Mumbai is a city synonymous with congestion. The 25-km. drive from its international airport to the city center can take up to three hours during the morning rush.  However, visitors to India’s financial capital often experience delays long before they even leave the airport. Airspace congestion means that flights can be left circling the city for up to an hour before receiving the necessary landing clearance.  This has earned the Chhatrapati Shivaji International Airport a spot on the unenviable list of world’s most-delayed airports. Yet, a seldom-discussed truth is that Mumbai’s flight delays would persist even in the absence of congestion. The reason? Air traffic controller shortages.

The Times of India reports staffing at the local air traffic control (ATC) center stands at 255, well short of the 455 controllers needed to do the job. This invariably leads to what amounts to traffic jams in the sky. Yet Mumbai’s predicament is hardly unique. According to the International Federation of Air Traffic Controllers’ Association (IFATCA), shortages in this niche profession are a global problem. They also come at a time when the number of commercial airplanes flying worldwide is expected to increase from 21,600 in 2014 to 43,560 in 2034. To manage all that extra metal, a series of recruitment and training campaigns have been launched to train more air traffic controllers. For example, early 2015 saw a purpose-built ATC training facility open in the Middle East. Capable of delivering instruction for up to 200 students annually, it boasts a state-of-the-art simulator that offers new recruits a highly realistic and immersive training experience. Similar initiatives are underway in Puerto Rico and China.

Such efforts are well intentioned. Training more controllers is one sure-fire means of alleviating airspace congestion. But it also comes at a cost.

Formal training programs provide instruction on the fundamentals of the job. New recruits learn how to separate different types of airplanes, what phraseology to use when talking to pilots and how to respond to distress calls. Yet perfecting these skills takes time. Writer Malcolm Gladwell famously opined such mastery could entail undergoing 10,000 hours of practice. In the lead up to perfection, mistakes will be made and for controllers, these mistakes can be costly. In fact, a recent study by the Université Paris Descartes found that controllers with fewer than six years on the job are disproportionately more likely to be involved in safety incidents compared to their more experienced counterparts. This conclusion was reached after analyzing over 7,000 incident reports filed in the United States. It also comes on the heels of a University of Illinois study that found similar effects in a more controlled laboratory setting.

A single controller erring due to inexperience is not the major concern. Technology can catch the one aircraft pair that get too close for comfort. Checklists can ease anxious nerves during an unexpected emergency. Most importantly, experienced controllers stand ready to step in and lend a helping hand. However, when large numbers of new recruits simultaneously enter the workforce, the delicate balance between experts and novices shifts. This increases the risk of errors. The increased risk is particularly problematic for the United States where nearly 10,000 new recruits are on track to be hired by 2019 to make up for a wave of retirements. According to the Transportation Department’s in-house watchdog, such a seismic demographic shift may explain why the number of controller errors has increased over the last few years.

Airspace congestion due to controller shortages is costly. The European Commission recently estimated that such inefficiencies cost airlines and their customers an extra €5 billion  annually. Adding new recruits can help address this problem. More bodies managing airplanes means those airplanes spend less time spent stuck in the sky. Yet sharpening the skills cannot be rushed. Until new recruits get up to speed, passengers may have to remain in their seats for a little longer than they planned. Rest assured, they will be safe at least.