Hardware failure leads to severe vibration and loss of control in King Air 90

Casualties unknown • Aircraft Services Directorate, CA

A training flight in Ontario was interrupted by intense aircraft vibrations and a temporary loss of control after a rudder trim bolt became detached.

What happened

During a training flight near North Bay, Ontario, the crew of a Beechcraft King Air A90, registration C-FCGE, experienced an uncommanded right turn accompanied by light vibrations while cruising at 11,500 feet. The crew elected to divert to North Bay for a landing.

During the descent, the situation escalated significantly. At approximately 8,500 feet, the aircraft was subjected to severe vibrations that were powerful enough to physically displace the pilot's hands and feet from the controls. For roughly 30 to 45 seconds, the crew lost control of the aircraft. Once the vibrations ceased, the crew regained control, though the aircraft required constant, heavy left rudder input to maintain coordinated flight. The aircraft landed safely at North Bay with no injuries.

The investigation

Investigators examined the rudder trim system and discovered that the hardware connecting the rudder trim actuator push/pull rod to the rudder trim horn was missing. The investigation focused on three potential causes for the hardware's disappearance: that it was missing during takeoff, that it fell out during flight, or that it broke in flight.

While the investigators could not definitively prove how the bolt left the assembly, they noted that a fatigue fracture was the most likely scenario. They also examined the operator's parts supply and found that while most hardware met specifications, one bolt was non-conforming and several others showed signs of previous use, contrary to company policy. Additionally, the investigation highlighted that the Illustrated Parts Catalogue (IPC) for the King Air 90 provided confusing and inconsistent descriptions regarding the specific hardware required for this assembly.

Findings

  • The primary cause of the incident was the detachment of the hardware securing the rudder trim actuator to the rudder trim tab horn.
  • The loss of this hardware allowed the rudder trim tab to flutter or become fixed in a position that forced the rudder to the right, necessitating heavy left rudder compensation.
  • Contributing factors included a lack of clear, consistent detail in the manufacturer's parts catalogue regarding the required assembly components.
  • The potential use of a non-conforming or substandard bolt during a previous installation may have contributed to the hardware failure.

Probable cause

The hardware securing the rudder trim actuator to the rudder trim tab horn became detached, causing rudder trim tab flutter and subsequent loss of control; the investigation also noted that confusing parts catalogue descriptions and the possible use of non-conforming hardware may have contributed to the failure.

Related events

Same operator

Frequently asked questions

What happened in the 1997-03-18 Department of Transport accident near Aircraft Services Directorate, CA?

A training flight in Ontario was interrupted by intense aircraft vibrations and a temporary loss of control after a rudder trim bolt became detached.

What aircraft was involved and where did it happen?

The accident on 1997-03-18 involved a Department of Transport, operated by Government of Canada, at Aircraft Services Directorate, CA.

What was the probable cause of the accident?

The hardware securing the rudder trim actuator to the rudder trim tab horn became detached, causing rudder trim tab flutter and subsequent loss of control; the investigation also noted that confusing parts catalogue descriptions and the possible use of non-conforming hardware may have contributed to the failure.

Loading the flight search…