This is bunk: the passenger's contract is with Air Canada and the legal obligation to comply with accessibility legislation is on Air Canada. Subcontracting does not absolve AC of responsibility regardless how many indemnification clauses their overly-clever lawyers have inserted into the contracting arrangements. I would love to see them try to take up this line of argument with the DOT.

Furthermore, Air Canada failed to take all reasonable steps to mitigate the harm caused by the 3rd party's failure by standing and watching the pax crawl off the plane instead of doing literally anything to remedy the situation.

It's really disgusting that an airline employee would see a disabled person in agony with half a dozen airline employees looking on and conclude that the real problem is people don't understand that the wheelchairs are provided by a different company.