On August 17, 2021, about 1715 eastern daylight time, a Diamond Aircraft Industries DA-42, N215BN, was substantially damaged when it was involved in an accident near Bellefontaine, Ohio. The flight instructor and student pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.
The flight instructor was conducting a short-field takeoff from runway 7 with the student pilot. During the climb after takeoff, the right engine lost all power, which was followed by the left engine losing partial power (about 30% of available power remained). The flight instructor performed 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.
Logbook records showed that the left and right engine fuel feed pumps (FFP) were installed on the day of the accident with an airplane 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 upon completion of this maintenance.
Engine control unit (ECU) data for the left engine on the day of the accident recorded 14 canceled engine start messages during a period of about 57 minutes. About 3 hours later, four canceled engine start messages were recorded during a period of about 1 hour, which were followed by another canceled engine start message about 3 hours later. The right engine ECU recorded 16 canceled engine start messages during a similar period, which were followed by two low rail pressure messages, which were the last two messages recorded. According to the airplane manufacturer’s service representative, the numerous engine starts were consistent with air in the system from the maintenance that was performed on the fuel system.
Postaccident examination of the airplane revealed that the left and right engine exhaust pipes failed the testing protocol included in Federal Aviation Administration airworthiness directive (AD) 2018-CE-002, which affected Diamond Aircraft Industries airplanes. The AD described “the unsafe condition [of] uncommanded engine shutdown during flight due to failure of the propeller-regulating valve caused by hot exhaust gases coming from fractured engine exhaust pipes.” The operator did not and was not required to perform a maintenance test flight upon completion of maintenance.
In preparation for an engine test run, the operator replaced both airplane 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, and the right engine FFP bolt was found not seated.
Several start attempts of the left and right engine were made, all of which were unsuccessful. The left and right engines were then primed, but only the left engine started and operated normally. After the right engine FFP bolt was seated, the right 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 when the FFP was installed onto the right engine on the day of the accident.
The FFP bolts were not manufactured with retaining hardware to prevent the bolts from backing off from their seat. The FFP bolts did not have any labeling indicating that in-service adjustment of the bolt was not permitted.
According to the engine manufacturer, the FFP bolt is torqued to 12 nanometers during manufacture. The bolt sets the unit’s pressure reducing valve, and, if the bolt is not completely seated, air can enter and/or fuel can escape from the unit. The engine manufacturer also stated that the FFP bolt should not be removed during any maintenance or bleeding action and that the repair manual describes the process for bleeding the fuel system and measuring pressure. The engine manufacturer further stated that it had not tested an FFP with a bolt in a similar position as that found on the accident airplane’s right engine, but, if fuel leaked through the bolt threads, there might not be enough fuel to the high-pressure pump, which would affect rail pressure.