Aircraft, an incredible feat of aerospace engineering, is humanity’s greatest attempt to conquer the skies. It is a complex piece of machinery with multiple forces acting to keep it airborne. On the other hand, it is the most valuable asset upon which the financial fortunes of airlines reside. Load factor plays a crucial role in the performance of an aircraft and airline profitability. In this article, we’ll focus on the load factor-what it is and why it is important.
Understanding load factor aviation
Load factor aviation may be interpreted differently- load factor (aeronautics) and an airline’s load factor. The aeronautical load factor basically explains the science behind aircraft maneuvering. On the other side, the airline’s load factor mostly has to do with the carrier’s revenue and measures the capacity utilization of its aircraft.
Both load factors are correlated and quintessential for an airline to maintain and sustain its operations. Let’s take a closer look at each load factor in detail.
1. Aeronautical load factor
While studying aerodynamic forces acting on aircraft, you’ll encounter an aeronautical load factor. This load factor aviation provides a mathematical and scientific explanation of the changes in the aerodynamics of a flight.
When an aircraft flies, four forces come into play, i.e., weight, lift, thrust, and drag. If these forces are imbalanced, they may affect the flight characteristics and compromise the structural integrity of an aircraft. The aerodynamic forces are subject to changes whenever the plane changes its velocity in any direction. Every maneuver results in an increase/decrease in load factor. But what is the load factor?
Simply put, the Load factor (n) is the ratio of lift generated by wings (L) to the gross weight of an aircraft (W). i.e. n = L/W
When a plane is flying in straight and level flight, it is pulled vertically downward by gravity and pushed vertically upwards by lift. Both lift and weight forces are equal and hence sustain the aircraft in flight. The load factor in this scenario is 1 g. But, the load factor doesn’t always remain the same and can be greater or less than one depending on aircraft maneuvers.
When does the load factor change?
The forces acting on the aircraft and the orientation of its vertical axis can increase or decrease the load factor.
When an aircraft makes a coordinated turn, the aerodynamic forces change, causing a change in load imposed on the aircraft. A steady turn is an unbalanced acceleration since the turning force causes the aircraft to turn continuously. An aircraft needs more lift to support the load put on the aircraft, which is higher than just the weight of the plane. In turning flights, more lift should be generated to support the weight, which makes the load factor greater than one.
Changes in bank angle lead to variations in the load factor. Mathematically,
n=1/cosϴ, where n is the load factor, and ϴ is the angle of the bank.
So, with a 0° angle of the bank, the load factor is 1; at 45°, it increases to 1.4G. In turn, with 60°, the load factor further increases to 2G.
Flying the aircraft ” the right way up” during the level flight makes the load factor +1. On the contrary, the ‘upside-down'(inverted) movement results in a load factor of -1.
How do changes in load factor impacts occupants onboard?
Both positive and negative load factors create differences for occupants of the aircraft. Pushing the stick forward when an airplane is flying straight may cause slight weightlessness on the part of the passengers. When the load factor drops below 1 G, i.e., zero or very small, all people onboard feel weightless.
But if the pilot moves the stick forward strongly, the lift will exert in the opposite direction to normal. This is the case of the negative load factor, which makes passengers feel they are upside down.
When the pilot jerks the stick back suddenly, the airplane climbs, creating a positive load factor. In such a scenario, all occupants will feel pressed down in the seats and heavier than usual.
Why is the load factor important in aircraft?
Every aircraft designer must meet minimum load factor limit criteria to get certification for their aircraft. While manufacturers attempt to make an aircraft as light as possible, they must make concessions in their design. The aircraft must be designed to tolerate a limited load factor without sacrificing strength or safety.
Pilots need to comply with load factor limits established for aircraft to ensure safety. Human beings have limited capacity to hold out against 1+ load factor, be it positive or negative. Civil aviation authorities prescribe the load factor limits an aircraft can attain without any structural damage. Each aircraft design has a load factor limit within which it must operate without damage. Operating outside the approved limits can compromise the structural integrity of the aircraft and jeopardize safety. Exceeding the load factor limits during a maneuver is an FAA violation.
- The FAA has established minimum standards for different types of aircraft catering to various operational situations.
- Transport category planes (large civil airplanes and helicopters): -1 to +2.5
- Normal category and commuter category planes: -1.52 to +3.8
- Utility category: -1.76 to +4.4
- Acrobatic category: -3.0 to +6.0
- Helicopters: -1 to +3.5
2. An airline’s load factor (passenger load factor)
The above-discussed load factor aviation is a scientific description of the lift-to-weight ratio. Now let’s dive a little into the load factor aviation that mainly deals with economic aspects of the air transport system.
The airline load factor or passenger load factor represents the proportion of available seats that have been sold out. Empty seats don’t bring in revenue, so airlines strive to make the most out of their expensive assets by filling all seats at high ticket prices.
Passenger load factor is a metric used in commercial aviation to assess the economic performance of airlines. Purchasing an aircraft requires a huge investment, and selling tickets is the only way to recover costs. Load factor indicates how efficiently airlines utilize their fleet of aircraft in the face of major capital outlays.
Passenger load factor calculation
The load factor measures the percentage of available seats purchased by passengers on flights during a given period. Generally, the load factor for a single flight can be calculated as follows:
Load factor=Number of passengers/number of seats
E.g., if an airline performs a flight carrying 150 passengers out of 180 seating capacity, its load factor is 83.33 % (150/180 x 100%).
The International Air Transport Association (IATA) publishes the industry-wide passenger load factor monthly as a part of the air passenger market analysis. You can calculate an airline’s load factor figure as follows:
Load factor=Revenue passenger miles (RPMs)/ Available Seat Miles (ASMs)
Revenue Passenger Mile (RPM) is the product of flying passenger numbers and miles on a flight. If 100 passengers fly 200 miles on a flight, it generates 100 x 200=20000 RPMs.
Similarly, available seat mile means one plane seat flown one mile, whether filled or not. An airplane having a seating capacity of 130 passengers generates 26000 ASMs upon flying 200 miles.
So, local factor= 20000/36000=0.769 or 76.9%
Break-even load factor
The Break-even load factor can be defined as a minimum load factor required by an airline to not make a loss on its flights. Beyond the break-even load factor, the airline can record a profit. The load factor at which the carrier will break even depends on its costs and expenditure. Major US carriers like Delta, American, United, etc. require a 72.5% -78.9% load factor to stay break-even.
High load factor vs. low load factor
The high load factor is often associated with growing airline revenue as many available seats are sold. As the airline is a capital- and asset-intensive industry, selling more seats helps to spread its fixed costs amongst flyers. A higher load factor reflects that the airline has utilized its aircraft capacity to carry more passengers. The more seats passengers occupy on flights, the higher will be the airline revenue.
The low load factor represents that the airline failed to fill its seats. Every flight seat is a perishable product. Once the aircraft takes off, airlines can never generate revenue from the seat flown empty on that particular flight. Airlines face a low load factor when they can’t get enough passengers to occupy seats on their aircraft. The low load factor indicates low-profit margins and poor performance on the part of airlines to generate sales.
While legacy or full-service carriers can sustain with slightly lower load factors, low-cost airlines don’t have that option. Operating on a low-fare business model, they must fill their aircraft to survive and remain profitable. Furthermore, they offer several unbundled travel-enhancing options to earn ancillary revenue, increasing with more onboard passengers.
One can look into load factor aviation from two different perspectives: economic and scientific. The scientific load factor aviation is the lift-to-weight ratio, whereas the passenger load factor aviation is the ratio of passenger numbers to available seats.