By DAVID KOENIG (AP Airlines Writer)

DALLAS (AP) — It has been 15 years since the last fatal crash of a U.S. airliner, but you would never know that by reading about a torrent of flight problems in the last three months.

There was a time when things like cracked windshields and minor engine problems didn’t turn up very often in the news.

That changed in January, when a panel plugging the space reserved for an unused emergency door blew off an Alaska Airlines jetliner 16,000 feet above Oregon. Pilots landed the Boeing 737 Max safely, but in the United States, media coverage of the flight quickly overshadowed a deadly runway crash in Tokyo three days earlier.

And concern about air safety — especially with Boeing planes — has not let up.

By the simplest measurement, the answer is no. The last deadly crash involving a U.S. airliner occurred in February 2009, an unprecedented streak of safety. There were 9.6 million flights last year.

The lack of fatal crashes does not fully capture the state of safety, however. In the past 15 months, a spate of close calls caught the attention of regulators and travelers.

Another measure is the number of times pilots broadcast an emergency call to air traffic controllers. Flightradar24, a popular tracking site, just compiled the numbers. The site’s data show such calls rising since mid-January but remaining below levels seen during much of 2023.

Emergency calls also are an imperfect gauge: the plane might not have been in immediate danger, and sometimes planes in trouble never alert controllers.

The National Safety Council estimates that Americans have a 1-in-93 chance of dying in a motor-vehicle crash, while deaths on airplanes are too rare to calculate the odds. Figures from the U.S. Department of Transportation tell a similar story.

“This is the safest form of transportation ever created, whereas every day on the nation’s roads about a 737 full of people dies,” Richard Aboulafia, a longtime aerospace analyst and consultant, said. The safety council estimates that more than 44,000 people died in U.S. vehicle crashes in 2023.

A panel of experts reported in November that a shortage of air traffic controllers, outdated plane-tracking technology and other problems presented a growing threat to safety in the sky.

“The current erosion in the margin of safety in the (national airspace system) caused by the confluence of these challenges is rendering the current level of safety unsustainable,” the group said in a 52-page report.

Many but not all of the recent incidents have involved Boeing planes.

Boeing is a $78 billion company, a leading U.S. exporter and a century-old, iconic name in aircraft manufacturing. It is one-half of the duopoly, along with Europe’s Airbus, that dominates the production of large passenger jets.

The company’s reputation, however, was greatly damaged by the crashes of two 737 Max jets — one in Indonesia in 2018, the other in Ethiopia the following year — that killed 346 people. Boeing has lost nearly $24 billion in the last five years. It has struggled with manufacturing flaws that at times delayed deliveries of 737s and long-haul 787 Dreamliners.

Boeing finally was beginning to regain its stride until the Alaska Airlines Max blowout. Investigators have focused on bolts that help secure the door-plug panel, but which were missing after a repair job at the Boeing factory.

The FBI is notifying passengers about a criminal investigation. The Federal Aviation Administration is stepping up oversight of the company.

“What is going on with the production at Boeing? There have been issues in the past. They don’t seem to be getting resolved,” FAA Administrator Mike Whitaker said last month.

CEO David Calhoun says no matter what conclusions investigators reach about the Alaska Airlines blowout, “Boeing is accountable for what happened” on the Alaska plane. “We caused the problem and we understand that.”

Problems attributed to an airplane manufacturer can differ greatly.

Some are design errors. On the original Boeing Max, the failure of a single sensor caused a flight-control system to point the nose of the plane down with great force — that happened before the deadly 2018 and 2019 Max crashes. It is a maxim in aviation that the failure of a single part should never be enough to bring down a plane.

In other cases, such as the door-plug panel that flew off the Alaska Airlines jet, it appears a mistake was made on the factory floor.

“Anything that results in death is worse, but design is a lot harder to deal with because you have to locate the problem and fix it,” said Aboulafia, the aerospace analyst. “In the manufacturing process, the fix is incredibly easy – don’t do” whatever caused the flaw in the first place.

Manufacturing quality appears to be an issue in other incidents too.

Earlier this month, the FAA proposed ordering airlines to inspect wiring bundles around the spoilers on Max jets. The order was prompted by a report that chafing of electrical wires due to faulty installation caused an airliner to roll 30 degrees in less than a second on a 2021 flight.

Even little things matter. After a LATAM Airlines Boeing 787 flying from Australia to New Zealand this month went into a nosedive — it recovered — Boeing reminded airlines to inspect switches to motors that move pilot seats. Published reports said a flight attendant accidentally hitting the switch likely caused the plunge.

Investigations into some incidents point to likely lapses in maintenance, and many close calls are due to errors by pilots or air traffic controllers.

This week, investigators disclosed that an American Airlines jet that overshot a runway in Texas had undergone a brake-replacement job four days earlier, and some hydraulic lines to the brakes were not properly reattached.

Earlier this month, a tire fell off a United Airlines Boeing 777 leaving San Francisco, and an American Airlines 777 made an emergency landing in Los Angeles with a flat tire.

A piece of the aluminum skin was discovered missing when a United Boeing 737 landed in Oregon last week. Unlike the brand-new Alaska jet that suffered the panel blowout, the United plane was 26 years old. Maintenance is up to the airline.

When a FedEx cargo plane landing last year in Austin, Texas, flew close over the top of a departing Southwest Airlines jet, it turned out that an air traffic controller had cleared both planes to use the same runway.

Aviation-industry officials say the most concerning events involve issues with flight controls, engines and structural integrity.

Other things such as cracked windshields and planes clipping each other at the airport rarely pose a safety threat. Warnings lights might indicate a serious problem or a false alarm.

“We take every event seriously,” former NTSB member John Goglia said, citing such vigilance as a contributor to the current crash-free streak. “The challenge we have in aviation is trying to keep it there.”