Overview

During drone assembly and subsequent repair operations, I identified and investigated a recurring, flight-critical failure affecting the Kite Automatic flight-test system.

Affected FCO batches showed a 30–50% first-pass failure rate, driving unnecessary PCB replacements, rework and lengthy diagnostic cycles.

Through hands-on investigation, I traced the issue to a mechanical interaction between assembly stages: installing the FlatPot power conversion module altered the clamping condition of the previously torqued FCO PCB, introducing mechanical distortion that affected IMU behaviour.

I led the corrective investigation and coordinated cross-functional validation, then introduced an updated torque sequence, a mandatory post-installation inspection, a dedicated diagnostic test and operator training. I also identified a longer-term opportunity to remove the underlying mechanical vulnerability through a revised mounting architecture.

The Problem

The Kite Automatic flight-test process showed a 30–50% first-pass failure rate on affected FCO batches, resulting in:

• Frequent FCO flight-control PCB replacements

• Increased repair and rework workload

• Diagnostic cycles of approximately 45 minutes per unit

• Failures being treated as component defects rather than assembly-related issues

• Reduced confidence in flight-critical electronics

The default response was to replace the FCO, often without identifying why the failure had occurred.

Root Cause Discovery

During a routine repair, I observed that installing the FlatPot required additional tightening of FCO mounting fasteners that had already been torqued to specification.

This indicated that a subsequent assembly operation was changing the mechanical condition of the PCB after its initial torque verification.

My investigation identified an interaction between the mounting arrangements:

• The FCO PCB is mounted to a plastic baseplate using a combination of screws and nut/washer studs.

• Installing the FlatPot introduces additional structural fasteners into the same assembly.

• The resulting change in fastener loading alters the PCB's clamping condition.

• This introduces mechanical distortion after the initial assembly check.

• The distortion affects the mechanically sensitive IMU, resulting in inconsistent flight-test behaviour.

The key finding was that the assembly sequence could introduce a latent mechanical condition after the PCB had already passed its initial torque check.

Validation

I coordinated a cross-functional investigation with software and flight-control engineers to test the hypothesis and isolate the failure.

The investigation involved:

• Extracting a dedicated five-minute FCO diagnostic test from the full 45-minute Kite Automatic test sequence

• Comparing affected units before and after corrective re-torquing

• Reviewing IMU telemetry, vibration signatures and flight-stability indicators

The before-and-after comparisons showed that affected units failed prior to correction and passed after the FCO fasteners were re-torqued following FlatPot installation. Telemetry analysis also indicated improved IMU stability and reduced vibration artefacts.

These results supported the conclusion that assembly-induced mechanical distortion, rather than an inherent PCB component defect, was responsible for the observed failure behaviour.

Solution Implemented

I drove the corrective actions across assembly, diagnostics and operator training to address both the immediate failure mechanism and the way it was investigated.

1. Assembly Process Correction

• Introduced a mandatory inspection and re-torque step after FlatPot installation

• Updated torque sequencing instructions to maintain the intended PCB clamping condition

• Clarified torque guidance for fasteners engaging with plastic threads

2. Diagnostic Acceleration

• Isolated a dedicated FCO test from the full flight-test sequence

• Reduced the targeted diagnostic cycle from approximately 45 minutes to five minutes

• Enabled faster fault isolation without repeatedly running the complete test sequence

3. Operator Training

• Delivered shop-floor training explaining the root cause and revised assembly sequence

• Standardised the inspection and re-torque procedure

• Reduced reliance on default FCO replacement as the first troubleshooting response

4. Cross-Functional Integration

• Worked with software engineering to integrate the isolated diagnostic test into internal testing branches

• Coordinated with flight-control engineers to assess IMU behaviour using telemetry

• Connected repair observations with manufacturing-process improvements and engineering validation

Design Improvement (System-Level Fix)

The corrective process addressed the immediate failure mechanism, but the investigation also exposed a vulnerability in the mounting architecture: separate assembly operations could interact mechanically and introduce unintended PCB stress.

I identified a longer-term design direction to reduce dependence on assembly sequence and operator intervention:

• A chassis-based PCB mounting arrangement

• A slide-in, plug-in architecture inspired by motherboard interfaces

• Separation of structural load paths from sensitive electronics

• Controlled alignment and mounting features to minimise deformation risk

This remains a proposed design direction rather than a validated redesign. Its objective is to move from process-controlled reliability towards inherent mechanical robustness.

Impact

The investigation and corrective actions delivered several improvements:

• Initial failure rate: 30–50% on affected FCO batches, establishing the scale of the original problem

• Diagnostic cycle: reduced from approximately 45 minutes to five minutes for targeted FCO investigation

• Fault isolation: demonstrated that corrective re-torquing could restore passing test behaviour on affected units

• Assembly quality: introduced a mandatory inspection and re-torque step following FlatPot installation

• Troubleshooting: shifted the response away from default component replacement towards root-cause investigation

Early rollout indicated a target of approximately 80% first-pass yield on affected builds. This should be treated as a target or preliminary estimate until supported by sufficient post-change production data.

Key Takeaway

A recurring flight-control test failure initially treated as an electronics defect was traced to a mechanical interaction between assembly stages.

By combining hands-on repair insight with mechanical reasoning and cross-functional validation, I identified the failure mechanism, implemented corrective process and diagnostic improvements, and established a direction for a more robust mounting architecture.

The project demonstrated how mechanical design, assembly sequence and verification methods directly influence the reliability of an integrated mechatronic system.