Two World War II-era military aircraft collided mid-air and crashed at Dallas Executive Airport during an air show Saturday afternoon, killing all aboard.   

  More than 40 fire and rescue units responded to the scene after the two vintage planes – a Boeing B-17 Flying Fortress and a Bell P-63 Kingcobra – crashed during the Wings Over Dallas air show.   

  In video footage of the crash, which Dallas’ mayor described as “heartbreaking,” the planes can be seen disintegrating in midair after impact, then hitting the ground within seconds before bursting into flames.   

  Here are the latest developments as investigators from the National Transportation Safety Board are set to arrive at the scene Sunday.   

  The Federal Aviation Administration said the crash happened around 1:20 a.m. Saturday.  The number of victims has not yet been confirmed, according to Dallas Mayor Eric Johnson on Saturday.   

  The Allied Pilots Association – the labor union representing American Airlines pilots – identified two retired pilots and former union members among those killed in the crash.   

  Former members Terry Barker and Len Root crewed the B-17 Flying Fortress during the air show, APA said on social media.   

  “Our hearts go out to their families, friends and colleagues past and present,” the union said.  APA is offering professional counseling services at its Fort Worth headquarters following the incident.   

  At a press conference Saturday, Hank Coates, president and CEO of the Commemorative Air Force, an organization that maintains and preserves vintage military aircraft, told reporters that the B-17 “typically has a crew of four to five people.  That was on the aircraft,” while the P-63 is a “single-pilot fighter-type aircraft.”   

  “I can tell you it was normally manned,” Coates said.  “I cannot release the number of people on the manifest or the names on the manifest until I am released by the NTSB.”   

  The Commemorative Air Force identified both aircraft as being based in Houston.   

  “We currently have no information on the condition of the flight crews as emergency responders work the accident,” the group said in a statement, adding that it was working with local authorities and the FAA.   

  No injuries to spectators or others on the ground were reported, although the debris field from the crash includes the grounds of Dallas Executive Airport, the 67 Freeway and a nearby shopping center.   

  The B-17 was part of the Air Force Memorial collection, nicknamed the “Texas Raiders,” and was kept in a hanger in Conroe, Texas, near Houston.   

  It was one of approximately 45 complete surviving examples of the model, only nine of which were seaworthy.   

  The P-63 was even rarer.  About 14 examples are known to survive, four of which in the US were airworthy, including one owned by the Commemorative Air Force.   

  More than 12,000 B-17s were produced by Boeing, Douglas Aircraft and Lockheed between 1936 and 1945, with nearly 5,000 lost during the war and most of the rest scrapped in the early 1960s. About 3,300 P -63 were manufactured by Bell Aircraft between 1943 and 1945 and were used primarily by the Soviet Air Force in World War II.   

  The FAA led the investigation into the air show crash on Saturday, but it was to be handed over to the NTSB once its team arrived at the scene, Coates said.   

  On Saturday night, the NTSB said it was sending a team to investigate the crash.  The team, which is made up of technical experts regularly dispatched to plane crash sites, is expected to arrive on Sunday, the agency said.   

  According to Coates, the people who fly the aircraft at CAF air shows are volunteers and go through a rigorous training process.  Many of them are airline pilots, retired airline pilots or retired military pilots.   

  “The maneuvers that (the aircraft) were going through were not dynamic at all,” Coates noted.  “It was what we call ‘parade bombers.’   

  “It’s not about the aircraft.  It just isn’t,” Coates said.  “I can tell you that the aircraft are excellent aircraft, they are safe.  They are very well preserved.  The pilots are very well trained.  So it’s hard for me to talk about it because I know all these people, they’re family and they’re good friends.”   

  Mayor Johnson tweeted after the crash: “As many of you have now seen, we had a terrible tragedy in our city today during an air show.  Many details remain unknown or unconfirmed at this time.”   

  “The videos are heartbreaking.  Please say a prayer for the souls who ascended to heaven to entertain and educate our families today,” Johnson said in a separate tweet.   

  The Wings Over Dallas event, which was scheduled to run through Sunday, has been canceled, according to the promoter’s website.