The Hidden Challenges of D Checks: Why HeavyMaintenance Pushes Airlines to the Limit

When most people think of air travel, they picture the journey: the boarding gate, the cabin crew, and the flight itself. Few realize that behind the scenes, airlines carry out some of the most complex maintenance tasks in the industrial world. At the pinnacle of these efforts lies the D check—the heaviest, most comprehensive inspection an airliner will ever undergo in its lifetime.

Performed roughly every six to twelve years, a D check requires the aircraft to be taken out of service for weeks, sometimes months. The airplane is essentially stripped down to its skeleton, with every component inspected, tested, or replaced. While vital for safety and airworthiness, D checks come with daunting challenges that affect airlines, maintenance providers, and regulators alike.

The Nature of a D Check

Unlike routine line maintenance or lighter A and C checks, a D check is all-encompassing.

The aircraft’s interior is removed, wiring and hydraulics are inspected, landing gear and

engines are serviced, and the fuselage and wings are combed for cracks or corrosion. By

the time it’s completed, tens of thousands of labor hours may have been spent and

millions of dollars invested.

This scale sets the stage for the unique challenges that D checks present.

1. The Financial Burden

The cost of a D check can run into the tens of millions of dollars, depending on the aircraft

type and condition. For a large widebody like a Boeing 777 or Airbus A330, the cost may be

so high that airlines instead opt to retire the aircraft early rather than proceed.

• Example: In 2020, as the COVID-19 pandemic crushed demand, airlines such as Delta Air Lines and American Airlines chose to retire older Boeing 757s, MD-88s, and Airbus A330 200s rather than face upcoming D checks. The cost of heavy maintenance simply outweighed the value of keeping those jets in service.

2. Downtime and Fleet Planning

An aircraft undergoing a D check can be out of service for up to two months. For airlines,

this isn’t just about the lost use of the airplane—it’s about schedule disruptions, increased

leasing costs for replacement capacity, and reduced operational flexibility. Fleet managers

must plan years in advance to ensure they can cover the downtime without compromising

service.

• Example: Southwest Airlines, with one of the world’s largest Boeing 737 fleets, carefully staggers heavy checks to avoid too many aircraft being grounded at once. A single miscalculation could ripple through its tightly scheduled point-to-point network.

3. Skilled Labor Shortages

Carrying out a D check requires highly trained and licensed aircraft maintenance

engineers. Yet, the aviation industry faces a global shortage of skilled labor, particularly in

heavy maintenance. This scarcity drives up costs and creates bottlenecks, especially when

multiple airlines are competing for the same pool of qualified technicians.

• Example: In 2023, Lufthansa Technik warned that the MRO industry faced a shortage of thousands of skilled technicians worldwide, threatening to slow down turnaround times for D checks.

4. Surprises in Aging Aircraft

While checklists exist for every inspection, the most disruptive findings are often

unexpected. Corrosion hidden beneath insulation, fatigue cracks in structural

components, or obsolete wiring can add weeks and millions of dollars to a project.

• Example: In 1988, Aloha Airlines Flight 243 suffered explosive decompression due to undetected fuselage fatigue. Though not directly tied to a missed D check, the incident pushed regulators to tighten inspection standards for aging aircraft, making modern D checks even more rigorous.

5. Regulatory Oversight

Airworthiness authorities such as the FAA and EASA oversee every aspect of a D check.

Compliance requires meticulous documentation and adherence to evolving directives and

service bulletins. While this oversight ensures safety, it adds complexity and administrative

workload to an already massive task.

• Example: After the Boeing 737 MAX grounding, regulators worldwide increased scrutiny not only on aircraft design but also on how airlines and MROs document and execute heavy checks.

6. Supply Chain Constraints

Even if an issue is discovered early, sourcing the necessary replacement part can be a

challenge. Structural components, specialty fasteners, or interior fittings may have long

lead times—especially for older aircraft models where OEM support is limited.

• Example: During the pandemic, airlines reported long delays in sourcing interior panels and landing gear parts for older Airbus A320s and Boeing 767s, sometimes extending D check timelines by weeks.

7. Facilities and Logistics

Not every maintenance, repair, and overhaul (MRO) provider has the capacity to conduct a

D check. Widebody aircraft in particular require massive hangars, heavy-duty tooling, and

advanced logistical coordination.

• Example: United Airlines outsources some of its widebody heavy checks to Ameco Beijing, one of Asia’s largest MROs, to save on costs and take advantage of facilities purpose-built for D checks.

8. Technology Integration

Newer digital inspection tools, drones, and predictive maintenance systems promise to

reduce surprises in D checks, but they don’t eliminate them. Many aircraft undergoing D

checks are older models not originally designed with modern predictive analytics in mind.

• Example: easyJet has experimented with using drones to speed up heavy maintenance inspections. While useful for surface scans, drones cannot replace hands-on structural disassembly required in a D check.

Industry Trends: Avoiding the D Check

Faced with these challenges, some airlines make a strategic decision: retire the aircraft

rather than invest in a D check. Others seek cost savings by outsourcing heavy

maintenance to lower-cost regions such as Asia, Eastern Europe, or Latin America.

• Example: After the pandemic, Qantas retired its Boeing 747-400 fleet earlier tha planned, citing the cost of heavy maintenance and low demand. Meanwhile, carriers like LATAM send aircraft to South America’s growing MRO hubs to take advantage of lower labor costs.

Conclusion: More Than Maintenance

A D check is far more than just a maintenance milestone—it’s a strategic decision point.

Airlines must weigh the cost of extending an aircraft’s life against the benefits of retiring

or replacing it. Regulators must ensure that safety is never compromised despite financial

pressures. MRO providers must adapt to labor shortages, supply chain challenges, and

technological transitions.

Ultimately, the D check embodies the balancing act at the heart of modern aviation:

keeping aircraft safe, reliable, and compliant while navigating economic realities. For

passengers, it’s a reminder that the flight experience begins long before boarding—it begins

in the hangars, where teams of engineers work tirelessly to ensure every journey is safe.

Want to read about how this complex work is tracked and invoiced appropriately? Let me

suggest: https://www.logisticsmro.com/post/cost-capture-and-invoicing-in-mro-and-

heavy-maintenance