Plane that crashed in Bangor has history of failing in icy weather

The plane that crashed at the Bangor airport Sunday night during a snowstorm has a history of failing during winter weather conditions — and was the subject of two federal directives to improve flight manual instructions for de-icing.

Six people are presumed dead, according to Bangor police, after the Bombardier Challenger 600 plane flipped over and caught fire as it was taking off around 7:45 p.m. The victims have not all been identified.

While investigators have not yet determined the cause of the crash, multiple aviation experts told the Bangor Daily News that possible ice or snow on the plane’s wings could have been a factor and that authorities will be on the lookout for information about the de-icing it underwent before attempting takeoff.

The model involved in Sunday’s crash, a Bombardier Challenger 600 jet, is known to be particularly vulnerable to ice and snow. The Challenger 600 series is a set of business jets manufactured by the Canadian company Bombardier that can carry up to two crew members and nine passengers.

Following two similar crashes in the early 2000s, the FAA issued a directive in 2005 for Challenger 600 operators to more carefully inspect wings for ice and frost before taking off, “prompted by a report that even small amounts of frost, ice, snow or slush on the wing leading edges or forward upper wing surfaces can cause an adverse change.”

The FAA released another directive in 2022 for multiple Bombardier models, including the one involved in Sunday’s crash, prompted by reports of wing stall during landing. The ruling required revisions to the plane’s flight manual regarding the wing anti-ice system “in order to mitigate the risk of ice accumulation on the wing leading edges.”

Bombardier did not respond to a request for comment.

It’s not yet clear what caused the crash in Bangor. It may have been caused by engine failure or mechanical failure, according to Foundation for Aviation Safety advisory board member Randy Klatt, but it’s also possible weather conditions were the cause. Klatt is a former U.S. Navy pilot and aviation safety officer.

This plane is “pretty well known in the circles of those who fly it” to be more sensitive to ice and winter weather conditions, Klatt said. Its aerodynamic design makes the plane’s wings “a little more sensitive to ice build-up,” he added.

“It’s something that you really have to be very careful of in that particular airplane and others that are similar in design,” Klatt said.

It’s very important to make sure wings are completely free of ice and snow, Klatt added.

“The wing has to be pretty darn smooth,” he said.

There are two processes to keep the wings clean: type one de-icing, which removes snow that has accumulated while the plane is on the ground, and type four, a “viscous” fluid applied to the wing that prevents snow from accumulating, according to Klatt.

There are many factors, including temperatures, precipitation, visibility and the brand of de-icing fluid used, that can affect the holdover time, or the amount of time the anti-ice treatment is effective, Klatt said.

Air traffic control recordings indicate that the Challenger’s crew underwent both type one and type four de-icing treatments Sunday night. Someone who is presumably the pilot told controllers he was heading over to get de-iced around 7:08 p.m., and he arrived and requested de-icing treatments around 7:17 p.m. Around 7:35 p.m., he announced that the plane was “ready to taxi,” and he was cleared for takeoff around 7:42 p.m.

The time between de-icing and takeoff — approximately 25 minutes or more — could have exceeded the holdover time depending on the type of fluid used, according to Klatt.

If there was residual snow or ice, or if the crew pushed the limit of the holdover time and more snow or ice built up on one of the wings, that could explain why one side of the plane lifted more than the other and it rolled over upside down, he said, although that rolling over could also have been caused by engine failure. Since the plane was headed to France, it also would have been particularly heavy because it would have had a lot of fuel on board, he added.

Around the same time the Challenger plane was being de-iced, an Allegiant Airlines pilot turned back to the gate because of weather conditions, air traffic control recordings reveal.

“One, our de-ice fluid just failed, and two, I don’t think the visibility is good enough for us to go. So we’re going to have to taxi back to the gate here,” the pilot said.

Federal investigators are starting to arrive in Bangor on Tuesday, two days after the crash. The agency’s response has been delayed by the snowstorm.

Investigators will likely examine weather conditions and the plane’s maintenance history, according to John Cox, a former executive air safety chairman for the Air Line Pilots Association International who has trained aviation accident investigators.

“What we don’t know is if the airplane had ice on it when it took off,” he said. “There’s some period of time between the end of de-icing and the beginning of takeoff roll — how long was that period of time, and what kind of deicing fluid was used in the deicing process?”

Cox said he knows of two other crashes of this type of plane where there was a ground icing issue.

A Challenger 601 plane crashed and caught fire, in similar fashion to what happened Sunday in Bangor, while taking off from Montrose, Colorado, in 2004. Three people died and three others were seriously injured.

The National Transportation Safety Board later determined failure to remove ice and snow from the plane’s wings as the cause of the crash. Investigators also noted the pilots’ lack of experience flying in winter weather conditions as a factor.

A law firm that filed suit over the 2004 crash argued that the plane’s airfoil was “dangerously too sensitive to ice contamination” and the manufacturer had failed to adequately warn flight crews operating the plane in winter conditions.

In 2002, a Challenger 604 plane rolled uncontrollably to the side and caught on fire during takeoff en route to Bangor from Birmingham, United Kingdom. A British investigation found that the pilots did not de-ice the plane and attributed the crash to frost on the wing.

After the 2005 FAA directive, the manufacturer said it would change flight manuals to instruct pilots to run their hands along the plane’s wings to inspect for ice instead of just looking at them, the Washington Post reported.

The plane has also had issues after failure to turn on its wing anti-icing system after getting a de-icing treatment on the ground. In 2007, a Challenger 604 plane crashed and caught fire shortly after takeoff from Almaty, Kazakhstan. One crew member died.

An Interstate Aviation Committee investigation concluded that although the crew completed a de-icing treatment, they probably lost control of the plane because they failed to turn on the wing anti-ice system and more snow accumulated on the wing.