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Mechanical error resulting from faulty propellers from the manufacturer.Human error in the responsible storing of the propellers.
Understand and identify the location of UAS, if any people or property were involved or affected, and then, mitigate any hazards (fires, spinning props, etc) Then without anyone touching anything in the crash site, documentation is needed and most important. It seemed with this specific report, documentation was minimal, which makes it harder for those not included in the flight to understand what happened. Documentation done? If so, call for help if needed, and remove batteries. Next in the sequence is inspecting the drone, and gathering pieces. In this specific scenario the broken props, arms, and sensor were found and gathered.
There was no external damage to the environment, the reporting requirements were as follows: A crash report to the UAS dispatch, and a SATT Safety Report.
Impacts: Loss of M300 availabilityFinancial impact: Aircraft repair, part replacementLoss of confidence on reliability of M300 props or how they are handledActionsAircraft grounding - investigationReview maintenance recordsDocumentation from the eventPolicy ChangesMore intense preflight inspectionMore in depth maintenance records/investigationTeaching proper handling of drone equipment
Lucas Toppe, Aidan Tottori, and Hunter Hall
Background and Context
Date: 12:30 P.M on 4/16/2025
Location: Purdue Wildlife Area
Parties Involved: Anestis Tsagris (PIC), Cameron Perry (VO)
Nature of the crash: Prop failure, loss of stabilization and Multi-motor control. Possibly escalated by original sheared prop interacting with other props.
System: DJI Matrice 300C
Payload: Zenmuse P1 - 2
Root Cause Analysis
According to the UAS Dispatch M300-C maintenance report, the UAS underwent propeller replacement eight days prior to the crash. The maintenance report states that maintenance was conducted IAW prescribed policy. Although this seemingly points to human error as the cause of the crash, we believe that mechanical failure was probably the root cause.
Given the information found within the testimony of the crash report, as well as the flight data, it is hard to conclude that human error during the operation was the primary cause of the crash. The PIC engaged in moderate throttle input (63%) at the 14 second mark of the screen recording attached to the crash report. Suddenly, the input increases to 85% at the 15 second mark. Although this input change is seemingly significant, it is well within DJI’s expected range of operation. The sudden stress on the propellers caused by the throttle increase almost certainly caused the shearing; however, the M300-C props should certainly be able to tolerate such stress.
Given this, during the operation, there is no reason to believe that the flight team acted contrary to policy. Additionally, environmental factors had negligible effect on the operation according to the METAR given on the Crash Report. Regulatory failures also have no relevance to the crash.
This leaves mechanical failure as the root cause. As previously referenced, the M300-C underwent recent propeller replacement. Though this evidence seemingly absolves mechanical failure as a root cause, we assert the contrary. Maintenance and testing inherently involves handling. Handling carries the potential for human error. If the propellers were improperly stored, this could have caused fractures in the propeller that ultimately broke off and caused the crash.
Given the evidence, either one of two factors (or both) caused the crash:
Crash Dynamics
The aircraft logs the message “Flight mode changed to Motor Stop Landing” at 10.6 seconds into the flight at an altitude of 46.6 feet - this would mark the point where one motor’s voltage dropped significantly and rapidly due to the lack of load on the motor from the propeller disassembling or otherwise detaching itself from the motor. A tenth of a second later, the aircraft displays the message “Aircraft Propulsion system error. Forced Landing. Manually control the aircraft and land in an open area.” This is consistent with the requirements to activate the Three-Propeller Emergency Landing unique to the Matrice 300. As outlined in the White Paper DJI published, the aircraft will switch to this mode within 200ms of an anomaly being detected - 100ms to detect the fault, and another 100ms to act on it. “In this phase, the aircraft could drift horizontally up to 30m; vertical movement could reach up to 5 meters.”
Given the mode changes as well as the documentation, we can infer that the aircraft detected the motor speed anomaly from the entire propeller failing to produce lift (not damaged but simply sheared off or otherwise removed), and attempted to enter three motor landing mode but was unable to accomplish this as a result of the detached propeller striking the others in flight and resulting in the loss of thrust from multiple motors. This is reflected as the aircraft rapidly cycles through flight modes and errors, seemingly attempting to regain control of itself in one of its failure modes but failing and pushing the aircraft towards the ground faster than it would normally fall if it was disarmed.
From 11.5 to 11.7 seconds, I sampled what the yaw rate was, and it was -1265 degree/second which would suggest that the drone attempted to recover itself but overshot due to lack of control authority.
Subsequent calculations from 11.3 to 12.9 seconds yielded a Δyaw average = -765.5/1.6s = -478 deg/s, indicating a significant yaw rate somewhat in line with the Matrice recovery mode.
Post-Crash Response and Consequences
Post Crash Response: There are several steps to take when initiating a post-crash response.
Reporting: It is important that if you experience a crash, you must report to the needed team/organization/people. Since this was a Purdue owned drone, they must follow the reporting regulations required. (If there was damage to items outside the drone over $500, or a person, the FAA needs a report).
Impacts, actions, and policy changes:
Recommendations
This does not seem like a human error issue, therefore, the recommendations need to target the items/drone itself, or the handling thereof.
It is hard to really make a good recommendation that could ultimately fix what happened here. This is because you cannot really pin this on the party involved. There was an inspection, maintenance record performed, and initial testing of the ability to fly the M300. It seems that this falls back on prop failure/the manufacturer.
Ultimately, if it came down to making a recommendation, we believe that during the replacement of the props in maintenance, the inspection of the props should be more strict. Also, if it were possible, under a controlled environment, the props could be put under a proper stress test to ensure no failure in flight.
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