Common Quality Issues During the Pilot Run

Before you commit to mass production, the pilot run is the last step before giving the green light for mass production. While your prototypes may have looked great and your design files might be locked, producing 20, 50, or even 100 units often reveals issues that were not seen during previous validation builds. 

The pilot run is where everything gets put to the test using the mass production tools, processes, and materials. Even small issues, like slightly warped parts or unclear work instructions, can cause major delays and quality problems at scale if left unresolved.

In this blog, we’ll walk through the most common quality issues discovered during the pilot run. These range from product-related defects to assembly inefficiencies and supply chain mismatches. The goal isn’t just to catch problems, but to fix them before they grow costly in mass production.

Assembly Fit and Interference Problems

One of the most common and frustrating issues uncovered during a pilot run is when parts don’t fit together the way they should. Even if your CAD files were perfect and your prototype seemed fine, there are always new issues that arise during production that can cause problems. It’s like the saying, you don’t know what you don’t know. 

You might find that screw holes don’t line up, snap fits are too tight to engage properly, or cables aren’t long enough to reach their connectors once everything is in place. Hinges might bind, buttons may stick, or components that were supposed to slide in smoothly now require force or rework. These issues often arise because tolerances stack up across different components, and the impact isn’t obvious until you assemble the full product in larger batches.

Perhaps the most frustrating part is when you have two parts that are within spec and the correct tolerance, but they are unable to be assembled together. This should have always been found during design for manufacturing (DFM), but these issues do happen. 

The good news is that the pilot run is designed to expose these kinds of problems. The pilot run gives your engineering and production teams a chance to validate every mechanical connection and make sure the product can be assembled efficiently and repeatedly. 

To resolve these problems, you may need to revise part designs, adjust tolerances, modify tooling, or update your assembly process. The goal is to ensure that everything fits together consistently so your production team can focus on speed and quality, not constant troubleshooting.

Cosmetic Defects

Cosmetic defects are another common issue that shows up during the pilot run. Even if the parts are dimensionally correct and the product works as intended, surface flaws can hurt your brand and lead to costly rework or customer complaints. These cosmetic defects can also be the most costly if it can not be reworked since you have already fabricated the part and then coated it. 

Typical cosmetic defects include sink marks, flow lines, scratches, scuffs, blemishes, inconsistent finishes, paint defects, and color mismatches. These issues can stem from a variety of sources: incorrect mold temperature, poor mold polishing, handling errors, packaging design flaws, or even part ejection from the tool. In metal components, inconsistent brushing or anodizing can create noticeable variation from unit to unit.

The pilot run production is when you start seeing enough parts to assess surface quality across a small batch, not just a single perfect prototype. It’s your chance to identify patterns, determine whether the defects are isolated or systemic, and fine-tune your process before those issues scale up.

Fixing cosmetic issues may involve adjusting mold parameters, updating surface treatments, redesigning packaging to protect parts during handling, or establishing clearer visual inspection standards. The key is to align your internal team and your suppliers on what “acceptable” looks like, so cosmetic quality is consistent and repeatable in full production.

Functional Failures or Inconsistent Performance

The pilot run is the first time you truly see how well it performs across a batch of units. This is often when functional issues appear that weren’t obvious during prototyping or low-volume testing. While one or two units might have worked perfectly fine, building 50 or more can reveal inconsistencies that affect user experience or overall reliability.

Common functional problems include buttons that aren’t as smooth as predicted, moving parts that stick or feel inconsistent, electronics that respond unpredictably, or motors and batteries that underperform. Sometimes the root cause is component variability, such as different tolerances or specs across batches from your suppliers. Other times it’s an integration issue: parts that technically meet spec but don’t work together as expected under real-world conditions.

These problems can be especially frustrating because they may not appear on every unit, making them hard to solve. For example, a 5% failure rate might seem small, but at scale, that’s 500 defective units in a 10,000-unit run.

During the pilot run, it’s critical to perform functional tests on every unit and track issues in detail. Use this data to refine your test protocols, update your assembly process, and tighten component specifications. By resolving performance inconsistencies now, you prevent costly returns and reputational damage down the line.

Final Assembly Bottlenecks

Even if every part is within spec and the product functions well, the pilot run often reveals issues on the assembly line that kill output. These bottlenecks usually show up when your team is trying to build dozens of units under near-real production conditions, highlighting inefficiencies that weren’t obvious during prototype builds.

