Hi Gents,

I hope you are doing well.

out aircraft B1900 D experienced a sudden over-torque on the left engine during the takeoff roll at indicated airspeed of approximately 90Kts. The torque on the left engine reached to 5000 lbs, creating asymmetric thrust. The flight crew maintained control of the aircraft and prevented it from veering off the runway by reducing power on the right engine to maintain the centerline. During the second attempt, both engines were brought back to flight idle.

Upon returning to the apron, engineers inspected the left engine and found the inside part of the torque adjusting screw broken (the part of the screw inside the clevis as highlighted in red arrow). No damage was noted on the clevis or the beta arm.

According to our technical service, the broken flight blade adjustment screw likely caused the Beta lever to travel to an unusual forward position when transitioning to the flight range, despite the aircraft not lifting off, which contributed to the over-torque event.

It should also be noted that the flight crew encountered an issue during engine start: the propeller on the left engine failed to come out of feather. The PIC attempted to resolve the issue by advancing the propeller lever, but the problem persisted. He then cycled the propeller between feather and taxi positions to excite the feather valve and release the propeller from feather. This occurred prior to taxi.

From my understanding, this failure could occur if the screw remained in contact with the beta arm when reverse was selected on a previous flight due to a malfunctioning ground solenoid (maybe) , or if the screw had been weakened over time by cyclical stresses caused by a delayed response of the ground idle solenoid.

I kindly request a technical assessment based on your expertise..

Thank you in advance.