Yellowstone Project

Yellowstone was a Boeing Commercial Airplanes project to replace its entire civil aircraft portfolio with advanced-technology designs. The term “Yellowstone” refers to the technologies; Y1, Y2 and Y3 refer to the aircraft themselves.

It matters to the 747 story because Y3 was the aircraft that was supposed to replace the 747 — and it was never built.

The technologies

• Composite aerostructures instead of aluminium as the primary structural material.
• More electric systems, reducing the hydraulic and pneumatic systems that had run large aircraft since the 1950s.
• More efficient turbofans — the Pratt & Whitney PW1000G geared turbofan, the General Electric GEnx, the CFM International LEAP and the Rolls-Royce Trent 1000.

The three aircraft, and what actually happened

Y1 — to replace the 737. Intended for the 100- to 200-seat market.

Outcome: never launched. Faced with the Airbus A320neo in 2011, Boeing chose to re-engine the 737 instead, producing the 737 MAX. The clean-sheet single-aisle Yellowstone envisaged has still not been built.

Y2 — to replace the 767, and possibly the 777-200. Y2 began as the conventional, highly efficient baseline alternative to the Sonic Cruiser, a project codenamed “Glacier”.

Outcome: built. Y2 became the Boeing 787 Dreamliner, covering the 220- to 320-seat market against the A330 and later the A350. It is the only Yellowstone aircraft that reached production, and it is where the composite structures and more-electric systems actually arrived.

Y3 — to replace the 777-300 and the 747. Intended for the 300- to 400-plus seat market, competing with the A380 and the largest A350s.

Outcome: never launched. Boeing instead re-engined and re-winged the 777 as the 777X, using 787-derived technology — including folding composite wingtips — rather than designing a new aircraft. The 747’s replacement, in practice, is a twin-engined 777.

What it says about the 747

Yellowstone is a useful lens on why the 747 ended. Boeing’s own long-range plan had the 747’s successor as a 300- to 400-seat aircraft, not a larger one. Even in the plan, the direction of travel was down in size and down in engine count.

The 747-8 went the other way, and sold 155 aircraft. The 787 — Y2, the smaller and more efficient aeroplane — sold in the many hundreds and took over the routes the 747 had flown.

The last 747 was delivered in January 2023. Y3, the aircraft meant to replace it, was never launched at all.