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

Verified

Key Takeaways:

Untested aircraft modifications, including combining multiple Supplemental Type Certificates (STCs) or significant design deviations, can introduce unforeseen and lethal flight characteristics.
One accident involved a Beechcraft Baron with combined STCs that increased its minimum control airspeed (VMCA), but an unupdated airspeed indicator contributed to a fatal spin during maneuvers.
Another incident featured an experimental aircraft with an unrecommended heavier engine and untested modifications that entered an unrecoverable spin, highlighting the dangers of flying with unknown aircraft characteristics.

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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.