How Boeing Builds a 737 in Just Nine Days: Inside the Fastest Jet Assembly Line in Aviation

Building a commercial jet in just nine days is an extraordinary achievement. Boeing began producing the 737 in 1968, and by 1998, it was assembling only seven aircraft per month—most of the work done manually. That same year, production of the 737 Next Generation (NG) increased to 14 jets per month. In 1999, Boeing revolutionized its manufacturing process, cutting build time to 11 days. With the launch of the 737 MAX, the timeline was streamlined even further—to just nine days.

Today, Boeing’s 737 production line is one of the fastest in aviation history. By early 2019, this accelerated pace enabled the company to produce up to 52 aircraft per month—a dramatic leap from earlier decades. The efficiency was driven by a need to fulfill a backlog of over 4,000 orders and to stay competitive with Airbus, which plans to reach 75 aircraft per month by 2026.

At Boeing’s Renton, Washington facility, the assembly process runs on a moving production line. Fuselages arrive pre-built from Wichita, Kansas, and the build begins with the installation of wiring, plumbing, and avionics. Next, the wings, tail, and landing gear are attached. By day six, the aircraft is powered for testing; engines are installed on day seven, and final system checks are completed by day nine. The process concludes with painting and a customer walkthrough inspection.

However, this rapid pace has raised concerns. The National Transportation Safety Board (NTSB) linked the January 5, 2024, Alaska Airlines incident—where a door plug detached mid-flight—to incomplete documentation during the moving assembly process. In response, Boeing implemented a “move-ready” approach, ensuring that aircraft only advance along the line once critical tasks are fully completed.

From Garage-Style to Conveyor Assembly

Before this shift, Boeing used a traditional “garage-style” method, where the aircraft remained stationary while teams rotated in to complete each phase. But with thousands of orders piling up, Boeing needed a faster solution. Today, the 737 moves along a conveyor belt at roughly two inches per minute, passing from one team to the next. If a team can’t finish its tasks in time, the work is documented for the next group to complete.

Boeing 737 Assembly Timeline

Days 1–4: Structural and Interior Installation

Day 1–3: Interior Systems

Pre-built fuselages arrive by train from Wichita, Kansas.
Workers install insulation, hydraulic systems, electrical wiring, and avionics.
WiFi antennas and dorsal fins are added if requested by the airline.

Day 4: Structural Assembly

Wings and horizontal stabilizers are attached using precision laser alignment.
Vertical tail fin and landing gear are installed.
The aircraft begins to resemble a complete jet.

Days 5–9: Testing, Engine Installation, and Final Checks

Day 5–6: Cabin and System Testing

Rear galleys, lavatories, water tanks, and waste compartments are installed.
Flight control systems are connected and tested.
Power is turned on for the first time, enabling landing gear and subsystem checks.

Day 7–8: Engine Installation and Diagnostics

The aircraft is lowered onto its own wheels.
Engines are mounted and connected to hydraulic and electrical systems.
Flight control surfaces (flaps, slats, rudder, elevator) undergo diagnostics.
Cockpit systems are tested for integration and functionality.

Day 9: Final Inspections

The customer conducts a walkthrough inspection.
The aircraft is rolled out for engine run-ups, taxi tests, and its first flight.
Painting is completed in the following days, but by day nine, the jet is fully assembled.

Lessons from the Alaska Airlines Incident

The January 5, 2024, blowout on Alaska Airlines Flight 1282 exposed critical flaws in Boeing’s documentation and quality control. Investigators found that four bolts meant to secure the door plug were missing, and the issue had not been recorded during assembly. Boeing’s revised “move-ready” system aims to prevent such oversights by requiring completion of key tasks before advancing the aircraft.

Balancing Speed, Safety, and Market Pressure

Despite ongoing safety concerns, Boeing continues to push for faster production of its 737 MAX jets. As of mid-2025, the company faces a backlog of over 4,700 unfilled orders for the aircraft. With Airbus planning to ramp up production of its A320neo family to 75 aircraft per month by 2026, Boeing must accelerate its output to maintain market share and meet customer demand.

Financially, speed is essential. The faster a jet is built, the lower the labor and overhead costs. Boeing’s nine-day assembly timeline is a strategic move to reduce expenses and reassure customers and shareholders that it can deliver aircraft on schedule.

However, quality concerns persist. FAA audits in 2024 uncovered non-compliance issues in Boeing’s manufacturing process, prompting increased oversight and a mandated safety action plan. To regain control over quality, Boeing acquired Spirit AeroSystems—the subcontractor responsible for the faulty door plug involved in the January 2024 Alaska Airlines incident. This acquisition is part of Boeing’s broader effort to restore trust and improve safety standards across its supply chain.

Competitive Pressure from Airbus

Market competition adds another layer of urgency. Airbus, Boeing’s primary rival, delivered 602 A350 aircraft last year and currently produces about six per month. The company plans to increase A350 output to ten per month by 2026, despite ongoing supply chain challenges. Meanwhile, Airbus is also expanding its A320neo production capacity, aiming to reach 75 aircraft per month by 2027.

Boeing cannot afford to fall behind. In July 2025 alone, Airbus delivered 67 aircraft, while Boeing delivered 48. The gap in output underscores the pressure Boeing faces to ramp up production without compromising safety or quality.

The Bottom Line: Speed vs. Precision

The financial stakes are high. The longer a plane remains on the production line, the more man-hours and costs accumulate. Boeing’s accelerated timeline is designed to minimize these expenses while keeping pace with global demand. But recent incidents have shown that speed without precision can be costly—not just in dollars, but in reputation and regulatory consequences.

Boeing’s race to build the 737 faster than ever is driven by intense market demand, competitive pressure, and financial necessity. Whether the company can balance efficiency with safety will determine the future of its most iconic jet—and its standing in the global aviation industry.

Sources: AirGuide Business airguide.info, bing.com, msn.com, simpleflying.com, faa.gov