Tuesday, June 14, 2016

American Champion 8KCAB Decathlon, N244SF: Accident occurred June 04, 2016 in Black Diamond, King County, Washington


NTSB Identification: GAA16CA281
14 CFR Part 91: General Aviation
Accident occurred Saturday, June 04, 2016 in Black Diamond, WA
Probable Cause Approval Date: 08/31/2016
Aircraft: AMERICAN CHAMPION AIRCRAFT 8KCAB, registration: N244SF
Injuries: 1 Minor.

NTSB investigators used data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator and did not travel in support of this investigation to prepare this aircraft accident report.

The pilot of the tailwheel equipped airplane reported that during touchdown the airplane porpoised and drifted off the runway to the right. The pilot further reported that he initiated an aborted landing procedure, but the airplane aerodynamically stalled, impacted the ground, and nosed over. 

The airplane sustained substantial damage to the empennage.

According to the pilot there were no preimpact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation. 

The Federal Aviation Administration has published the Airplane Flying Handbook FAA-H-8083-3A (2004). This handbook discusses aerodynamic stalls and states in part:

The key to stall awareness is the pilot's ability to visualize the wing's angle of attack in any particular circumstance, and thereby be able to estimate his/her margin of safety above stall. This is a learned skill that must be acquired early in flight training and carried through the pilot's entire flying career. The pilot must understand and appreciate factors such as airspeed, pitch attitude, load factor, relative wind, power setting, and aircraft configuration in order to develop a reasonably accurate mental picture of the wing's angle of attack at any particular time. It is essential to flight safety that a pilot takes into consideration this visualization of the wing's angle of attack prior to entering any flight maneuver.

Stall accidents usually result from an inadvertent stall at a low altitude in which a recovery was not accomplished prior to contact with the surface.

The Federal Aviation Administration has published the Airplane Flying Handbook FAA-H-8083-3A (2004). This handbook discusses porpoising and states in part:

In a bounced landing that is improperly recovered, the airplane comes in nose first setting off a series of motions that imitate the jumps and dives of a porpoise—hence the name. The problem is 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 and a porpoise develops.

Porpoising can also be caused by improper airspeed control. Usually, if an approach is too fast, the airplane floats and the pilot tries to force it on the runway when the airplane still wants to fly. A gust of wind, a bump in the runway, or even a slight tug on the control wheel will send the air plane aloft again. 

The corrective action for a porpoise is the same as for a bounce and similarly depends on its severity. When it is very slight and there is no extreme change in the airplane's 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.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot's abnormal runway contact during the landing flare, which resulted in a porpoise, aerodynamic stall, impact with terrain, and nose over.

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