"FAA says it's unsafe and, in a classic kind of FAA schizophrenia, they don't do anything about it," says Mary Schiavo, former inspector general for the U.S. Department of Transportation. It's a position that made her the watchdog over the FAA.
At the center of the concerns: insulation on Boeing aircraft produced in the 1980s. Insulation blankets completely wrap the hull of an airliner. They're supposed to protect passengers.
Block says, "They are all around the aircraft to muffle noise, to keep heat in and air conditioning in."
"a small ignition source, such as an electrical arc, could easily ignite this material and the fire would propagate on the material until the material was consumed. Flames from the AN-26 were capable of igniting other aircraft materials and, in a cascading fashion, cause a catastrophic fire."
Add to that: a highly explosive type of wiring, called Kapton, found on some of the very same aircraft.
"It's like gasoline on a fire," says Block, a former Department of Defense wiring specialist. "The ignition point you're getting from a Kapton arc tracking plus the flammability of the ignition blanket there's no question that it's going to ignite it."
In fact, our investigation discovered safety reports filed by the airlines regarding "burn spots" on insulation from numerous aircraft, "fire in the insulation blankets," even an "insulation blanket badly burned."
And the FAA videos show how those flames could spread from one insulation blanket to another.
"What's amazing to me is that it goes out in all directions," says former Northwest Airlines pilot Don McCune.
And as the flames spread, so does the toxic cloud of smoke. The videos show how smoky it would become where the passengers sit.
"It can take you 20 minutes to get down," Schiavo says. "The pilots and flight attendants have smoke hoods, the passengers don't."
Block adds, "When they drop the air bags for you to breathe through, that's mixing with cabin air. So you're breathing in that smoke."
As a result, Schiavo notes, "You could be in a situation even if you can get the plane down your passengers would be dead."
In fact, crash investigators discovered it was just that type of fire that sent SwissAir 111 crashing into the Atlantic 10 years ago.
The video shows why the FAA ordered the removal of another flammable insulation -- called metallized Mylar -- from hundreds of older McDonnell-Douglas aircraft.
But for some reason, the insulation on the Boeing aircraft escaped the FAA's attention.
Three years later, the FAA said it was going to require other airlines to do the same.
"Removing the insulation from an aircraft is like removing the second layer of skin on a human body," McCune says. "It's a big undertaking and it's very expensive."
That's why, despite the images, McCune says the airline industry has now been negotiating with the FAA for three years to let it come up with a different plan.
In the meantime, nothing has happened.
"These aircraft that have this are getting older, and I think the airlines are hoping that they get parked before the insulation has to be replaced," he explains.
It's a situation, these advocates argue, not unlike the controversy over how the FAA let Southwest Airlines keep flying without the required safety inspections.
"They know about a problem but they resist acting," Schiavo says. "Unfortunately, they resist acting because, well, to put it into their words, they don't have a body count."
So every day, hundreds of those airliners take flight with flammable insulation -- and what the FAA says is an "unsafe condition."
"This is an accident looking for a place to happen," Block says.
The FAA issued the following statement:
"As shown by the number of ADs [airworthiness directives] issued to eliminate ignition sources, other rules issued to require enhancements to wiring design and maintenance practices, as well as the thermal/acoustic insulation blanket final rules, it is clear the FAA takes smoke and fire issues very seriously.
"Due to the scope and estimated cost of the AN-26 proposed rule, we received a significant number of comments. We are required to evaluate every comment received on the proposed rule. At this time, we have completed the evaluations and are in the process of finalizing the proposed rule."
Despite the agency's dire warnings, there's been no official action in the rulemaking process for almost a year.