Call them customers of size (like Southwest) or passengers with a high body mass (like Air France), but one thing is for certain:  As airline passengers become larger, they are taking up more space on planes.  Traveling is uncomfortable enough as it is with consistent delays, lost luggage, and – most recently in Seattle – accidental gassing of passengers, without having to deal with the awkwardness of other passengers encroaching into seat space they did not purchase.  Of course, there is no need to blame only obese passengers; passengers wearing giant coats and passengers who have extremely broad shoulders, to name a couple, are also encroachers.  Most airlines keep quiet about their internal policies for addressing encroaching passengers, but a few are upfront about their procedures.  Air France, for example, lists the width of the aisles and onboard seating, stating tersely, “If your waist measurement exceeds this, you must reserve an additional seat.”  Southwest avoids the measurement standard, instead relying on the simple rule:  If you cannot lower your armrests, you need to purchase an additional seat.  JetBlue uses a different test:  “People who are unable to sit in the seat in the full upright position with the seat belt fastened” may not be allowed to fly at all.  Airlines that require large passengers to purchase an additional seat do not actually require the passengers to pay fully for it.  Air France offers a 25% discount to their high body mass passengers when they purchase two seats.  Southwest refunds the additional seat at the end of the trip.

At first glance, the policies established by the airlines may seem to resolve the problem, but anyone who has traveled knows that there are plenty of passengers who pass the tests described above but still take up extra space.  Your neighbor’s hips push into your seat a couple inches and you have to squeeze yourself into the opposite side of your seat to avoid the unwanted physical contact.  Moreover, as our nation becomes increasingly more politically correct, you might feel a lingering guilt about reacting strongly against the contact.  You look around at the other passengers as you lean heavily away from your large neighbor, and worry that they are thinking:  How rude of him to treat his neighbor as if being fat is somehow contagious!  Poor thing, she probably has a glandular problem. From the perspective of the large passenger, she may feel very uncomfortable knowing that she is taking up your space, but she cannot do anything about it…right?

Wrong.  What happens when someone trespasses on your property?  You can call the police and file a lawsuit for the resulting damage.  What happens when someone steps into your personal space at work?  You are legally protected to confront the person and can seek support from human resources.  It is inconsistent to fail in providing airline passengers similar recourse when another person infringes on their right to enjoy a full seat.  People who use public transportation might respond to such an argument by reporting the many uncomfortable experiences they have had on the subway or in a city bus.  There is an important difference between public transportation and airline travel:  As an airline passenger, you are paying for the rental rights to a specific seat on a specific plane.  Sure, on Southwest you have choice of your seat, but ultimately you have purchased a seat.  As a public transportation passenger, you are paying for the option to ride on a specific bus or train.  If one bus is packed, the choice is yours to push on in or wait for the next one to arrive.

Unlike public transportation passengers, when an airline passenger purchases a plane ticket, she is paying for two primary things:  the transportation from her point of departure to her arrival destination, and the quality of the transportation.  The quality of transportation varies, depending on whether she purchases a coach, business, or first class ticket.  The airline may offer snacks or individual television sets to improve its quality; however, the single-most significant component of the transportation quality is the airplane seat.  Airplane passengers are, essentially, extremely short-term tenants who rent the space in which they sit for the duration of the flight.  They do not just rent the seat itself; they rent an invisible box that includes the empty space from the seat to the ceiling and from the seat to the floor.  The armrests are divided in half, meaning that window- and aisle-seat passengers have one and a half armrests, whereas middle-seat passengers only have access to one arm rest (the sum of each half of an armrest they can access on either side).  If we visualize this abstract box, we can draw cubic inches that compose it.  When a passenger purchases a ticket, she is buying all of those cubic inches that compose her personal box.  The value of the cubic inches is calculated by the difference of the price of the ticket and the value of transportation.  For example, if a passenger purchases a ticket from San Francisco to New York City for $500 and the value of transportation is $250, then the value of her transportation quality, in sum, is $250.

Let’s assume away the value of snacks, drinks, and the tiny televisions that hardly work (their value is minimal), and assume that a passenger buys the rental rights to 100 cubic inches when she purchases a plane ticket.  That means that each cubic inch is worth $2.50 to her – not to the airline.  The airlines do not need to have these passengers buy an additional seat; rather, they need to facilitate transactions between passengers so that the encroaching passenger compensates her neighbor for the extent of encroachment.  The practical concerns can be easily resolved.  All the airlines need to do is include extendable rulers so that passengers can estimate the extent of the encroachment and address the transaction.  Worried that your new, giant hat will get crushed in the storage bins?  Looks like 5 cubic inches of encroachment.  Pay up the $12.50 to your neighbor.  The naysayers who will criticize the idea for its practicality problems or undoubted disputes that will arise should be reminded that we already go through a great deal of largely impractical airport practices:  We take off our shoes, we pay extra for our luggage, and we make airport restaurants filthy rich from all the food we buy over delays.  One more moment of awkwardness and one more swipe of the credit card will have a minor, marginal impact on the challenges of traveling today.