A twinjet double-decker airplane does not exist primarily due to economic and design considerations in the aviation industry.

Economic Factors

1. Market Demand and Efficiency: Airlines have shifted towards operating smaller, more efficient twin-engine aircraft rather than large quadjets like the Airbus A380 or Boeing 747. This trend is driven by a preference for point-to-point travel over the traditional hub-and-spoke model, making smaller aircraft more desirable for frequent routes that can better match passenger demand.

2. Cost of Operation: Operating a double-decker aircraft generally incurs higher costs, particularly in fuel consumption. Twin-engine planes are more economical to operate due to lower fuel requirements compared to larger four-engine designs. The cost savings from using twinjets can be significant, prompting airlines to favor these models for their operations.

Design Challenges

1. Weight and Structural Limitations: A double-deck design adds considerable weight to an aircraft. This increased weight typically results in a smaller usable floor space on the upper deck, which can limit passenger capacity and revenue potential compared to single-deck designs.

2. Engine Performance Requirements: Designing a twin-engine aircraft that could safely operate with the size and passenger capacity of existing double-deckers presents engineering challenges, particularly regarding engine performance during critical flight phases like takeoff and landing. For instance, if one engine fails, a twinjet must still have enough thrust to maintain safe operation, which is more challenging at larger sizes.

3. Infrastructure Constraints: Double-decker aircraft require specific airport infrastructure, such as larger gates and boarding facilities, which limits their operational flexibility. This requirement further discourages airlines from investing in such aircraft, as not all airports can accommodate them.

Future Considerations

While there have been concepts and patents for a twin-engine double-decker aircraft (such as those filed by Airbus), no serious development has progressed beyond theoretical designs due to the aforementioned challenges and market dynamics. The current trend favors lighter, more efficient aircraft that can serve a wider range of routes without the limitations imposed by size and operational costs.

In summary, the combination of economic viability, design challenges, and changing market demands has led to the absence of twinjet double-decker airplanes in commercial aviation today.

References

1. Reddit - ELI5: Why Doesn’t a Twinjet Double-Decker Airplane Exist?
2. Simple Flying - Will We Ever See Another Double-Decker Plane?
3. Simple Flying - Airbus Double-Deck Twin-Jet
4. Infinite Flight Community - Will There Ever Be a Triple-Decker?
5. Airliners.net - Double-Decker Aircraft Discussion
6. YouTube - Double-Decker Aircraft
7. Wikipedia - Double-Deck Aircraft
8. Reddit - Explain Like I’m Five