The evasive action an airline pilot took to avoid a B-52 bomber in the skies over North Dakota has focused attention on the way small airport towers are often run by private companies without their own radars.

Neither one of the pilots of the bomber or of the Delta Air Lines jet seemed to know the other plane was there before the airline pilot saw the B-52 looming in its path. The incident last Friday is still under investigation. But the Air Force has said the controller at the Minot airport didn’t let the bomber’s crew know about the airliner, and the SkyWest pilot flying the Delta flight told passengers he was surprised.

Passengers were alarmed by the sharp turn and dive the pilot of Delta Flight 3788 executed to avoid the bomber that had just completed a flyover at the State Fair in Minot, and a video shot aboard the plane captured the pilot’s explanation afterward.

“Sorry about the aggressive maneuver. It caught me by surprise,” the pilot can be heard saying on the video posted on social media. “This is not normal at all. I don’t know why they didn’t give us a heads-up.”

This close call is just the latest incident to raise questions about aviation safety in the wake of January’s midair collision over Washington, D.C., that killed 67 people. Here’s more about the way small airports like Minot operate:

Many small airports lack radar

It is common for small airports across the country to operate without their own radar systems because it would be too costly to install them at every airport. But there generally aren’t many problems with that.

The controllers at small airports are able to guide planes in to land visually with binoculars and radios as long as the weather is clear. Aviation safety consultant Jeff Guzzetti, who used to investigate crashes for both the National Transportation Safety Board and Federal Aviation Administration, said if the weather is bad, a regional FAA radar facility may be able to help, but ultimately planes simply won’t land if the weather is too bad.

Sometimes small airport towers do have a video feed that gives controllers a view of a radar screen at an FAA facility miles away. Because the radar is so far away the display may not be as detailed about planes flying close to the ground, but the system does give controllers more information. It’s not clear if the Minot tower has one of those systems because the company that runs it, Midwest Air Traffic Control Inc., hasn’t responded to questions since the incident.

The overlapping network of FAA radar facilities across the country also keeps track of planes flying between airports, and an approach control radar center in Minneapolis helps direct planes in and out of Minot before controllers at the airport take over once they see the planes. The Minot airport typically handles between 18 and 24 flights a day. That’s how it works at many small airports.

“Most times it works just fine,” Guzzetti said.

Some of these small airports could gain radar as part of a massive overhaul of the air traffic control system, but that will depend on how busy the airports are and how much funding Congress ultimately approves for the multibillion-dollar project. So far, $12.5 billion was included in President Trump’s overall budget bill.

Private companies

operate the towers

The FAA says that 265 airport towers nationwide are operated by companies as part of the contract system. The Transportation Department’s Inspector General has said the contract towers that handle more than one quarter of the nation’s flights are more cost effective than comparable FAA towers and have similar safety records. In some cases, local governments help pay the costs of contract towers.

The program began in 1982 at five less busy towers that had closed because of the air traffic controller strike the previous year, and it has expanded significantly over the years because it has been so successful. Most of the airports with contract towers would have no controllers without the program.

“Common sense would tell you that having an extra set of eyes controlling the local traffic — especially in good weather — would be safer than having no controller and just having the pilots talking to each other,” Guzzetti said.

That’s exactly how it works at the vast majority of the 5,100 public airports nationwide that are smaller than Minot. Pilots at those uncontrolled airports use their radios to coordinate takeoffs and landings with other planes in the area. Only about 10% of all airports have towers.

The FAA says it works closely with the companies that run contract towers to ensure their controllers are properly trained. It is easier to get certified at a contract tower because they handle fewer flights than FAA towers even though controllers are held to the same standard.