Some common signs of assembly bottlenecks include inconsistent assembly times, confusion over the build order, tools that don’t quite fit the workspace, or steps that require excessive manual adjustment. These slowdowns don’t just reduce throughput—they also increase the chance of errors, especially if operators are forced to make judgment calls without proper instructions or fixtures.

For example, if workers are unsure how tightly to fasten a screw, or if sub-assemblies don’t clearly align, you might see over-torqued parts, cosmetic damage, or inconsistent mechanical performance. Bottlenecks can also be caused by a lack of jigs and fixtures, unclear work instructions, or inadequate training.

Addressing these issues during the pilot run is essential. This is your opportunity to optimize the build process by developing standard operating procedures (SOPs), creating assembly aids, and validating takt times. A well-designed assembly process ensures that quality is built into each step and that your team is ready to ramp up confidently when mass production begins.

Packaging and Handling Defects

Packaging is often treated as an afterthought during product development, and it’s often forgotten about until the last minute. Even if the product is perfect coming off the line, poor packaging or handling can lead to scratches, dents, deformation, or contamination before it ever reaches the customer.

During the pilot run, you might notice parts getting damaged when they’re moved between stations, stored on racks, or placed into temporary trays. Final units may rattle in the box, shift during transit, or get scuffed from rubbing against other components. These issues are especially common with metal housings, coated surfaces, or products with exposed lenses, displays, or polished finishes.

Many of these problems stem from incomplete packaging design, like using the wrong materials, missing protective layers, or skipping drop tests. Others are process-related, such as workers stacking trays incorrectly or rushing during boxing and sealing.

The pilot run is your chance to identify these weak points. It’s the first time the full production and packing flow is tested end-to-end, from final assembly to outbound logistics. Use this phase to refine your packaging materials, redesign trays or inserts, and build clear handling procedures into your work instructions.

Well-designed packaging doesn’t just protect the product—it also reflects your brand’s quality and reduces costly damage-related returns once units hit the market.

Inconsistent Quality Control and Testing

Quality issues aren’t always the result of a bad part; they’re often the result of inconsistent inspection and testing practices. During the pilot run, many teams realized that their quality control processes aren’t clearly defined, aren’t followed consistently, or are missing altogether for certain steps in production.

You might discover that some units go through full functional testing while others don’t. Or that visual inspections vary depending on who’s performing them. Measurements might be taken on some dimensions but skipped on others. Without a standardized approach, good units can get flagged as bad, and worse, defective units can slip through unnoticed.

This lack of consistency usually stems from unclear test procedures, a lack of training, or missing inspection tools like gauges, fixtures, or properly calibrated equipment. It may also result from teams rushing to meet build deadlines without sufficient documentation or alignment on what “pass” and “fail” actually mean.

The pilot run is the perfect time to build out your inspection protocols and test plans. You should define critical-to-quality checkpoints, establish acceptable tolerances, and train operators on exactly what to look for. Whether it’s cosmetic, dimensional, or functional, every unit should be checked against the same criteria using the same methods.

By locking down your quality control processes during the pilot run, you reduce variation, increase confidence in your production output, and ensure that your first mass production batch meets expectations right out of the gate.

Supplier Component Variation

Even when your product is well-designed and your internal processes are dialed in, inconsistencies in supplier components can lead to unexpected quality issues during the pilot run. At this stage, you’re no longer building one prototype; you’re assembling dozens of units, often with parts pulled from different production batches or vendors. That’s when variation starts to show.

You might notice color mismatches between plastic parts, slight size differences in connectors, or inconsistent performance in off-the-shelf electronics. Fasteners might have different thread tolerances, or gaskets from different suppliers may compress differently. These seemingly small differences can have a major impact on fit, appearance, or functionality, especially in tight-tolerance or visually exposed areas.

This kind of variation usually isn’t due to one-off defects. Instead, it’s a sign that component specifications weren’t clearly defined, or that the supplier’s quality control isn’t aligned with your requirements. During the pilot run, it becomes obvious when two batches of "identical" parts don’t actually behave the same.

Solving this requires more than just spot-checking. It involves tightening part specifications, standardizing approved vendors, and possibly performing incoming inspections for critical components. If multiple suppliers are used for the same part, they should all meet the same testing and cosmetic criteria before parts are accepted into your line.

