Accident Overview
On August 17, 2021, at approximately 1715 eastern daylight time, a Diamond Aircraft Industries DA-42, registration N215BN, was substantially damaged during a forced landing near Bellefontaine, Ohio. The flight instructor and student pilot were not injured. The aircraft was operating under Title 14 Code of Federal Regulations Part 91 as an instructional flight.
Flight and Power Loss
The flight instructor was conducting a short-field takeoff from runway 7 with the student pilot. During the climb after takeoff, the right engine experienced a complete loss of power, followed by the left engine losing partial power, with about 30% of available power remaining. The instructor executed a forced landing onto a grass field near the departure end of the runway. The airplane sustained substantial damage to the wing spar and landing gear.
Maintenance History
Logbook records indicated that the left and right engine fuel feed pumps (FFP) were installed on the day of the accident, at a tachometer time and total time of 3,138 hours. The FFPs were replaced as part of a 600-hour time-limited component change. The operator did not perform, and was not required to perform, a test flight after completing this maintenance.
Engine Control Unit Data
Engine control unit (ECU) data from the left engine on the accident day recorded 14 canceled engine start messages over about 57 minutes. Approximately three hours later, four canceled start messages were logged over about one hour, followed by another canceled start about three hours after that. The right engine ECU recorded 16 canceled engine start messages over a similar period, followed by two low rail pressure messages, which were the last messages recorded. According to the airplane manufacturer's service representative, the numerous start attempts were consistent with air in the system resulting from fuel system maintenance.
Postaccident Examination
Postaccident examination revealed that both engine exhaust pipes failed the testing protocol specified in Federal Aviation Administration airworthiness directive (AD) 2018-CE-002, which applies to Diamond Aircraft Industries airplanes. The AD described an unsafe condition of uncommanded engine shutdown during flight due to failure of the propeller-regulating valve caused by hot exhaust gases from fractured exhaust pipes. The operator did not and was not required to perform a maintenance test flight after completing maintenance.
Engine Test Run Findings
In preparation for an engine test run, the operator replaced both propellers, repaired the damaged landing gear, and reinstalled the engine exhaust pipes from the accident engines. After the accident, the left engine FFP bolt was found seated, but the right engine FFP bolt was not seated. Several start attempts on both engines were unsuccessful. After priming, only the left engine started and operated normally. Once the right engine FFP bolt was seated, that engine started and operated normally. The operator's maintenance personnel stated that they did not change the position of the right engine's FFP bolt during installation on the accident day.
Fuel Feed Pump Bolt Details
The FFP bolts were not manufactured with retaining hardware to prevent backing off from their seat. The bolts carried no labeling indicating that in-service adjustment was not permitted. According to the engine manufacturer, the FFP bolt is torqued to 12 nanometers during manufacture and sets the unit's pressure reducing valve. If the bolt is not completely seated, air can enter and/or fuel can escape from the unit. The engine manufacturer stated that the bolt should not be removed during any maintenance or bleeding action, and that the repair manual describes the proper bleeding and pressure measurement process. The manufacturer had not tested an FFP with a bolt in a position similar to that found on the accident airplane's right engine, but noted that fuel leakage through the bolt threads could reduce fuel supply to the high-pressure pump, affecting rail pressure.