Previous accident report
NTSB Identification: WPR16LA150
14 CFR Part 91: General Aviation
Accident occurred Saturday, July 23, 2016 in Byron, CA
Probable Cause Approval Date: 03/05/2018
Aircraft: BEECH 65 A90, registration: N256TA
Injuries: 15 Uninjured.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
- The pilot’s failure to maintain an adequate airspeed and his exceedance of the airplane’s critical angle of attack, which resulted in an aerodynamic stall and subsequent spin. Also causal to the accident was the pilot’s failure to follow prescribed spin recovery procedures, which resulted in increased airspeed and airflow and the subsequent overstress separation of the right horizontal stabilizer. Contributing to the accident was the pilot’s inadequate preflight weight and balance calculations, which resulted in the center of gravity being aft of the limit.
On July 23, 2016, about 1900 Pacific daylight time, a Beech 65-A90, N256TA, sustained substantial damage following a loss of control while climbing out near the Byron Airport (C83) Byron, California. The commercial pilot and the 14 passengers were not injured. The airplane was registered to N80896 LLC, and operated by Bay Area Skydiving under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed for the sky-diving flight. The local flight departed C83 about 1851.
According to the pilot, as the airplane neared the planned jump area and altitude, about 12,500 ft, mean sea level, he initiated a left turn to line up for the drop zone. He stated the airplane's airspeed was a little slow and then "suddenly the airplane abruptly stalled, rolled off to the left, and began rotating nose-down." He stated that the airplane "did a couple of downward barrel rolls." One of the jumpers, seated in the co-pilots seat, heard a "loud bang" during the recovery sequence and stated that "the pilot did not retard the throttles during the recovery, causing the airplane to develop too much speed." The jumper further stated that during the recovery he felt the g-force on his stomach. The pilot said that he temporarily recovered the airplane to a wings level attitude for a few seconds and observed that the airplane was about 90° off the planned heading, and slow in airspeed.
Subsequently, the pilot stated there was a "shock" to the controls and "simultaneous the airplane suddenly broke hard to the left," stalled a second time, and began to rotate downward. The pilot told the sky-divers to jump out of the airplane. The parachutists complied, and all of them successfully exited the airplane during this second spin event. The pilot then initiated the spin recovery procedures to no apparent effect through about 9 rotations, and stated that the roll rate was a lot more rapid than the first spin event. He then pulled both propeller controls levers to the feather position and was able to get out the spin. He recovered the airplane to a wings and pitch level attitude, but shortly thereafter, the airplane "broke left" and stalled for a third time. The pilot recovered the airplane again by lowering the pitch attitude and increasing the airspeed.
The pilot turned back towards the airport and since the airplane was handling abnormally, he adjusted the elevator trim to its full nose up position to help him maintain straight and level flight. He stated that the full nose up trim setting was used on the approach. In addition, the pilot flew the approach 15 knots faster than required, in order to compensate for the control issue of a marked decrease in elevator performance.
The pilot described the landing as being nose low relative to a normal landing. After landing at C83, a witness observed that the airplane's right horizontal stabilizer, with the attached elevator, was missing. The separated airplane parts were subsequently located in a field a few miles south of the airport.
The pilot reported that there were no abnormalities with the airplane on the previous flights that day, or during his pre-flight inspection for the accident flight. He stated that the weather was clear and that there was a light chop. Further, he reported no engine issues during the flight.
Postaccident examination of the airplane revealed that the wing's top and bottom skins were unremarkable. The engine mounts, and the left horizontal stabilizer attachment points were examined for overstress, but none was observed. No signs of flutter were observed on the left horizontal stabilizer.
The right horizontal stabilizer, with the elevator attached, that had separated from the airplane, was examined. The right elevator and elevator trim tab remained attached to their respective attachment points. Fractures were observed on the main and trailing edge horizontal spars on the right horizontal stabilizer. There was some wrinkling on the skin surface. The attachment bracket that connected the right horizontal stabilizer to the airplane, and to the other horizontal stabilizer, exhibited fracture surfaces on the right side where the right horizontal stabilizer attached.
Portions of the right horizontal stabilizer, elevator, and the attachment bracket were sent to the National Transportation Safety Board Materials Laboratory for further examination. Magnified optical examination of the fractures surfaces revealed features consistent with overstress separations. No indication of fatigue or corrosion was observed. Deformation and fracture patterns in the right horizontal stabilizer spars were indicative of the stabilizer tip bending up and the lower spar also had upward tearing of the webs.
The airplane's flight manual spin recovery states: "immediately move the control column full forward, apply full rudder opposite to the direction of the spin, and reduce power on both engines to idle. These three actions should be done as near simultaneously as possible, then continue to hold this control position until rotation stops and then neutralize all controls and execute a smooth pullout. Ailerons should be neutral during recovery."
The airplane's weight and balance was calculated for the accident flight. The center of gravity (CG) was estimated to be about 6-7 units aft of the limit. Due the center of gravity (cg) being aft of the limit, the maximum allowable gross weight was unable to be determined at the time of the accident. According to the FAA Pilot Handbook of Aeronautical Knowledge states, "as the CG moves aft, a less stable condition occurs, which decreases the ability of the aircraft to right itself after maneuvering or turbulence."