OTTAWA -- The plane that flew Prime Minister Justin Trudeau to NATO — a replacement to begin with — has engine troubles and another aircraft has been sent to London to bring the delegation back.

According to the Prime Minister’s Office, the CC-150 Polaris plane “became unserviceable” after it arrived in London because a problem with one of the engines was discovered during a post-flight inspection by the Royal Canadian Air Force.  

A different CC-150 Polaris from the fleet has been sent to bring the delegation back to Canada later today. This backup to the backup was in Italy with Gov. Gen. Julie Payette for her visit to commemorate the Italian campaign during the Second World War and it has been diverted to transport the prime minister.

Despite this, the PMO says that Payette will still be home in time to read the throne speech happening in Ottawa tomorrow to open the new Parliament.

Trudeau and the group that travelled with him to the summit on Monday made the trek there on another replacement plane because the prime minister’s main plane had been grounded until August 2020, after a collision at CFB Trenton left it with a crushed nose and engine damage in October.

According to the Canadian Armed Forces, the main plane — a CC-150 Polaris used to transport the prime minister to international events — was being towed at the military airbase in Trenton, Ont. on Oct. 18 when it sustained “significant structural damage.”

The cost to repair the aging main plane, and now to fix the backup, remain unknown.

“In the meantime, the RCAF has other aircraft that can be used for transport and are confident it can meet the needs of the government while the aircraft is being repaired,” reads the statement from the PMO.

Plane troubles also dogged the Liberals during the fall federal election campaign. On the day Trudeau kicked off the election the Air Transat plane chartered by the Liberal Party was taken out of commission when a bus carrying the travelling media drove under and scraped up a wing.

A replacement was found, but then later on in the race Trudeau was criticized for using two planes during the campaign, one for the leader, his entourage and the media, and another for cargo.

As The Canadian Press has reported, during his first term the main prime minister’s plane also experienced problems. His arrival in India in 2018 was delayed due to a mechanical problem during a refuelling stop, and an incident with a flap required the jet to turn around shortly after taking off with Trudeau on board in 2016.

The Department of National Defence is projecting to spend up to $249 million to extend the lifespan of the fleet beyond 2026, according to documents. There’s been some discussion about whether now is the time to look into buying replacements.

Once dubbed "the flying Taj Mahal" by then-opposition leader Jean Chretien, the Airbus Polaris fleet is antiquated compared to most modern commercial aircraft, though it does have a private room for the prime minister to sleep in.

Flight crews on the main prime minister's plane run extension cords and power bars down the aisles to allow passengers to run their laptop computers.

With files from CTV News Senior Political Correspondent Glen McGregor