Introduction
On March 5, 2021, about 1010 Pacific standard time, an Aermacchi Impala MB-326M, registration N155TP, was destroyed when it was involved in an accident near Edwards, California. The flight instructor sustained serious injuries, and the pilot receiving instruction sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight by the National Test Pilot School (NTPS).
Accident Sequence
According to the operator, the purpose of the flight in the light military jet trainer was spin data collection. The flight instructor reported that several maneuvers, including an inverted left spin, were conducted before the accident inverted left spin maneuver. Upon entry into the spin, the airplane behaved normally through three revolutions. The instructor noticed a steepening spin attitude and an increasing spin rate and directed the pilot receiving instruction to recover by stating, “recover, recover.” The pilot replied, “I’m trying.” The instructor looked down at the flight controls; the flight control stick appeared to be in the aft position, and the right rudder pedal was depressed. The spin rate started to incapacitate him, and it became clear that the pilot could not recover.
The flight instructor assumed control and attempted a recovery input. However, the spin rate was increasing with a corresponding increase in negative G forces, which pushed him out of his seat. He was able to touch the right rudder with his toes but could not apply sufficient right rudder control input to recover. Unable to recover and reaching the ejection decision altitude, he directed ejection by saying, “eject, eject, eject.” The pilot departed the airplane after the second ‘eject’ call. The spin rate continued to increase along with the negative G forces. Verifying that the pilot was clear, the flight instructor pulled his ejection handle. As he was being partially thrown out of the seat by the negative G forces, the seat impacted into his buttocks when the rocket catapult fired, resulting in a significant spinal fracture. His subsequent descent and landing under the parachute occurred normally.
The pilot receiving instruction reported that before the accident maneuver, 12 uneventful flight maneuvers were performed. While preparing for the accident maneuver, they climbed to about 22,000 ft mean sea level (msl). Power was set to idle, and a pitch-up motion was initiated. As the airplane entered the stall, he applied full left rudder and moved the stick full forward and to the right. The airplane entered a left inverted spin. While looking forward, he maintained the control positions during three spin revolutions then applied right rudder and moved the stick to center and full aft to recover. After two more spin rotations, the airplane showed no sign of recovery, and he repositioned the stick to neutral. The flight instructor then took control and attempted recovery. He heard a call from the telemetry room of “15,000 ft.” He looked at the altimeter and called out “13,000 ft” and “12,000 ft.” The flight instructor then ordered ejection. At the second ‘eject’ call, he pulled the lower ejection handle. His descent and landing under parachute occurred normally. The airplane descended to ground impact, and a postimpact fire erupted.
Postaccident Findings
The pilot receiving instruction reviewed the events with the NTPS chief pilot. While seated in the same type of airplane, he realized that the clearance between his shins and the instrument panel was small. While seated normally, he could move the rudder pedals to full left and right deflection. However, when he placed a cushion between himself and the seat (simulating a negative G scenario), the distance between his shins and the instrument panel was reduced. This allowed his shins to contact the instrument panel, restricting rudder pedal movement. Contact between his feet and the rudder pedals was accomplished only with his toes. Motion of the rudder was tested in that configuration, and the rudder moved only a few centimeters in either direction. When the rudder was depressed to the left, he could not move it right beyond the neutral position. This test was performed with the same type of equipment but without a G-suit and ejection seat leg restraining straps. The pilot recalled having difficulties applying full rudder deflection during recovery of both inverted spins on the day of the accident. Due to his shins contacting the instrument panel, he could only use his toes to move the rudder pedals while recovering.
The pilot further reported that his left leg (tibia and left foot) was injured during the accident. His flight suit’s lower left leg was torn, and there was scuffing on his left boot. He stated he did not know how the injury was sustained but speculated he was too tall for the airplane and that his left leg impacted the instrument panel during the ejection sequence.
Postaccident examination by a Federal Aviation Administration inspector revealed that all flight control surfaces were present. The flight control system sustained extensive impact and thermal damage. The examination did not reveal evidence of any mechanical anomalies that would have precluded normal operation.
The airplane was equipped with a Quasonix multimode telemetry transmitter. Transmitted data recorded at the NTPS flight operations center and provided to the National Transportation Safety Board showed the spin entry at 1005:00. Rudder position peaked at nearly 100% right near entry. Heading change showed the airplane was established in a developed spin. Rudder deflection throughout the spin varied, showing movement in both directions but generally lesser values than in previous spins. At 1005:46, about 10,730 ft msl, the value for vertical stabilizer strain gauge force aligned with values for rudder deflection. Due to data dropouts, it was not possible to determine the flight condition after the likely ejection time.