Over the past two weeks, several equipment outages at the Philadelphia-based air traffic control center that guides planes to and from Newark Liberty International Airport, have raised questions on just how safe it is to fly at one of the nation’s busiest airports.

United Airlines Chief Executive Scott Kirby told customers in an email Monday that it is “absolutely safe” to fly in and out of Newark Liberty International Airport following two weeks of technology and air-traffic control staffing issues that have plagued the New Jersey transit hub.

Technology and staffing problems have plagued the airport, one of the nation’s busiest hubs. Officials say they are trying to resolve the issues, but concerns remain.