Overview

During my time across drone assembly and later repair, I identified and resolved a high-frequency, flight-critical failure affecting the Kite Automatic flight test system.

The issue was causing a 30–50% first-pass failure rate on affected FCO batches, significantly impacting production flow, repair workload, and confidence in flight-critical electronics.

By combining hands-on repair insight, manufacturing observation, and cross-functional validation, I led a root cause analysis that uncovered a systemic assembly sequence issue. I then implemented a new quality inspection step, updated torque and assembly instructions, introduced a dedicated diagnostic test flow, and delivered operator training to prevent recurrence.

The Problem

Our Kite Automatic Quality Test (first-pass flight verification) showed a consistently high failure rate of 30–50% on specific FCO batches, leading to:

• High daily replacement rate of FCO flight control PCBs

• Increased rework load in repair operations

• Long debug cycles (≈45 min full test loop per unit)

• Misclassification of failures as component defects

• Reduced manufacturing confidence in flight-critical electronics

The issue was treated as a hardware defect problem (“swap FCO”), masking a deeper systemic cause.

Root Cause Discovery

While performing a routine repair, I observed that after installing the FLATPot (power conversion module), previously torqued FCO mounting fasteners required additional tightening to reach specification.

This indicated that a later assembly step was altering the mechanical state of the FCO PCB.

Investigation revealed:

• The FCO is mounted to a plastic baseplate using mixed fastener types (screws + nut/washer studs)

• The FlatPot installation introduces additional structural fasteners into the same stack-up

• These fasteners apply a different torque profile and load path

• This induces subtle PCB bending after initial torque validation

• The IMU (highly sensitive to mechanical strain) outputs inconsistent flight data under deformation

This created a latent mechanical distortion not detectable in the initial assembly step.

Validation

To validate the hypothesis, I initiated a cross-functional investigation with software and flight control engineers.

We:

• Extracted a dedicated 5-minute FCO-specific flight test from the full 45-minute Kite Automatic test

• Ran controlled comparisons on affected units before and after rework

• Analysed IMU telemetry, vibration signatures, and flight stability metrics

Results confirmed:

• Units consistently failed prior to correction

• The same units passed after re-torquing FCO fasteners post FlatPot installation

• Telemetry showed improved IMU stability and reduced vibration artefacts

This confirmed a mechanically induced flight control degradation rather than a component failure.

Solution Implemented

I led the implementation of a corrective and preventative quality improvement process:

1. Assembly Process Correction

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

• Updated torque sequencing instructions to maintain correct PCB load conditions

• Clarified ambiguous torque guidance for plastic-threaded fasteners

2. Diagnostic Acceleration

• Extracted a dedicated FCO test step from the full flight test sequence

• Reduced debug cycle time from ~45 minutes to ~5 minutes for targeted investigation

• Improved fault isolation efficiency in repair workflows

3. Operator Training

• Delivered shop-floor training session explaining root cause and correct assembly sequence

• Standardised understanding of mechanical sensitivity in flight-critical electronics

• Reduced reliance on “swap FCO” as default troubleshooting method

4. Cross-Functional Integration

• Collaborated with software engineering to integrate test isolation into internal testing branches

• Aligned with flight control engineers to validate IMU behaviour through telemetry analysis

Design Improvement (System-Level Fix)

Beyond process correction, I identified a structural design vulnerability in the mounting architecture.

Current design allows mechanical coupling between unrelated assembly stages, creating unintended PCB stress.

Proposed redesign direction:

• Chassis-based PCB mounting system

• Slide-in / plug-in (motherboard-style) architecture

• Mechanical isolation between structural load paths and electronics

• Controlled alignment features to eliminate deformation risk

This shifts the system from process-dependent reliability to design-in robustness.

Impact

Early validation and rollout indicate:

• First-pass yield improvement expected toward ~80% on affected builds

• Significant reduction in FCO replacement frequency in repair workflow

• Elimination of this failure mode as default diagnostic assumption (“swap FCO”)

• Reduction in diagnostic cycle time (~45 min → ~5 min for isolated testing)

• Improved engineering understanding of assembly-induced flight stability issues

• Shift from reactive component swapping to root-cause manufacturing engineering

Key Takeaway

This work demonstrated that a perceived electronics failure was actually a mechanical assembly interaction problem affecting flight control performance.

By combining repair insight, manufacturing observation, and cross-functional validation, I helped transition the organisation from component-level troubleshooting to system-level reliability engineering.