N52VYYakovlev YAK 52 · 1985

On February 08, 2010, about 1250 Pacific standard time, an experimental Yakovlev Yak 52, N52VY, collided with terrain while maneuvering near Redlands, California. The owner/pilot was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The commercial pilot and pilot-rated passenger were killed; the airplane was substantially damaged. The local area personal flight departed from Redlands about 1230. Visual meteorological conditions prevailed, and no flight plan had been filed.

Numerous witnesses to the accident were interviewed by a Safety Board investigator. One witness reported observing the airplane perform aerobatics and then return to the airport. The pilot shut down the airplane and deplaned. Shortly thereafter, he boarded the airplane and departed again, proceeding directly to the aerobatic box just northeast of the airport. The airplane completed several loops and other maneuvers over the course of about 10 minutes. The witness observed the airplane in a rapid descent in a nose low position with the wings rocking about the longitudinal axis.

Another witnesses stated that the pilot asked for a funnel to put oil in the onboard smoke system. A short while later, the airplane departed and the pilot performed aerobatics for about 10 to 15 minutes. He observed the airplane at a low altitude begin a spin with white smoke emanating from the smoke machine. The airplane's rotation increased as the airplane neared terrain and subsequently crashed.

Pilot

A review of Federal Aviation Administration (FAA) airman records revealed that the 27-year-old pilot held a commercial pilot certificate with single and multi-engine land airplane, and rotorcraft-helicopter ratings; he additionally had an instrument airplane rating. The pilot held a second-class medical certificate that was issued on October 30, 2006, with the limitation that he must wear corrective lenses while exercising the privileges of his airman certificate.

According to the pilot's personal flight logbook he had a total flight experience of 277.8 hours, with 188.7 accrued in single-engine airplanes and 67.3 in rotorcraft. He had amassed 21.1 hours in the Yak 52, which included 7.7 hours of dual aerobatic training and 5.2 hours of solo aerobatic time.

Pilot-rated Passenger

According to the FAA airman records, the 29-year-old passenger held a commercial pilot certificate with airplane ratings for multi-engine land and instrument airplane; she held a private pilot certificate with an airplane single-engine land rating. A third-class medical certificate was issued to her on March 08, 2007, with no limitations.

No personal flight records were recovered for the passenger. On the application for her last medical certificate, the passenger stated that her total flight experience was 200 hours.

The pilot and pilot-rated passenger were both California Air National Guard officers who flew unmanned aircraft systems (UAS). Specifically, both were pilots of the MQ-1 Predator. The pilot appeared to have been positioned in the front seat and the passenger in the back seat; both were secured to their shoulder harnesses.

The airplane was manufactured in 1985, and registered in the United States in July 2002. It is a single-engine, two seat (tandem configuration), low-wing primary trainer that is primarily metal construction and has full aerobatic capability. The engine, a Vedenev M-14P, is a nine-cylinder radial rated at 360 horsepower. It was equipped with a three-bladed wood/composite propeller.

No maintenance logbooks were found during the course of the investigation. Copies of maintenance activities were obtained from the maintenance facility that the pilot took the airplane to. At the last condition inspection, completed on February 24, 2009, the airframe's total time was noted as 963 hours; the engine total time was 1,402 hours. It is unknown how many hours had been accumulated since that inspection.

The wreckage was located at an elevation of about 1,660 feet mean sea level (msl), and was approximately 1.2 nautical miles from the Redlands airport on a bearing of 60 degrees. The wreckage was on relatively flat terrain consisting of rocks and low vegetation.

The main wreckage, consisting of the fuselage, tail section, and wings, had come to rest within the aerobatic box designated near the airport. There was a shallow crater in the dirt a few feet aft of the wreckage. The entire wreckage was all within the same area and the wings and fuselage came to rest upright in a relatively level attitude.

The nose had been pushed back into the fuselage giving the airframe skin an "accordioned" appearance. The bottom skin of the tail section had detached from the fuselage and only remained attached by the top skin. The tail section had "scorpioned" forward toward the fuselage and right wing, coming to rest with the bottom facing upward. The large portions of the propeller blades had splintered, most of which was in close proximity to the engine. The left wing came to rest with the mid section leading edge wrapped around a boulder, creating a shallow divot.

The San Bernardino County Coroner completed an autopsy on the pilot and passenger. Specimens of the pilot were retained for toxicological testing by the FAA Toxicology and Accident Research Laboratory in Oklahoma City. The results of analysis of the specimens were negative for carbon monoxide, volatiles, and tested drugs.

Following recovery, a Safety Board investigator examined the airplane at a salvage facility, Aircraft Recovery Services, in Pearblossom, California, on March 25, 2010. Present to the examination was several inspectors from the FAA Riverside Flight Standards District Office (FSDO).

