MIA99LA242

The pilot been doing aerobatic snap rolls. After approximately 10-15 snaps he began another. As he pulled on the stick he '...felt the ailerons brake loose.' He recovered from the snap at 2,500 feet agl. The airplane started a 20 degree to 30 degree steep descending turn to the right. He attempted to right the airplane with back stick and left rudder to no avail. He elected to make a controlled landing in a turn. About 600 feet agl the right wing went down to 90 degrees the nose then went down the same till impact with the ground. At no time did he have any directional or aileron control of the airplane. Laboratory examination of the inboard sections of the right aileron, the inboard aerodynamic compensator (spade) from the right aileron, and the outboard aerodynamic compensator from the left aileron, revealed, the in-flight loss of control was due to fatigue cracking and the subsequent fracture of the actuator lever attaching the right aileron to the control rod. In addition, the left aileron was cracked and a portion of this spar had been missing for some time. The fatigue cracking in the actuator lever from the right aileron and the rupture of the aft spar in the left aileron were precipitated by the fatigue cracking in the attachment structure of the inboard spade from the right aileron and the outboard spade from the left aileron.

On September 1, 1999, about 0930 eastern daylight time, a Sukhoi SU-29, N52PB, registered to Aerial Three Inc., impacted with the ground near unincorporated Fort Lauderdale, Florida. Visual meteorological conditions prevailed at the time, and no flight plan was filed for the 14 CFR Part 91 local personal flight. The airplane was destroyed. The commercial-rated pilot reported serious injuries. The flight had departed from the North Perry Airport, Hollywood, Florida, about 0900.

According to a witness, that was riding a lawn mower near the crash site, he saw the airplane at a low altitude, about 150-200 feet above the ground, heading in an easterly direction. The airplane turned 360 degrees to the right, descended, leveled off, for short time, then entered a steep nose low turn to the right, until it impacted the ground. In addition, the witness said the airplane was moving slow, after it had leveled off, and before it went into the nose low steep turn. The witness could not hear the sound of the airplane's engine because his lawn mower was running, and the noise of the lawn mower was too loud to hear anything.

The pilot stated, "...began doing aerobatic snap rolls. After approximately 10-15 snaps I began another. As I pulled on the stick I felt the ailerons brake loose. I recovered from the snap at 2,500 [feet] agl. The airplane started a 20 degree to 30 degree steep descending turn to the right. I tried to right the airplane with back stick and left rudder to no avail. At about 1,500 [feet] agl I decided I would make a controlled landing in a turn. At about 600 [feet] agl the right wing went down to 90 degrees the nose then went down the same till impact with the ground. At no time did I have any directional or aileron control of the airplane."

Examination of the wreckage revealed that the inboard aerodynamic compensator from the right aileron had failed. Examination of the airplane's records revealed that at the time of the accident that the ailerons were manufactured June of 1992, total time accumulated on the airframe was 331.6 hours, and 23 hours since the last airframe inspection.

The following components were removed from the airplane and examined at the NTSB Materials Laboratory, Washington, D.C. on October 20 to 22, 1999. The componets that were examined were; the inboard sections of the right aileron, and the inboard aerodynamic compensator (spade) from the right aileron, the outboard aerodynamic compensator from the left aileron.

The NTSB Materials Laboratory examination of the parts revealed fatigue cracking and a subsequent fracture of the actuator lever attaching the right aileron to the control rod. The examination further revealed that the aft spar in the left aileron was cracked and a portion of this spar had been missing for some time. The fatigue cracking in the actuator lever from the right aileron and the rupture of the aft spar in the left aileron were precipitated by the fatigue cracking in the attachment structure of the inboard spade from the right aileron and the outboard spade from the left aileron.

The examination revealed that all of the aileron's spades contained shims (washers) between the spacer and the attachment plate for the forward holes. The presence of the shims at the forward end of the spade attachment increased the aileron rational moment and, therefore, induced additional stresses to the spade attachment structures. According to the airplane's manufacturer a reinforcement kit had been manufactured for the spade attachment area. This kit had not been applied to the accident airplane. According to the manufactures records the reinforcement kit for the spades attachments were made available to the USA distributor of SU-29 airplanes before the accident, and before the owner of the airplane at the time of the accident had purchased the airplane from the previous owner. The previous owner of the airplane was also the USA distributor for the SU-29, when the reinforcement kits were made available. The airplane's records did show any entry indicating that the kits were installed.

According to the airplane's manufacturer the damage and fractures observed in the ailerons from the accident airplane were typically found in the ailerons that had exceeded the service life. It was revealed that the total time on the ailerons was not computed by the pilot in accordance to the formula that had been recommended by the manufacturer. The formula takes into account that the ailerons are subject to additional stress because the airplane is aerobic certified. In this case because the incorrect method of calculating total time, the reported total time on the ailerons (331.6 hours) was well below the total time calculated using the manufacturer's recommended formula. (See the NTSB Materials Laboratory Factual Report, an attachment to this report.)