Cirrus Design Corp SR20 N389CP accident near Green Cove Springs, Florida

Probable cause

The fusing of an electrical cable from the No. 2 (standby) alternator with the throttle cable resulting in the flight crew’s inability to move the throttle control. Contributing to the accident was the failure of maintenance personnel to detect inadequate clearance and chafing of the Alternator No. 2 output cable against the throttle cable housing during the 100-Hour inspections.

NTSB analysis

During an instructional flight while in contact with a Federal Aviation Administration air traffic control facility, the student pilot reduced the throttle to descend with no response. The CFI took the controls and attempted several times to move the throttle control but was unable. The certified flight instructor (CFI) maneuvered the airplane toward a nearby airport, but was unable to maintain altitude due to the decreased engine rpm. During controlled flight while descending, the airplane impacted the tops of trees then impacted the ground. The CFI, whose hand was on the airframe parachute system handle at the point of tree contact, unintentionally fired the parachute at the moment of ground contact. The airplane then nosed over and the rear seat occupant broke the rear window using the emergency egress hammer. All 3 occupants exited the airplane. Further inspection of the engine compartment revealed the No. 2 alternator output cable was routed under the throttle cable, which is contrary to the routing when the airplane was manufactured. The throttle cable housing chafed thru the insulation of the Alternator No. 2 output cable causing arching and fusing both together, preventing movement of the throttle control. Review of the maintenance records revealed six discrepancies related to the No. 2 alternator and two discrepancies related to the throttle control in over a six month period. Two of the corrective action entries for the alternator issued involve removal and replacement of the data acquisition unit (DAU) and master control unit (MCU), while the corrective action for the throttle control was that it was lubricated. Between the date of the six discrepancies related to the No. 2 alternator and the two entries related to the throttle, the airplane was inspected a total of four times either in accordance with a 100-Hour or annual inspection. Inspection of the wiring of the alternator for condition and security is contained in the airplane's maintenance manual.

Text from the NTSB. Open the NTSB docket for ERA09LA062 for the full record.