Catching these issues during the pilot run allows you to build consistency into your supply chain before mass production begins, saving time, reducing rework, and preserving your product’s quality and brand reputation.

What to Do When You Encounter These Issues

The pilot run exists to expose issues, so encountering problems is not a failure. It’s a necessary part of the process. The key is how you respond. Fixing problems at this stage is far less costly than discovering them during mass production or, worse, in the hands of your customers.

Here’s a structured approach for handling pilot run issues effectively:

1. Document Every Issue in Detail

Start by capturing everything. Whether it’s a dimensional deviation, a cosmetic defect, a functional failure, or an assembly inefficiency, document it. Take photos, record test results, and save rejected units when needed. Include which station or process the issue occurred in and how frequently it appears.

This documentation becomes the foundation for troubleshooting, communicating with your supplier, and updating internal documentation later on.

2. Categorize and Prioritize

Not all problems are created equal. Categorize the issues into different types, such as cosmetic, mechanical, functional, packaging, or process-related. Then prioritize based on severity and impact:

• Critical: Prevents product from functioning or shipping.

• Major: Affects performance, aesthetics, or user experience.

• Minor: Doesn’t impact performance but could hurt brand perception.

This helps your team (and your supplier) focus resources on the most urgent problems first.

3. Conduct Root Cause Analysis

Once you've prioritized the top issues, dig into why they’re happening. Is it a design flaw? A tooling tolerance issue? A handling problem? A supplier deviation?

Methods like 5 Whys, Fishbone Diagrams, or Failure Mode and Effects Analysis (FMEA) can help identify the root cause, not just the symptoms. Your contract manufacturer may also have their own protocols for root cause analysis so ask to review their processes so you can align your investigation accordingly.

4. Collaborate Closely With Your Supplier

Every supplier has different internal processes for dealing with pilot run feedback. Some may run internal corrective action reports (CARs), others may escalate issues through project engineering teams or quality managers.

Don’t assume the response is automatic. Initiate a meeting to review the issues together, walk through the findings, and align on next steps. Ask questions like:

• How do you normally respond to pilot run issues?

• Will you be updating SOPs, jigs, or tooling?

• What timeline do you expect for fixes?

• Will we receive updated samples before the next run?

A transparent and responsive supplier will help you close the loop quickly and proactively.

5. Update Your Documentation

Once fixes are in progress or completed, make sure your own files reflect those changes:

• Revise CAD files and drawings for dimensional updates

• Update SOPs, assembly instructions, and inspection criteria

• Amend the Bill of Materials (BOM) if alternate parts are needed

• Record test procedures and pass/fail thresholds clearly

This ensures that the next build, whether another pilot batch or full production, starts from a clean slate with the latest information.

6. Re-Validate Key Fixes

Don’t take fixes at face value. If tooling was modified, if components changed, or if process steps were updated, you need to re-test those changes. This might mean building a smaller follow-up batch or doing a targeted sample review.

Even minor adjustments can introduce new variables. Your goal is to confirm that each fix actually resolves the issue without introducing new ones.

7. Treat It as a Learning Opportunity

The pilot run isn’t just a checkpoint; it’s an opportunity to strengthen your product and your supplier relationship. You’ll learn more about how your contract manufacturer operates, how fast they respond, and how well they communicate.

This experience can guide how you collaborate during future builds and identify which processes you might need to own internally versus rely on your supplier for. If something feels misaligned now, it's better to address it before the stakes get higher.

Conclusion: Quality Issues During the Pilot Run

The pilot run is a part of the transition from development to mass production. It’s not just about producing a few extra units; it’s a critical checkpoint where hidden issues finally surface. From part tolerance problems to cosmetic flaws, assembly inefficiencies, and inconsistent testing, the pilot run gives you the data you need to refine both your product and your process.

Catching and fixing these issues now is far less costly than dealing with failures during mass production. But to do it effectively, you need a structured approach, clear documentation, and close collaboration with your contract manufacturer. Every supplier has different processes in place, so the best thing you can do is stay engaged, ask the right questions, and work together to lock down a build that’s repeatable and reliable.

When treated with the right level of attention, the pilot run becomes more than just a milestone; it becomes a launchpad for scalable, high-quality production.