What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
N5152U was operating under part 135 rules doing forest fire watch patrol on 08/09/19 in the mountains near Prospect, OR when the pilot experienced a total sudden engine failure at about 3:30 pm PDT. Pilot reported sudden violent shaking of airplane so severe that instruments could not be read, and started emergency engine shutdown procedures for an emergency landing. Pilot pulled mixture and engine stopped firing, but propeller kept turning slowly. Pilot found clearing in forest marsh area and made power off emergency landing. Aircraft was substantially damaged but remained upright and both pilot and passenger were unhurt. NTSB released airplane for recovery from mountain clearing and operator was instructed not to perform any maintenance or part removal except for radios.
Aircraft was sent to operator's hangar for quarantine and storage pending engine removal.
During recovery operator's director of maintenance (dom) removed cylinder rocker box covers without authorization from FAA or NTSB and found #1 cylinder had both pushrods FAR down in pushrod tubes. Broken engine camshaft at least is suspected. NTSB has authorized teardown of engine at manufacturer, and follow up amendment of this report is planned after teardown is completed.
NTSB has also authorized a calibration and accuracy test of the oil temperature indicating system in follow up to the accident.
As the FAA filed it
N5152U WAS OPERATING UNDER PART 135 RULES DOING FOREST FIRE WATCH PATROL ON 08/09/19 IN THE MOUNTAINS NEAR PROSPECT, OR WHEN THE PILOT EXPERIENCED A TOTAL SUDDEN ENGINE FAILURE AT ABOUT 3:30 PM PDT. PILOT REPORTED SUDDEN VIOLENT SHAKING OF AIRPLANE SO SEVERE THAT INSTRUMENTS COULD NOT BE READ, AND STARTED EMERGENCY ENGINE SHUTDOWN PROCEDURES FOR AN EMERGENCY LANDING. PILOT PULLED MIXTURE AND ENGINE STOPPED FIRING, BUT PROPELLER KEPT TURNING SLOWLY. PILOT FOUND CLEARING IN FOREST MARSH AREA AND MADE POWER OFF EMERGENCY LANDING. AIRCRAFT WAS SUBSTANTIALLY DAMAGED BUT REMAINED UPRIGHT AND BOTH PILOT AND PASSENGER WERE UNHURT. NTSB RELEASED AIRPLANE FOR RECOVERY FROM MOUNTAIN CLEARING AND OPERATOR WAS INSTRUCTED NOT TO PERFORM ANY MAINTENANCE OR PART REMOVAL EXCEPT FOR RADIOS.
AIRCRAFT WAS SENT TO OPERATOR'S HANGAR FOR QUARANTINE AND STORAGE PENDING ENGINE REMOVAL.
DURING RECOVERY OPERATOR'S DIRECTOR OF MAINTENANCE (DOM) REMOVED CYLINDER ROCKER BOX COVERS WITHOUT AUTHORIZATION FROM FAA OR NTSB AND FOUND #1 CYLINDER HAD BOTH PUSHRODS FAR DOWN IN PUSHROD TUBES. BROKEN ENGINE CAMSHAFT AT LEAST IS SUSPECTED. NTSB HAS AUTHORIZED TEARDOWN OF ENGINE AT MANUFACTURER, AND FOLLOW UP AMENDMENT OF THIS REPORT IS PLANNED AFTER TEARDOWN IS COMPLETED.
NTSB HAS ALSO AUTHORIZED A CALIBRATION AND ACCURACY TEST OF THE OIL TEMPERATURE INDICATING SYSTEM IN FOLLOW UP TO THE ACCIDENT.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.