NUMEROUS WITNESSES REPORTED THAT SHORTLY AFTER COMPLETING ITS TURN ONTO THE
FINAL APPROACH COURSE TO RUNWAY 35 AT COLORADO SPRINGS MUNICIPAL AIRPORT, THE
AIRPLANE ROLLED STEADILY TO THE RIGHT AND PITCHED NOSE DOWN UNTIL IT REACHED A
NEARLY VERTICAL ATTITUDE BEFORE HITTING THE GROUND. NONE OF THE ANOMALIES FOUND
WITH THE HYDRAULIC AND FLIGHT CONTROL SYSTEMS WOULD EXPLAIN AN UNCOMMANDED
ROLLING MOTION OR INITIAL LOSS OF CONTROL OF THE AIRPLANE. GALLING FOUND ON THE
INPUT SHAFT AND BEARING FROM THE STANDBY RUDDER ACTUATOR POWER CONTROL UNIT
COULD NOT CAUSE SUFFICIENT RUDDER DEFLECTION TO RENDER THE AIRPLANE
UNCONTROLLABLE. THE AIRPLANE ENCOUNTERED A NUMBER OF OROGRAPHICALLY INDUCED
ATMOSPHERIC PHENOMENA INCLUDING UPDRAFTS AND DOWNDRAFTS, GUSTS, AND VERTICAL AND
HORIZONTAL AXIS VORTICES. HOWEVER, THE FDR DOES NOT CONCLUSIVELY SUPPORT AN
ENCOUNTER OF A VORTEX OF THE STRENGTH NECESSARY TO CAUSE AN UNCONTROLLABLE ROLL
OF THE AIRPLANE.
Probable Cause
LOSS OF CONTROL FOR UNDETERMINED REASONS. THE TWO MOST LIKELY EVENTS THAT COULD
HAVE RESULTED IN A SUDDEN UNCONTROLLABLE LATERAL UPSET ARE A MALFUNCTION OF THE
AIRPLANE'S LATERAL OR DIRECTIONAL CONTROL SYSTEM OR AN ENCOUNTER WITH AN
UNUSUALLY SEVERE ATMOSPHERIC DISTURBANCE. ALTHOUGH ANOMALIES WERE IDENTIFIED IN
THE AIRPLANE'S RUDDER CONTROL SYSYTEM, NONE WOULD HAVE PRODUCED A RUDDER
MOVEMENT THAT COULD NOT HAVE BEEN EASILY COUNTERED BY THE AIRPLANE'S LATERAL
CONTROLS. THE MOST LIKELY ATMOSPHERIC DISTURBANCE TO PRODUCE A RUDDER MOVEMENT
WAS A ROTOR (A HORIZONTAL AXIS VORTEX) PRODUCED BY A COMBINATION OF HIGH WINDS
ALOFT AND THE MOUNTAINOUS TERRAIN. CONDITIONS WERE CONDUCIVE TO THE FORMATION OF
A ROTOR, AND SOME WITNESS OBSERVATIONS SUPPORT THE EXISTENCE OF A ROTOR AT OR
NEAR THE TIME AND PLACE OF THE ACCIDENT. HOWEVER, TOO LITTLE IS KNOWN ABOUT THE
CHARACTERISTICS OF SUCH ROTORS TO CONCLUDE DECISIVELY WHETHER THEY WERE A FACTOR
IN THIS ACCIDENT. (NTSB REPORT AAR-92/06)