Accident Description
During a landing, a pilot receiving instruction in a high-performance tailwheel-equipped airplane reported that the initial touchdown resulted in porpoising. Subsequently, the airplane settled onto the ground in a three-point landing attitude. During the landing roll, the airplane veered to the left. The pilot applied moderate right rudder to compensate, then applied heavy right rudder, but was unable to arrest the veer. The airplane ground looped to the left, causing the right main landing gear to collapse and the right wing to impact the ground. The airplane sustained substantial damage to the right wing.
The pilot reported no preaccident mechanical malfunctions or failures that would have precluded normal operation.
Porpoising in Landings
The Federal Aviation Administration's Airplane Flying Handbook (FAA-H-8083-3A, 2004) discusses porpoising. It states that a bounced landing that is improperly recovered can cause the airplane to come in nose first, setting off a series of motions resembling the jumps and dives of a porpoise. The problem is an improper airplane attitude at touchdown, sometimes caused by inattention, not knowing where the ground is, mistrimming, or forcing the airplane onto the runway.
Ground effect decreases elevator control effectiveness and increases the effort required to raise the nose. Not enough elevator or stabilator trim can result in a nose-low contact with the runway, leading to porpoising. Additionally, improper airspeed control can cause porpoising; an approach that is too fast may result in floating, and attempting to force the airplane onto the runway when it still wants to fly can lead to porpoising. The handbook also notes that porpoising can be triggered by a gust of wind, a bump in the runway, or even a slight tug on the control wheel.
The corrective action for a porpoise is similar to that for a bounce and depends on severity. When it is very slight and there is no extreme change in pitch attitude, a follow-up landing may be executed by applying sufficient power to cushion the subsequent touchdown and smoothly adjusting the pitch to the proper touchdown attitude.