NTSB Identification: WPR10LA253
14 CFR Part 137: Agricultural
Accident occurred Friday, May 21, 2010 in Robbins, CA
Probable Cause Approval Date: 09/13/2012
Aircraft: SCHWEIZER AIRCRAFT CORP G-164B, registration: N3633C
Injuries: 1 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

During an agricultural application flight, the pilot noticed that the right brake pedal was stiff and saw what appeared to be hydraulic fluid on his foot. The pilot tried without success to set and release the brake to correct the stiff brake pedal. He radioed his base of operations to notify ground personnel of the possible brake problem and of his intention to return to the airfield. The pilot attempted to land the tailwheel-equipped airplane with a direct crosswind that was 15 knots, gusting to 20 knots. As soon as the airplane’s right wheel touched down, the pilot felt the airplane start to pull to the right. When he tried to correct the airplane’s direction to the left, the pilot felt the wind shift and the airplane veered off the left side of the runway into an adjacent irrigation ditch. The left wing came to rest on the sloping terrain forming the ditch. The investigation showed that the right brake calipers separated from the airplane at touchdown. Examination of the right wheel revealed that the inner wheel hub flange sustained a circumferential failure that allowed the inflated tire and tube to expand and impinge upon the brake disc and caliper. The examination further showed that the tire installed on the airplane was a larger size than the standard tire size recommended by the manufacturer of the wheel assembly (29x11.0-10 instead of 8.50-10). Because of its larger-than-standard size, the tire impinged on the brake disc and caliper after the wheel hub flange failed, which resulted in the caliper’s separation upon touchdown.

According to the type certificate holder for the airplane, some G-164B operators of the accident airplane model have obtained field approval from their local Federal Aviation Administration (FAA) flight standards district office to use the oversize tires. The FAA had issued such a field approval for the accident airplane. As a result of this accident and the subsequent investigation, on December 15, 2010, the FAA issued Special Airworthiness Information Bulletin CE-11-06, which reminded operators that oversized tire modifications require analysis and substantiation as well as periodic inspections to prevent unsafe conditions, none of which were accomplished in this case.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The failure of the wheel hub flange, which allowed the over size tire to expand and impinge on the brake disc and caliper, which resulted in a loss of control during the landing.

Full narrative available

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