Pilot Debrief

PITTS S1E near Seguin, TX — 2024-11-17

Final reportCEN25LA043
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Date
2024-11-17
Location
Seguin, TX, USA
Airport
1TE4
Aircraft
PITTS S1E
Registration
N52B
Category
Airplane
Highest injury
None
Fatalities
0

Probable cause

The improper construction of the rudder cable assembly by the airplane builder, which resulted in the fatigue failure of the left rudder cable during the landing roll and the pilot’s subsequent inability to maintain directional control.

NTSB narrative

The pilot was practicing aerobatic maneuvers in the experimental biplane. After performing several maneuvers, he initiated a snap roll by applying full throttle, full aft elevator, and full left rudder. The pilot stated that immediately after rudder application, he felt the rudder pedal “lose tension and go to the firewall.” The airplane stopped the snap roll in an inverted spiral descent. The pilot recovered with aileron and elevator, and found that while he still had right rudder control, he was unable to center the rudder due to the unresponsive left rudder pedal. The pilot returned to airport for landing and found that he was able to apply left rudder by pulling on the left rudder cable with his hand. The pilot subsequently landed the airplane, and during the landing roll, the airplane veered to the right. Pulling on the left rudder cable did not provide adequate rudder control authority, and the airplane ground-looped, nosed over, and came to rest inverted, resulting in substantial damage to the vertical stabilizer, lower left wing, and upper wings. Postaccident examination revealed that the left rudder cable had separated at the attachment linkage to the left rudder pedal. Additionally, the right rudder cable thimble at the linkage attachment point was separated and missing a section the same thickness as the linkage. The rudder cables were likely installed with similar configurations, using a thimble to line the inside of the attachment loop and a ferrule to secure the loop in place. The thimble lining on the inside of the right cable loop had failed, with a section of the thimble missing from the apex of the loop. This missing section was large enough for the linkage to fit in the gap, indicating that the linkage was pulling directly on the cable when the cable was in tension. Examination of the rudder cables revealed signatures consistent with severe wear and fatigue. This was exacerbated by contact with the 90° corners of the linkage attachment through hole. The airplane build plans stated that the rudder cable linkage attachment through hole must be chamfered to 45° on both sides on the outside corners. Examination of the linkage attachments revealed that neither the right nor left rudder cable linkage attachment holes had been chamfered in accordance with the build plans. The linkage for both cables and the right cable thimble displayed rubbing damage due to contact with the unchamfered hole. The left cable, before its failure, was likely in a similar condition to the right, and the thimble also likely failed on the left cable. This resulted in fatigue cracking of the cable strands due to repeated rubbing and loading on the unchamfered through hole and the subsequent failure of the left rudder cable. Review of the airframe maintenance logbook revealed no entries for rudder cable replacement. It is likely that the cables were original to the airplane and had been in service for 38 years and 1,751 hours of operation at the time of the accident. The mechanic who conducted the airplane’s most recent annual condition inspection stated that he did not typically inspect the inside radius of a cable’s attachment loops during his flight control inspection, as long as the cable was otherwise in good condition.

NTSB coding

Evidence available

  • Photos
  • 6 docket documents
View NTSB final reportView NTSB docket

Docket documents6

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