The Federal Court of Appeal says six legal challenges to the Trans Mountain pipeline project focusing on Indigenous consultation can proceed.

The federal government has twice approved a plan to triple the capacity of an existing pipeline from Alberta's oilpatch to a terminal in Burnaby, B.C.

Last year the Federal Court of Appeal tore up the original approval, citing both an insufficient environmental review and inadequate consultations with Indigenous communities.

The Liberals say they fixed both problems and approved the expansion a second time in June.

Environmental groups and First Nations sought leave to appeal, arguing the ecological assessment and consultation process were deficient the second time as well.

The court has released a written decision saying it will allow six of the 12 requests to appeal.

It says the allowed challenges are limited to the narrow issue of the adequacy of the consultation with Indigenous Peoples and related issues between Aug. 30, 2018, the date of the court's earlier decision, and June 18, 2019, when the government approved the project a second time.

The court has ordered that the challenges proceed on an expedited basis. It says short and strict deadlines for the steps in the litigation will be set.

Environment groups still say there are not adequate protections for endangered marine species that will be affected by tanker traffic picking up oil from the terminal in suburban Vancouver.

Several First Nations say the federal government came into the most recent discussions having predetermined the outcome.

The federal government bought the existing pipeline and the unfinished expansion work for $4.5 billion last year, promising to get it over the political opposition that had scared off Kinder Morgan Canada from proceeding.

The move disappointed environmentalists, who say the global climate can't handle more emissions from Alberta's oilsands and the eventual burning of the petroleum they produce. The Liberals say they'll use any profits from the project to fund Canada's transition to a cleaner-energy economy.