As aviation enthusiasts and professionals, we often daydream about the ideal aircrafts for our local airlines. Imagine Philippine Airlines with Boeing 787-10s instead of A330-300s, or Cebu Pacific utilizing Airbus A350-900s for flights to America’s West Coast. While cost, range, fuel economy, capacity, and upkeep may seem like the key determinants, the decision is actually far more intricate. Allow me to provide a glimpse into how airlines determine the best fit for their fleet.
The selection process is quite intensive given the multitude of variables to assess. It goes far beyond merely reviewing specs listed on official airline websites; it requires an in-depth analysis of how the aircraft aligns with the airline’s strategic goals, intended destinations, objectives, routes, and targeted markets.
The paramount consideration lies in how an aircraft caters to the airline’s specific needs. This comprehensive analysis from Leeham News and Analysis, comparing the 787 and the A350, provides an understanding of why an airline might choose a seemingly less preferred aircraft.
Fuselage
The choice of fuselage cross-section sits at the core of differences between aircraft. It not only determines cabin width but also impacts the weight and drag of the fuselage.
The fuselage’s weight is primarily dictated by its outer surface area. Ever since World War II, airplane fuselages have adopted “stressed skin” designs, wherein the fuselage skin bears the loads. This skin is bolstered against buckling by vertical frames and horizontal longerons (the longitudinal profiles affixed to the skin, also referred to as stringers).
Weight
Given the same technology and dimensions under aircraft certification rules, fuselages usually weigh the same. A larger fuselage surface area directly equates to greater weight.
When analyzing the 787-10 and the A350-900, a disparity in fuselage dimensions is noticeable. The 787 fuselage has a width of 5.77m and a height of 5.97m, whereas the A350’s fuselage is 5.96m wide and 6.09m high.
This suggests that for each fuselage unit length, the surface area of the 787 fuselages is 2.5% smaller. If both fuselages boast identical cabin lengths, the difference might appear constant, but it isn’t.
As the fuselage diameter expands, the nose and tail areas also increase. The nose and tail taper at a certain rate due to aerodynamic considerations. Therefore, a larger diameter implies a lengthier nose and tail, equating to a more significant fuselage surface area. Interestingly, Airbus is currently contemplating using the extended tail of the A350 to accommodate additional cabin components.
Drag
Next in line is the impact of air resistance or drag. A fuselage with a larger diameter tends to generate increased drag. It’s important to note that the frontal area or pressure drag doesn’t necessarily come first, especially given its negligible impact on a modern airliner.
The dominant form of drag an airliner experiences at cruising speed is skin friction drag. This kind of drag originates from the air friction against the aircraft’s exterior surface. More fuselage skin invariably translates into more drag.
Remember that this discussion isn’t about medium or long-term objectives. It’s about exploring the implications of a wider A350 cabin that enhances comfort for economy class passengers. The differences, indeed, are significant.
The rest of the aircraft
Let’s shift our focus to other aspects of the aircraft. A weightier fuselage requires a bigger wing and more potent engines to maintain the same level of operational efficiency. Consequently, a larger wing and engine demand bigger tail surfaces (assuming the fuselage length remains unchanged).
Therefore, the aircraft equipped with the more commodious fuselage will register a higher empty weight and increased drag, given the same passenger load capacity.
Under standard conditions, this holds true. However, one could contend that this doesn’t necessarily apply when comparing the 787 and the A350.
One could reasonably assert that, with the exception of the range difference, the conditions are indeed equivalent. The construction methodologies employed for the 787 and A350 are notably akin.
The variations between the aircraft are indiscernible, given that one employs barrel-based carbon composite fuselage sections, while the other uses panel-based sections.
Moreover, there seems to be negligible operational discrepancy between the 787’s predominantly electrical system architecture and the A350’s traditional system structure.
Similarly, the wing designs bear resemblance. Both feature high aspect ratio composite wings (differing by less than 1%), capable of adjusting their shape in-flight using movable spoilers/flaps. Both also employ Fly-By-Wire systems for load alleviation.
The disparity in fuselage design considerably outweighs the minor differences in composite construction or other aircraft building techniques.
Medium range versus long range
This analysis hasn’t yet considered the considerations associated with designing an aircraft for medium-range (considered here as 6,400nm) versus long-range.
The long-range aircraft has to lift off with a greater quantity of fuel. Therefore, if both aircraft carry the same payload, the one designed for longer range will have a higher empty weight (accounting for the weightier fuel load) and a higher take-off weight (the sum of empty weight, payload, and fuel).
The longer-range aircraft also demands a larger wing and more robust engines to attain the increased take-off weight within the same airstrip length.
To sum up, the A350 8,000nm features a more sizeable fuselage, wing, and engines. When carrying the same payload across identical routes, all of these aspects contribute to increased drag and consequently, higher fuel consumption.
This outcome is partially attributable to the A350’s longer-range design, but it also stems from the A350’s less compact packaging.
Economic consequences
A heavier and larger aircraft brings about more than merely a spike in fuel consumption.
In the past, fuel was deemed the pivotal expense during the acquisition of an aircraft. While it remains crucial, its importance is now equally matched by crew size and fee costs (the charges levied by nations and airports for utilizing their air transport services).
Differences in crew costs between aircraft like the 787 and A350, which have similar cabin sizes, are primarily influenced by flight crew expenses. Within an airline, flight crew costs remain uniform for aircraft having equivalent capacity, maximum weight, and range. However, if an aircraft type exhibits superior capabilities in any of these areas, the flight crew receives higher compensation.
The size of the aircraft establishes the fees for utilizing airports and airways. The Maximum Take-Off Weight (MTOW) is the parameter that defines aircraft size. Consequently, fees for larger and long-range aircraft would be steeper due to their elevated MTOW.
Maintenance costs represent the final aspect of the Cash Operational Costs (COC, excluding the aircraft’s capital costs). Both the 787 and A350 are modern composite aircraft, implying their airframe maintenance schedules, and consequently, costs, are similar.
Dissimilar engine sizes are necessitated due to variances in aircraft size and capabilities. The take-off thrust of the 787-10 engine is 76klbf, while the A350’s is 84klbf. The A350’s Rolls-Royce Trent XWB has a 2.3t greater engine mass compared to the 787’s Trent 1000. An escalation in engine thrust and size equates to higher engine maintenance costs.
And to conclude
This should provide a sense of the complexities entailed in how airlines plan their fleet. Not to mention the separate dimensions of finances and marketing. Hence, comparing fleet selection between airlines like PAL, a full-service airline, and Cebu Pacific, a low-cost carrier, isn’t feasible. Full-service carriers generally operate over long to ultra-long distances. Branding and market positioning also play a significant role.
For now, it’s best to believe that the airline’s fleet planners and management are adept at their job. It’s not only a question of image but also one of viability and profitability, especially in the current economic climate.
First love never dies. I fell in love with airplanes and aviation when I was a kid. My dream was to become a pilot, but destiny led me to another path: to be an aviation digital media content creator and a small business owner. My passion for aviation inspires me to bring you quality content through my website and social accounts. Aviation is indeed in my blood and blog!