The left wing remained affixed to the fuselage with the aileron and wing flap control surfaces still attached at their respective hinges. The wing sustained aft crush deformation to the inboard section, with the leading edge skin folded into itself; the damage was primarily on the bottom skin. The aileron control surface had sustained crush damage which was primarily present to the bottom.

The right wing remained affixed to the fuselage with the aileron and wing flap control surfaces still attached at their respective hinges. The leading edge displayed crush deformation with the skin folded into itself giving an accordioned appearance. The crush began inboard near the right main landing gear and increased gradually with the greatest crush deformation present in the most outboard portion of the wing. The wing tip was not attached.

The empennage was intact and all cables were attached to the control surfaces. The cable ends were severed by recovery personnel near the area where the tail skin had been detached. Rudder and elevator continuity were verified from the control surfaces to the entangled cockpit area, which had sustained too much crush damage to confirm continuity to the cockpit controls.

During the examination no evidence of mechanical malfunctions or failures were found.

Aerobatic Maneuvers

Within the wreckage two pieces of paper were found on the pilot's kneeboard labeled "International Aerobatic Club." According to an industry expert, this is referred to as a "known sequence" for an International Aerobatic Club contest at the sportsman level, which is essentially a beginners' skill level. The pilot had pages on his kneeboard showing how the maneuvers are to be performed based on the prevailing wind direction and the order they are to be performed.

The industry expert further stated that while the pilot had these papers on his kneeboard, it is not unusual for pilots to deviate from it to practice, sometimes practicing only a few choice maneuvers. The papers, as well as a full description of the maneuvers listed on them, are contained within the public docket for this accident.

Literature

According to the FAA's Flight Training Handbook, a spin is described as an aggravated stall that results in "autorotation," wherein an airplane follows a corkscrew path in a downward direction. When an airplane's angle of attack is excessive enough to produce a stall, the airplane's nose will pitch down. If any adverse yaw is present, one wing will usually drop, and an autorotation begins. Airplane spins are categorized as normal upright, normal inverted, flat upright, flat inverted, and may be classified as normal or accelerated. The FAA's standard spin recovery sequence for a normal, upright spin, is to 1) reduce engine power, 2) apply opposite rudder to slow the rotation, 3) apply positive forward elevator movement to reduce the angle of attack and break the stall, 4) neutralize the rudder as spinning stops, and, 5) return to level flight.

Video

A witness located near the accident site recorded a short video of the airplane on his cellular phone. The grainy video captured the several seconds prior to impact, displaying a smoke trail which was presumably left from the onboard smoke system. The poor quality of the video makes it not possible to definitively discern the control surface deflections, propeller rpm, or exact nature of the flight path.

Several Yak 52 experts were sourced and shown the video images of the smoke trail and airplane just prior to impact. One stated that the smoke trail indicates that airplane was in a spin, but could not determine as to whether it was fully developed, flattened, or with power; he could not discern if any recovery control inputs were initiated. He opined that the smoke trail showed that the airplane was in a spin of at least three turns and would therefore likely be fully developed. He noted that the smoke "corkscrew" tightens (smaller diameter) significantly after two visible turns indicating a lower nose attitude and therefore the airplane was most likely recovering from the spin.

He additionally stated that the height loss per rotation doesn't appear to alter too much when the aircraft is in the recovery stage, which would indicate the airplane was in a conventional spin rather than a flattened one (an airplane in a flattened spin presents a larger plan area to the airflow and thus descends less per rotation). He concluded that based on the video, the airplane appeared to be in a conventional spin which it recovered at too low of an altitude from which a safe flight path was possible resulting in an impact at slow speed with a high descent rate.

Human Factors

According to a Research Psychologist at the FAA Human Factors Laboratory, the Predator, because of the Stability Augmentation System (SAS) flight controls, is not able to perform aerobatic maneuvers and most flights would not involve severe maneuvers. He stated that flying aerobatics in a Yak would be very different from piloting the Predator and he opined that therefore, the Predator experience did not contribute negatively to the accident.

A flight surgeon with the United States Air Force stated that although he has not seen any research of the effects of unmanned to manned aircraft, but areas of concern for the change are as follows:

Negative transference: The buttons and operations of the basic controls (throttle and stick) for the UAS appear to be similar to manned aircraft but operate very differently depending on what autopilot hold modes are operational.

Physiologic de-conditioning: The extensive time spent at 1G with no exposure to acceleration forces could lead to forgetting or poor application of anti-G straining maneuvers and actually decrease resting G tolerance.

In a conversation with two UAS pilots, both who have experience flying Predators, they stated that flying manned aircraft versus unmanned was completely different. They further stated that negative transference, specifically in aerobatic maneuvers, would be non-existent, since the Predator is primarily flown in a level attitude at slow airspeeds.