A pitts S-2 became uncontrollable for unknown reasons and departed the runway after a normal landing...

Attributes
ACN	839289
Time
Date	200906
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	S-2 All Series
Operating Under FAR Part	Part 91
Flight Phase	Landing
Flight Plan	None
Person 1
Function	Single Pilot
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Engineer Flight Crew Flight Instructor Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 112 Flight Crew Total 9400 Flight Crew Type 150
Events
Anomaly	Deviation - Procedural Published Material / Policy Ground Event / Encounter Loss Of Aircraft Control Ground Excursion Runway

Narrative:

During landing rollout my aircraft suddenly and abruptly swerved to the left and departed the runway. The approach speed was 95 mph and touchdown was made on the runway centerline several hundreds feet past the threshold. I was decelerating with all 3 wheels on the ground when the aircraft swerved to the left at approximately 40 mph. I don't know the reason for the sudden change in direction but I did find some heavy plastic material in the left wheel pan. The brakes have not been inspected yet. Nobody was injured and no property other than the aircraft was damaged during this incident.

Original NASA ASRS Text

Title: A Pitts S-2 became uncontrollable for unknown reasons and departed the runway after a normal landing.

Narrative: During landing rollout my aircraft suddenly and abruptly swerved to the left and departed the runway. The approach speed was 95 MPH and touchdown was made on the runway centerline several hundreds feet past the threshold. I was decelerating with all 3 wheels on the ground when the aircraft swerved to the left at approximately 40 MPH. I don't know the reason for the sudden change in direction but I did find some heavy plastic material in the left wheel pan. The brakes have not been inspected yet. Nobody was injured and no property other than the aircraft was damaged during this incident.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.