"The truth of the matter is, the engineering in the F-35 is appalling," Sprey said, adding that the attack jet's "main mission is to send money to Lockheed [Martin]."

When compared to the F-16, Sprey described the F-35 as slower, less maneuverable and more difficult to fly due to its "frightening" cockpit visibility for pilots. Sprey also challenged the plane's ultimate usefulness to national defense, charging that its long-delayed development — now the most expensive weapons system in U.S. history — is driven more by political reasons than by military ones.

On Tuesday, Sprey offered a room full of mostly F-35 opponents a blunt assessment of the new jet — and the politics of the generals pushing its development.

The 76-year-old Sprey speaks from experience. In 1967 he was brought to work at the Pentagon by then-defense secretary Robert McNamara. While there, he helped design the F-16 fighter jet, the A-10 "Warthog" ground attack jet, as well as tanks and anti-tank weapons. He left the Pentagon in 1971 but remained an active consultant on military systems through the late 1970s and has served as a defense analyst ever since.

Sprey also challenged claims by the Vermont Air National Guard that they'd be adequately prepared to deal with such an accident, noting that the video of a catastrophic crash and explosion of a B-2 bomber in 2008 "scared the pee out of every fire chief who looked at it."

Sprey further warned that an F-35 crash in or around Chittenden County would produce dangerous levels of highly toxic gases and fibers, due to the burning of all its plastic components and stealth coating materials. He suggested that such a crash would be "a catastrophe of major proportions" that could "potentially blanket blocks and blocks" of residential neighborhoods in deadly gases for days, likening the effects to a "chemical warfare attack" in Syria.

Sprey charged that it would be both "dangerous" and "irresponsible" for the Air Force to base these new and sophisticated jets in a highly populated area such as South Burlington before they've logged enough flight time to work out all the bugs.

Pierre Sprey, a defense analyst and co-designer of some of the military's toughest and most reliable warplanes, was in Burlington Tuesday warning of the potential dangers of basing the F-35 attack jets at Burlington International Airport.

Of concern to many of the people in attendance — Sprey's visit was sponsored by opponents of basing the F-35s at BTV — were the conclusions he outlined in a six-page report. Among his chief arguments:

1. All new fighters have high accident rates, he explained, which are higher than mature fighter planes and much higher than scheduled commerical airliners. And, because the F-35s are being produced so slowly — the Air Force is taking delivery on only 19 F-35As per year through 2017 — Sprey predicts the planes will not have more than 100,000 "fleet hours" before they're pressed into service at BTV.

2. Basing a new fighter with significantly less than 1 million fleet hours of safety experience in an urban area exposes Chittenden County residents to accident probabilities that he calls "irresponsibly high."

3. Sprey attacked the Vermont Air National Guard's estimate that the F-35A will have 750,000 cumulative fleet flight hours upon its arrival at BTV. According to his own calculations, he estimates that the F-35A is unlikely to have much more than 100,000 flight hours by 2020, which he called "grossly inadequate for judging its safety."

4. As a result, Sprey called the elevated accident risk that occurs between 100,000 flight hours and a million flight hours "substantial."

5. Since the F-35 is a new and far more sophisticated aircraft than either of its predecessors, the F-16 or the F-22, Sprey claims the Air Force cannot accurately gauge its potential accident rate. He notes that the F-22 has two engines, whereas the F-35 has just one. And, because the F-35 flight computer runs five times as many lines of computer code, Sprey says, "One may reasonably anticipate that the accident rate of the F-35 will be significantly higher than the F-22."

Much of the audience in Contois Auditorium seemed supportive of Sprey's conclusions. Although two F-16 pilots who serve with the Vermont Air National Guard were in the room to observe, they declined to comment on Sprey's assessments of the F-35 and said a statement would be issued later Tuesday from VTANG's public information officer. None had been released as of this posting.

The Rev. Peter Cook, senior pastor at the First Congregational Church in Burlington, who was among the two dozen spectators in the audience, said that one of his chief concerns is that there be a "balanced conversation" on this issue. He complained that each side in the F-35 debate keeps coming in with "wheelbarrows of facts" that "get dumped at the feet of the opposition and then they walk away." Cook said the lack of engagement between the two sides makes it very adifficult for the average citizen to weigh and interpret those facts and then decide which ones they find valid.

For his part, Sprey said he's happy to "sit down with a calculator and numbers" with anyone from VTANG or the Air Force who challenges his assessments. Sprey went on to critcize the statistical analyses provided by VTANG in its assessment of the F-35s' safety risk to the Burlington area, including one claim that the F-16 is safer than commercial airliners.

"That's so ludicrous I can hardly deal with it," Sprey said, calling the calculations in VTANG's spreadsheets "the most childish, kindergarten mistakes in statistics you can imagine. It's really a sad piece of work."

Sprey also leveled criticism at those who contend the F-16 is no longer a viable fighter jet. Noting that there are still DC-3s from the 1930s in the air today, he argued that the decision to permanently ground the F-16 "is a political decision, not a technical decision."

"There's zero truth to the statement that if you get rid of the F-16s, then the Vermont Air National Guard would be out of business," he charged, adding that if Sen. Patrick Leahy "put as much effort into keeping the F-16s as he has in getting rid of them, they could fly until 2050."