Amateur-built PA-12 N406Z accident near Douglas, Wyoming

Probable cause

A loss of power due to fuel exhaustion as a result of the pilot’s failure to calibrate the fuel flow indicator.

NTSB analysis

The pilot was performing a Phase 1 flight test in the airplane following the installation of a new engine. The pilot reported that before departure the engine ran rough, with a loss of about 250 rpm while operating on only one of the two electronic magnetos. He dismissed the anomaly as the engine functioned normally with both electronic control unit (ECUs) on or on the other ECU. The pilot then flew for 2 hours on 40 gallons of fuel. The pilot switched tanks halfway through the flight. About 20 minutes before the accident, the pilot saw one of the multi-function displays flicker and then 20 minutes later a total loss of engine power occurred. Both ECUs indicated they were off and the pilot’s three attempts to restore power to the engine by recycling the ECUs were unsuccessful. The pilot initiated a slip maneuver to descend quickly from the base leg and rolled out into a three-point attitude over the runway. The airplane landed hard, both main landing gear axles failed, and the airplane nosed over and came to rest inverted. The vertical stabilizer and rudder were substantially damaged. The pilot noted that the axles were likely insufficient to carry the loads of the airplane during normal operations and sheared during the hard landing.

Postaccident examination of the airplane and engine did not reveal any preimpact mechanical anomalies that would have precluded normal operation. The pilot reported that his multi-function display flickered and that he received indications that ECU 1 was off and ECU 2 was disconnected after the loss of power; however, all the ECU connections were secure and both ECUs functioned normally during a postaccident engine run.

Performance computations showed that the airplane would have consumed about 39 gallons of the 40 gallons of fuel onboard at the beginning of the flight. Thus, it is likely that the loss of engine power was due to fuel exhaustion. The displayed fuel consumption (in gallons per hour) by the ECU was likely incorrect and may have been off by several gallons as the pilot had not calibrated the fuel flow, which was required by the ECU manufacturer after installation. The ECU operation would not have been influenced by or affected the system’s fuel management during the accident flight, as the systems were not connected.

Text from the NTSB. Open the NTSB docket for WPR24LA205 for the full record.