From a health and safety standpoint, the FAA requires that passengers be able to evacuate the plane in 90 seconds with half of the exits blocked. As long as the passengers can get out in a simulated evacuation, the actual number of seats is of no regulatory consequence.

Although the risk of deep vein thromboses has met with media frenzy, the scientific evidence is not too convincing; business class passengers seem to have the same risk of a thrombotic event.

Many people ask me about infectious disease transmission on airplanes (I'm an epidemiologist and work in TB.) Yes, it is possible to catch TB on an airplane, but it is not a common source of TB transmission.

The health risks are less exciting from a media standpoint: the stress of travelling in economy class presents a far greater health risk than deep vein thromboses or microbial diseases. There is no question that sleep deprivation, standing in lines, undignified security, carrying heavy bags, and going hungry can take years off of one's life.