Fixed Costs, Variable Costs, and Why Airlines Keep Going Bankrupt

The Distinction That Explains Half of Corporate Finance

Every cost a business incurs falls into one of two buckets, fixed or variable, and understanding the split explains an enormous amount about why some industries are wildly profitable in good years and catastrophically unprofitable in bad ones, while others plod along steadily no matter what the economy does. A fixed cost is one that does not change with how much a company sells or produces, at least not in the short run. A variable cost is one that rises and falls directly with volume. Almost every real business cost is a mix of the two, but the ratio between them, called a company's cost structure, is one of the single biggest determinants of how risky that business actually is, and there is no better real world illustration of the concept than the airline industry, which has produced more corporate bankruptcies per dollar of revenue than almost any other major industry in modern history.

Fixed Costs, the Bill That Arrives Regardless

A fixed cost has to be paid whether a company sells one unit or one million units in a given period. For an airline, the biggest fixed costs are aircraft leases or ownership, pilot and crew salaries under long term labor contracts, airport gate leases, and maintenance obligations, all of which are essentially locked in months or years in advance and barely change whether a given flight departs with 40 passengers or 180. An airline that has committed to a fleet of aircraft and a flight schedule has committed to a large fixed cost base regardless of how many tickets it actually sells. This is different from a business like a landscaping company, where most of the cost, hourly labor and gas for the mower, only gets spent when a job is actually booked.

Variable Costs, the Ones That Scale With Volume

A variable cost rises and falls with how much a company produces or sells. For an airline, jet fuel is the clearest example, a plane burns roughly proportional fuel whether or not the seats are full, but catering, baggage handling costs, and credit card processing fees on ticket sales genuinely do scale with passenger count. For a manufacturer, raw materials are the classic variable cost, twice as many units produced means roughly twice as much raw material purchased. The key financial feature of a variable cost is that it protects a company in a downturn, if demand falls, variable costs fall right along with it, which limits the damage.

Operating Leverage, Why Airlines Are the Textbook Case

The ratio of fixed to variable costs in a business determines something called operating leverage, how much operating income swings for a given swing in revenue. A business with high fixed costs and relatively low variable costs, like an airline, has high operating leverage, meaning small changes in revenue produce large changes in profit, in both directions. When passenger demand rises even modestly above what the fixed cost base was built to support, almost every additional dollar of ticket revenue drops straight to operating profit, since the plane, crew, and gate are already paid for regardless. This is exactly why airlines can post enormous profits in strong years. But the same mechanism runs in reverse just as violently. When demand falls, whether from a recession, a fuel price spike, or an external shock, ticket revenue falls but the fixed costs, aircraft leases, crew contracts, gate fees, do not fall nearly as fast, and an airline can go from solidly profitable to burning cash in a matter of months. Combine that with the industry's typically heavy debt load used to finance aircraft purchases, and you get an industry where a relatively modest demand shock has repeatedly been enough to push major carriers into bankruptcy protection, a pattern that has repeated across multiple US carriers over the past several decades.

A Worked Example

Compare two hypothetical companies, both with 100 million dollars in revenue, 90 million dollars of total costs, and 10 million dollars in operating income. Aerowing Airlines has a cost structure that is 80 percent fixed, 72 million dollars of fixed costs and 18 million of variable. Greenfield Landscaping is the mirror image, 20 percent fixed, 18 million of fixed costs and 72 million of variable. Now assume revenue for both falls 15 percent to 85 million dollars, and variable costs fall proportionally with it.

The same 15 percent revenue decline pushes Aerowing from a 10 million dollar profit to a 2.3 million dollar loss, because 72 million dollars of its cost base did not move at all, while Greenfield stays comfortably profitable at 5.8 million dollars because most of its costs shrank right along with revenue. Neither company changed anything about how it operates. The entire difference in outcome comes from the cost structure alone.

The Break Even Point

Every business with fixed costs has a break even point, the revenue level at which total revenue exactly covers total costs, calculated as fixed costs divided by contribution margin percentage, the share of each revenue dollar left over after variable costs. A business with a high fixed cost base needs to clear a high break even point before it earns a single dollar of profit, but once it clears that point, extra revenue is extremely profitable, since most of the cost base is already covered. Understanding a business's break even point is the first step in understanding how sensitive it is to a downturn, and it is the reason experienced investors look closely at cost structure, not just revenue growth, before judging how risky a company actually is.

The Bottom Line

Fixed costs do not care how much a company sells. Variable costs do. The ratio between the two decides how violently a company's profit swings when the economy does not cooperate, and no industry teaches that lesson more reliably than the airlines.