Amateur-built RV4 N173CW accident near Safford, Arizona

Probable cause

A loss of pitch control during the landing approach due to a jammed elevator control system.

NTSB analysis

The pilot was performing a routine flight over mountainous desert terrain to a destination he had flown to multiple times before. Visual meteorological conditions prevailed, with light winds and no turbulence.

ADS-B flight track information indicated that the airplane entered a nominal descent profile toward the destination airport; however, about 1 mile from the end of the presumed landing runway, the airplane began a rapid descent into rising terrain. After colliding with the ground, the airplane continued uphill 300 ft until coming to rest about 1/2 mile short and 40 ft below the approach end of the runway. The considerable distance travelled uphill after striking terrain indicated a relatively flat impact attitude and engine power at impact.

The rapid descent rate suggests that the pilot may have encountered pitch control difficulties; however, examination of the airframe did not reveal any evidence of primary flight control anomalies or a bird strike. The pitch trim system in the rear of the airplane was intact and functional; however, impact damage sustained to the front of the airplane precluded a complete determination of the pitch trim system state.

The airplane’s flaps were found fully extended, but flight track information indicated that the airplane did not slow to its flap deployment speed at any point during the approach. Damage to the flap electrical system prevented an accurate assessment of its operational status; therefore, an unintended deployment of the flaps could not be ruled out. However, under a runaway flap condition, the actuator motor would have deployed the flaps slowly, and flight testing revealed that any pitch-down forces caused by the flap deployment both with and without full nose-down trim would have been easily overcome by the pilot with the application of aft control stick forces. Further, at full extension, the flaps tended to act as air brakes. It is possible that he deployed the flaps intentionally to slow the airplane while struggling with a pitch anomaly.

During the examination, a foreign object (position light socket) that had previously been removed from the airplane was found in the lower underfloor bay of the aft seat, in an area that would have been occupied by the rear control column assembly. Although the forward control stick was fitted with a boot, the aft stick was not, leaving an open area into the control stick assembly. It is possible that either the socket or another unidentified object dropped into the open area and interfered with the free movement of the control stick, resulting in a pitch control jam and a rapid descent.

Text from the NTSB. Open the NTSB docket for WPR20LA176 for the full record.