Federal officials are investigating the collision of an Air Canada regional jet with a fire truck on a runway at LaGuardia Airport in Queens late Sunday. Both pilots were killed and dozens were injured in the crash, which led to days of delays at one of the country’s key regional hubs.

Officials from the National Transportation Safety Board said the preliminary investigation suggests the accident was caused by an overlapping series of failures that stemmed from problems with staffing and technology.

Here’s what we know:

The Investigation

The plane, a CRJ900 operating as Air Canada Express Flight 8646, had flown from Montreal with 72 passengers and four crew members aboard, according to its operator Jazz Aviation, a regional carrier in Canada.

The fire truck, a Port Authority Aircraft Rescue and Firefighting vehicle, crossed onto the runway where the jet was landing at around 11:40 p.m. on Sunday, officials said. It had been responding to a separate incident involving a United Airlines flight that had aborted its departure because of a foul odor onboard.

In recordings of air traffic control audio communications, a person in the fire truck requests and receives permission to cross a runway, before an air traffic control operator tells the vehicle to stop. “Stop, Truck 1, stop!” the controller can be heard saying.

After the collision, the controller can be heard telling the pilot of another plane, “I messed up.”

On Tuesday, Jennifer Homendy, the N.T.S.B. chairwoman, said there were two people in the tower, the local controller and the controller in charge. But investigators did not yet have a clear sense of how many controllers were on duty at the time of the crash.

The Federal Aviation Administration said staffing levels at the LaGuardia control tower would be part of the investigation.

Investigators do not know if the two occupants of the fire truck heard the air traffic controller’s commands to stop, which began roughly nine seconds before the impact. Ms. Homendy also said that the fire truck lacked a transponder, making it difficult for the airport’s early-warning systems to track its position.

“When something goes wrong,” Ms. Homendy said, “it means many, many things went wrong.”

The Timeline of the Crash

Several minutes before the crash, investigators said, air traffic controllers were responding to an emergency with United Airlines Flight 2384, which had aborted a takeoff attempt at 10:40 p.m. The pilots made a second attempt at takeoff about 40 minutes later and aborted again.

At 11:31 p.m., the United flight, citing an odor that had sickened members of the flight crew, declared an emergency and requested a gate assignment, according to air traffic control audio reviewed by The New York Times.

Air Canada Express Flight 8646 was set to land at LaGuardia when the approach controller, who manages flights as they near the airport, ordered the airplane to contact the control tower, N.T.S.B. officials said.

The Air Canada flight crew began lowering the landing gear. The plane was cleared to land on Runway 4 and advised that it was No. 2 for landing, Doug Brazy, a senior aviation accident investigator with the N.T.S.B., said.

Around 11:37 p.m., or 25 seconds before the crash, the fire truck, which was responding to the emergency with the United plane, made a request to cross Runway 4 at Taxiway D, the same runway that the Air Canada jet was set to land on.

The Air Canada jet was about 100 feet above the ground when the air traffic controller gave permission for the truck to cross the runway.

Eleven seconds later, a controller yelled over the radio at the truck’s driver to stop immediately, Mr. Brazy said.

One second after that, the plane touched down, he said. Three seconds later, the captain assumed control of the plane from the first officer. The jet rolled on the runway for another seven seconds, braking hard.

Then the plane struck the fire truck. The nose of the plane imploded and the fire truck flipped on its side, spraying debris across the tarmac

Who were the victims?

The pilots were identified on Tuesday as Antoine Forest, 30, and Mackenzie Gunther. The New York City Office of Chief Medical Examiner determined that they died from blunt-force injuries.

Forty-one victims were taken to the hospital after the crash, said Kathryn Garcia, the executive director of the Port Authority of New York and New Jersey, which operates the airport. Six people remained hospitalized as of late Tuesday, Air Canada said in a statement.

The officers in the truck, whom the Port Authority identified as Sgt. Michael Orsillo and Officer Adrian Baez, were injured. Officer Baez was released from a hospital on Monday night and Sergeant Orsillo remained hospitalized on Tuesday.

How will this affect air travel?

The runway where the crash occurred remained closed as the N.T.S.B. conducted its investigation. Travelers continued to face significant disruptions as flights were restricted primarily to a single runway. A federal notice said the runway could reopen on Friday.

The disruptions added to travel strife at U.S. airports caused by the partial government shutdown.

One of three major airports in the New York City area, LaGuardia is a hub for travel in the Northeast, with nearly 900 arrivals and departures per day.