investigation completed
Duration: 1 year 1 month
Download report: Final report
Other occurrences involving this aircraft

11 Mar 2004 N8520V Farm Aviation Inc. 0 near Calipatria, California sub


Revision history:

24-Jun-2011 06:23 gerard57 Added
24-Jun-2011 08:28 RobertMB Updated [Time, Aircraft type, Registration, Cn, Operator, Location]
21-Dec-2016 19:26 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
27-Nov-2017 16:58 ASN Update Bot Updated [Operator, Other fatalities, Departure airport, Destination airport, Source, Narrative]

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