Lack of performance data a factor in crash

This August 2010 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

Aircraft: Beech Baron. Injuries: 2 Fatal. Location: Saltsburg, Pa. Aircraft damage: Destroyed.

What reportedly happened: The 65-year-old pilot, who had a commercial ticket and more than 1,500 hours multi-engine time, bought the airplane four days before the accident. Two days before the accident he performed three full-stop landings to get current. The pilot’s insurance company broker suggested that he obtain a multiengine instrument proficiency check-ride. He attempted to do the checkride with an FAA designated pilot examiner acting as CFI. The airplane was equipped with a throw-over yoke. However, the DE did not have an exemption from 14 Code of Federal Regulations 91.109(a) to give instruction in an aircraft equipped with a throw-over control yoke.

The airplane had undergone several modifications that required a supplemental type certificate, including the addition of vortex generators (VGs), which decreased the airplane’s air minimum control airspeed (Vmca) from 81 knots to 74 knots. The VG STC took into account a change to only the original type design and increased the airplane’s Vmca to 87 knots, however, the airplane’s airspeed indicator remained marked to indicate a Vmca of 74 knots. Another STC installed more powerful engines, different propellers, winglets, and modified engine nose cowlings.

A representative of the current holder of the STC reported that, to his knowledge, no flight testing was performed on the accident airplane or any similar make and model airplane to determine the interrelationship between his company’s STC and the previous STC. Therefore, the actual performance data for the accident airplane, including the Vmca, were unknown. However, because of the installation of more powerful engines, the Vmca was likely higher than the 74-knot Vmca marked on the airspeed indicator.

According to radar data, the airplane took off and headed to the northwest. It climbed to 3,600 feet and performed two 360° nearly level turns to the left, followed by a 360° turn to the right. The airplane then climbed to 4,200. The ground speed decreased to 127 knots, then it descended to 3,900 feet. The airplane stayed at that altitude, making several heading changes. The ground speed decreased to about 71 knots. Witnesses on the ground stated that the airplane was in level flight before it descended in a left spin. Several witnesses reported a sputtering noise coming from the airplane. The airplane crashed into a home and caught fire.

The only major components of the airplane that were not extensively damaged by fire were the outer section of the left wing and one cargo door, both of which were found in close proximity to the house. Both engines and their accessories and both propellers were extensively damaged. Although the right engine-driven fuel pump drive coupling was found fractured, this likely occurred during post-accident rotation of the crankshaft to facilitate removal of the propeller. The extensive damage limited the airframe and engine testing that could be performed, however, there was no evidence of pre-impact failure or malfunction on the observed components.

Based on the airplane’s decreasing airspeed and nearly level altitude, the pilot was likely performing either imminent stall or simulated loss of engine power air-work before the plane aerodynamically stalled and then entered a spin. Because the airplane was equipped with only a throw-over control yoke, the CFI had limited ability to assist in the recovery of the airplane. Although it was not possible to determine which low-airspeed maneuver was being demonstrated, one scenario that is consistent with the radar data evidence is the Vmca demonstration, which requires a power reduction on one engine (and is consistent with the witnesses’ descriptions of “sputtering” engine sounds). If the pilot were performing a Vmca demonstration, it is possible that the airplane began to lose directional control earlier than expected because the actual Vmca of the airplane with multiple STC modifications was unknown, and the airspeed indicator was improperly marked.

Although the limitations and conditions section of STC SA1762SO stated that the installer must determine that the relationship between that STC modification and any other previously approved modifications “will not produce an adverse effect upon the airworthiness of that airplane,” the investigation found that the FAA does not provide any guidance to an installer to help determine the interrelationship between multiple STCs. As a result of this accident, on Dec. 29, 2011, the FAA issued Airworthiness Directive (AD) 2011-27-04 that requires an inspection for airplanes equipped with STC SA1762SO and that specifies corrective action, if applicable, to ensure that the airplanes have the correct Vmca marking on the airspeed indicator, taking into consideration other STC modifications.

Probable cause: The pilot’s loss of control of the airplane during low-airspeed air-work and his failure to promptly recover the airplane from the aerodynamic stall, which resulted in a spin. Contributing to the accident were the pilot and CFI’s intentional operation of the airplane for the purpose of performing instructional air-work with only a throw-over control yoke installed. The pilot’s lack of recent flight experience in the airplane make and model and the lack of accurate performance data for the modified airplane was a factor.

For more information: NTSB.gov. NTSB Identification: ERA10FA404