Wendy Tadros issued a statement on Saturday saying the TSB stands by its findings that faulty electrical wiring caused a fire aboard Swissair Flight 111.
The statement came a day after the CBC aired a documentary containing claims by a retired Mountie who was part of the investigation.
Tom Juby alleges that TSB investigators failed to fully explore whether an incendiary device may have brought down the plane.
The crash off the Nova Scotia coast killed 229 people.
Tadros said she has "every faith" in the probe, adding the victims' families took some solace from the thorough job done by investigators.
"We are dismayed that this irresponsible speculation will only reopen old wounds," she said in the statement.
"This investigation has really contributed to making air transportation safer."
Juby based his claim on the fact that high levels of magnesium — a key ingredient in an incendiary device — were discovered in the cockpit area.
He said he was prevented from pursuing his suspicions and that the TSB had prematurely concluded the crash was an accident.
Larry Vance, who was the TSB's deputy investigator in the Swissair investigation, said on Friday that his team traced the fire to a single wire that showed signs of electrical arcing, a phenomenon in which electricity flashes like lightning, vaporizing everything in its path.
An incendiary device would have caused more damage and arcing in many of the other wires in the area, Vance said.