Unintended Consequences

Unhappily, the accident record bears out this articles main point: Combining STCs and performing untested modifications can have lethal effects.

Editorial Staff

Tuesday, November 25, 2014 at 12:00 AM ET

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Key Takeaways:

Combining STCs and performing untested modifications can dangerously alter an aircraft's flight characteristics, as demonstrated by two fatal accidents.
One accident involved a Beechcraft Baron where combined STCs increased the VMCA, but the airspeed indicator was not updated, leading to a spin during a low-speed maneuver.
Another accident with a KR-2 experimental aircraft was linked to an unrecommended engine modification, which resulted in unknown spin characteristics and an uncontrolled descent after an intentional spin.

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Unhappily, the accident record bears out this articles main point: Combining STCs and performing untested modifications can have lethal effects.

August 7, 2010, Saltsburg, Pa., Beechcraft Model 58 Baron
The accident aircraft was modified by one STC that installed vortex generators (VGs) and by another for more powerful engines, different propellers, winglets and modified engine cowlings, which also increased the airplanes VMCA. However, the airplanes airspeed indicator remained marked to indicate a lower VMCA.