An analysis of five recent C-checks found total findings ranging from 840 to 1,635 discrepancies per aircraft. The aircraft with the highest number of findings generated nearly twice the workload of the lowest.

This is part of why every heavy maintenance visit begins with a plan.

Weeks before an aircraft enters the hangar, teams have to complete steps like:

• Assigning staff
• Ordering materials
• Allocating hangar space
• Establishing milestone schedules

These plans are necessary. A key challenge is that most maintenance teams build them around information they already have before the check begins, such as:

• Scheduled inspections
• Service bulletins
• Engineering orders
• Routine task cards

Historical data and previous maintenance visits allow organizations to estimate these requirements with a reasonable degree of confidence.

However, a significant portion of the actual workload remains hidden until the aircraft is opened and inspected.

There are several discrepancies that only get discovered after an inspection begins, such as:

• Corrosion
• Cracks
• Damaged structure
• Previous repair discrepancies

Once these findings are documented, non-routine task cards are generated, engineering becomes involved and the true scope of the maintenance visit begins to emerge.

This creates a gap between planned work and actual work.

Milestones are often built around the workload that is known. The aircraft, however, offers a bigger picture.

For example, structural corrosion is often discovered during heavy checks. What begins as a routine inspection can quickly become one of the most labor-intensive tasks on the aircraft.

This is because finding unexpected corrosion can cause maintenance teams to need:

• Extensive access
• Removal of surrounding components
• Engineering evaluation
• Repair fabrication
• Inspections
• Follow-up operational checks

In some cases, the impact extends far beyond the repair. Keel repairs, for example, may require the removal of hydraulic lines to gain access.

This means hydraulic operational checks can be delayed until those repairs are completed and the systems are restored. A single finding can affect multiple work groups and influence several milestone targets.

Maintenance organizations cannot wait until every inspection is complete before developing a schedule. Before an aircraft arrives at an MRO or repair shop, teams need to complete forecasting for elements like:

• Aircraft utilization
• Staffing requirements
• Parts procurement
• Customer commitments

For aging fleets, this challenge is often compounded by parts availability issues, as some components become increasingly difficult to procure because they’re no longer manufactured.

Aircraft entering the same maintenance program also do not always generate the same amount of work.

Multiple aircraft may share the same maintenance plans, but they often do not share the same history. Once an aircraft is opened up, inspectors and mechanics can discover:

• Years of operational stress
• Previous repairs
• Utilization history
• Aircraft age

These uncertainties are an unavoidable part of heavy maintenance. The question is how organizations learn from the surprises.

If the same corrosion, cracking or structural findings appear repeatedly across multiple aircraft, at what point do they stop being considered non-routine?

If a finding consistently appears during heavy maintenance visits, should it remain a surprise, or should it become part of future planning assumptions?

Some findings are unique to a particular aircraft. Others show up repeatedly across the fleet. Over time, those recurring findings begin to paint a clearer picture of what inspectors and mechanics are likely to discover during future visits.

No maintenance visit will ever be completely predictable. There will always be unknowns. However, the more we learn from previous checks, the better we become at recognizing the types of work likely to be discovered during future visits.

The goal is to make the next schedule better informed than the last one.

While aircraft inspections and maintenance will always reveal some conditions that cannot be fully predicted in advance, the variability can be significant even among aircraft undergoing the same maintenance visit.

Additionally, the number of findings alone does not determine schedule impact. Many discrepancies can be resolved quickly, while a single structural repair may require work like:

• Engineering support
• Parts procurement
• Invasive access
• Additional inspections
• Operational checks

The aircraft will always have the last word. The question is whether maintenance providers can listen closely enough to engage in predictive maintenance that keeps planes flying and keeps teams efficient.