ERA24FA088 · Beech 95-B55 (T42A)

The flight instructor, commercial-certificated/multi-engine-rated pilot receiving instruction, and a passenger departed on a local flight to practice maneuvers so the pilot could obtain currency in a multi-engine airplane. The pilot receiving instruction had not flown a twin-engine airplane in almost 11 years. This was his first time flying this make/model airplane, and with this flight instructor. Shortly after departure, the airplane climbed to about 3,000 to 3,300 ft mean sea level (msl) and made four alternating left and right 360° turns. After the fourth 360° turn, the airplane began to climb, reaching an altitude of about 4,000 ft msl. The airplane then entered a rapid descent and impacted terrain. Witnesses described that the airplane “corkscrewed” or “spiraled” as it descended nose-down toward the ground. Other witnesses said the airplane sounded as if it were having engine trouble. The airplane came to rest upright with evidence of little forward movement, consistent with the airplane being in a flat attitude at the time of impact. All major components of the airplane were accounted for at the site, and there was no postimpact fire. Photos taken by first responders revealed some airframe icing on the airplane’s left wing, left engine cowling, and nose baggage area. Weather at the time included wind gusts up to 23 kts, with an active AIRMET (Airman Meteorological Information) for icing and a SIGMET (Significant Meteorological Information) for severe turbulence between 3,000 and 16,000 ft msl. A postaccident examination of the airplane and engines revealed no preimpact mechanical deficiency that would have precluded normal operation. Based on the witness’ description of the airplane’s descent and the condition of the wreckage, the airplane entered a spin from which it was not recovered. Since an airplane must first be in a stalled condition before it can spin, either an inadvertent or deliberate stall must have immediately preceded the spin. Further, because a spin entry requires the presence or introduction of a yawing moment at the stall, the NTSB conducted an airplane performance study that considered possible conditions and scenarios that could affect the airplane’s stall performance and produce a yawing moment. These considerations included airframe ice contamination, operation of the engines at different thrust levels (such as during a Vmc demonstration, which is commonly performed during multi-engine airplane instructional flights to demonstrate the airplane’s minimum control airspeed with one engine deliberately shut down or set to minimum thrust), and improper stall recovery technique. The study determined that the airplane entered two stalls in the minute before the accident. The airplane was successfully recovered from the first stall but not the second, during which the spin developed and continued to ground impact. The study determined that, during each stall, the airplane achieved the nominal flaps-up stall speed outlined in the airplane flight manual (AFM). As such, there was no evidence that airframe icing contamination adversely affected the airplane’s stall speed or other aerodynamic characteristics, such as asymmetric stall behavior (one wing stalling before the other). In addition, the study determined that the computed engine power required during the time surrounding the first stall exceeded the power available from one engine, indicating that both engines must have been operating at the time of the first stall. This was inconsistent with a scenario involving a Vmc demonstration. The study determined that, at the time of the second stall, the required engine power was reduced compared to the first stall. Given that this second stall occurred less than 30 seconds after the first, the performance study concluded that it was unlikely that the second stall was associated with an attempted Vmc demonstration. Having excluded an asymmetrical aerodynamic condition and asymmetrical engine thrust as potential sources of the yawing moment that induced the airplane’s spin, the study concluded that the spin may have resulted from an improper stall recovery technique, possibly involving an excessive or inadvertent rudder input. FAA guidance for pilots related to spin avoidance in multi-engine airplanes emphasizes initiating stall recovery (reducing the airplane’s angle of attack) as soon as the airplane reaches the stall warning, such as an aural alert or buffet. The guidance references stall practice among the scenarios in which “spin awareness must be at its greatest.” Toxicological testing of the flight instructor identified that he had used multiple central nervous system (CNS) depressants, including medications for anxiety and depression. Although postmortem drug levels do not reliably predict specific impairing effects in this case, the presence of multiple CNS depressants increased the risk of adverse CNS effects, such as increased sedation, decreased alertness, slowed reflexes, and impaired concentration; these effects can potentially occur despite chronic use. The status of the flight instructor’s underlying condition and its response to treatment could not be determined. As pilot-in-command, the flight instructor had ultimate responsibility for the safety of the flight. It is possible that the flight instructor’s judgment may have been adversely affected by his substance use or underlying condition, or both. Also, despite the predictable need to be immediately ready to react to prevent a spin, the experienced flight instructor failed to prevent the spin. The adverse effects of his substance use, the associated underlying condition, or both likely diminished his capacity to act in a timely and appropriate manner, although a more specific determination of the individual contributions of specific medical factors is not possible based on the available evidence.

Verbatim NTSB analysis and probable cause from the NTSB dataset