Why Are The A340 Engines So Small
The total thrust from four engines on the A340 is comparable to that of the two A330 engines.
During the conceptual design phase of what would become two of the popular wide body jets, Airbus discovered that North American carriers wanted twin-engine aircraft, primarily for their inter-regional operations. On the other hand, airlines in the Asia-Pacific region needed a four-engine aircraft for long-haul operations across the Pacific. Airbus simultaneously developed the A330 twin-jet and the A340 quad jet to cater to both markets.
So, why are the Airbus A340s engines so small?
Before answering this question, it is important to understand the difference between the two comparable variants of the A330 and A340 aircraft: the A330-300 and the A340-300. The similarities and differences between the two types are provided in the table below.
From the above table, it is evident that both the Airbus A330-300 and A340-300 share the same fuselage length and wingspan. The A340-300 is heavier and has a greater MTOW. The extra weight drove the need for an additional center rear landing gear. The A340 also has a greater operational range due to the larger fuel tanks and capacity than the A330-300.
Particularly interesting is that the A330 engines are much larger, similar to those used on Boeing 747-400s and 767-400s. Conversely, the A340 engines are similar in size to those used on most single-aisle aircraft, including the Airbus A320 family and the Boeing 737s.
What is also noteworthy is that the total thrust achieved by two engines on the A330-300 is comparable to the resultant thrust from four engines on the A340-300. In order to serve two different markets and customers' demands, smaller engines were purposely selected for the A340s.
Airbus’ design philosophy
Airbus based its design philosophy for the two models very specific to the market, thereby serving medium-to-long haul North Atlantic and inter-regional routes with the twin-engine A330s and the ultra-long-haul flights over water with the quad-engine A340s. While the A340s featured smaller engines, they were more reliable and fuel-efficient on long overwater routes.
If the aircraft loses one engine, it is only 25% of the total power lost, as in the case of the A340. Moreover, the aircraft can continue to fly over waters with three operational engines. On the other hand, losing one engine on a twin-jet, such as the A330, means half of the total power is lost. While flying within the ETOPS range for the type is still safe, the pilots most certainly deviate from their course and perform an emergency landing.
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