• As carriers work to extend the lives of widebody fleets amid continued delivery delays and capacity constraints, a new obstacle is grounding aircraft: engine parts.
• At the centre of the disruption is Pratt & Whitney’s PW4000, specifically, the 112-inch fan variant powering early Boeing 777s.

United Airlines, the largest operator of this engine type, is now experiencing mounting difficulties in keeping its PW4000-powered 777s flying, due to limited MRO capacity and an increasingly scarce pool of replacement parts.

“United is having trouble keeping its PW4000-powered 777s in the air,” Courtney Miller, Managing Director at Visual Approach Analytics, wrote in a recent post sharing the findings of their latest Aircraft Intelligence Monthly report.

“This is a specific disruption affecting the ageing 777 fleet, too large for operators to ground, yet too small to attract major long-term investment from suppliers.”

The fleet in focus

The PW4000 series is a longstanding widebody engine, powering multiple aircraft types across several decades. Three major fan sizes were produced: 94-inch (used on A310, 747, 767, MD-11), 100-inch (A330-200/300), and the largest 112-inch variant, the latter fitted exclusively to early-build 777-200, -200ER and -300 models.

It is this 112-inch version, now out of production, that is causing the most acute concern. According to Visual Approach’s data, more than 70 such aircraft are still active globally, with United Airlines operating the largest fleet, 47 aircraft in total. Other carriers affected include ANA, Korean Air, Asiana, and Jin Air.

These aircraft were among the earliest 777s built, with many now over 25–30 years old. Yet they remain in use, driven by limited twin-aisle availability, especially in the North American market.

The core challenge lies in the mismatch between fleet size and aftermarket support. The number of remaining PW4000-powered 777s is too high to ignore operationally, but too small, compared to newer engine families, to justify significant new investment from OEMs or third-party suppliers.

“This is proving a unique challenge,” Miller notes. “The fleet remains large enough for United to rely on it, but too small for Pratt & Whitney or suppliers to invest heavily in long-term support.”

United’s difficulties reportedly began in late 2025, when the airline flagged parts scarcity and limited engine shop availability. According to the report, this forced the carrier to reduce utilisation of affected aircraft and reassign capacity from other fleets.

The strain is not isolated to United. As other operators rely on PW4000-powered aircraft, particularly in Asia, the broader impact on MRO networks and spare engine availability is growing. Maintenance providers are now juggling ageing engine needs alongside newer platforms, just as airlines push for extended service lives.

The report suggests that shop slot scarcity and high parts prices will likely continue into 2026, keeping availability tight and utilisation conservative.

“This is a classic case of the aftermarket lagging the operational demand curve,” one MRO industry executive told Air Cargo Week. “The PW4000 112-inch fan was always a niche variant—and as support declines, even airlines with strong in-house MRO are feeling the pressure.”

Cargo implications

While most of the affected aircraft are passenger-configured, some carriers may have been relying on older 777s for cargo uplift during peak seasons or for ad-hoc charter operations. The grounding or underutilisation of these aircraft could add further strain to tight widebody capacity, especially as e-commerce and time-sensitive logistics continue to drive demand across key lanes.

More broadly, the issue underscores a larger trend in the cargo sector: the fragility of aftermarket ecosystems supporting older aircraft types. As airframes outlive initial design expectations, engine and parts support must evolve—or risk leaving vital capacity grounded.

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