Northern airline First Air cancelled six flights Wednesday because of ash from Alaska's Pavlof Volcano, which erupted Sunday afternoon with little warning.
The company also cancelled 14 flights Tuesday due to the cloud of ash that's moving east across northern Canada.
"The aircraft would actually be flying in a cloud of very small rocks that act like sandpaper on an aircraft," said First Air's vice president, Bert van der Stege.
"It can do substantial damage, such as heavily scratching the windows and eroding all forward facing surfaces, like wings and propellers."
Van der Stege said ash clouds can also seriously damage an aircraft's engine, even causing it to fail — but he says not all aircraft are affected equally.
"Like any regular cloud, an ash cloud can be avoided by flying above, below or around it," said Van der Stege.
"But the forecasts for the cloud indicated that the clouds could begin at the surface, so flying under it wasn't an option, and the forecast indicated that it was extending as high as 34,000 feet, which is actually higher than our propeller aircraft is allowed to fly."
According to Van der Stege, a Boeing 737 can fly at that altitude, but usually does so only on longer legs.
Van der Stege says 550 customers have been affected, but the company is not expecting any further delays.
Calm Air cancelled all of its flights in and out of Rankin Inlet, Nunavut, on Wednesday.
Ashy plume heading east
Environment Canada says the ashy plume is currently east of Yellowknife, spanning through Nunavut's Kivalliq region and down through northern and central Manitoba.
"As the flow is continuing to push it down to Manitoba a lot of the small particles will fall out," said Kirk Torneby, a meteorologist with Environment Canada.
"The actual threat of volcanic ash will be decreasing over the next 12 to 24 hours."
Canadian North says its flights have not been affected.
Kelly Lewis, spokesperson for Canadian North, says the airline is paying close attention to Environment Canada reports on the location and concentration of the ash cloud, and that its pilots and maintenance staff have been actively looking for signs of ash in the air and on aircraft.
"The presence of ash on the routes that we're operating is negligible," said Lewis.
He added that the airline is still cautioning passengers that its flights could be affected if conditions change.
Mount Pavlof is one of the most active volcanoes on the Alaska peninsula. Its eruption on Sunday prompted flight cancellations across North America.
The U.S. Geological Survey said in a news release late Monday night that the intensity of the eruption from Pavlof had "declined significantly."