TAIC says Te Huia train separation caused by faulty link between carraiges

The back two carriages of the Te Huia train were left about 500 metres down the track from the rest of the train after breaking away just 10 minutes into the journey. Photo / Kiley O'Meara

An Auckland to Hamilton train that came apart while carrying passengers mid-last year did so because a locking mechanism linking two carriages was shaken undone by repeated vibrations, investigators say.

The Transport Accident Investigation Commission today released its report into the incident on July 19 last year in which the back two carriages became detached from the rest of the Te Huia train about 10 minutes after leaving Auckland’s Papakura station.

The train’s emergency brakes fired immediately after the train came apart between its second and third carriages, with the carriages coming to a halt about 500m behind the front of the train.

No one was injured and the transport crew reconnected the carriages and continued on slowly, allowing passengers to get off at the next station at Pukekohe.

The train then continued to Hamilton, however it once again separated between the same two carriages.

TAIC’s chief investigator of accidents Naveen Kozhuppakalam said KiwiRail and its supplier company had improved their testing procedures for the linkages between carriages as a result of the incident.

However, Kozhuppakalam recommended KiwiRail staff be better trained in how to handle incidents where carriages separate because staff failed to disengage the carriages’ emergency brakes after reconnecting the separated carriages.

It was the fact the emergency brakes were still on that led the carriages to separate a second time, he said.

Although the incident caused no injuries, investigators said it not only frightened passengers but created a real danger a passenger or crew member could have fallen from the train.

The Te Huia passenger train service between Hamilton and Auckland launched in April 2021. Photo / Supplied

It also raised safety concerns over the then-newly launched Te Huia Auckland-Hamilton train service.

Waikato woman Kiley O’Meara was in the first of the two back carriages that separated from the rest of the train just 10 minutes after it left Papakura station at 4.42pm that day.

The train had just travelled across a level crossing when she heard “a god awful noise” as the emergency brakes kicked in and the carriages ground to a halt about 500m away from the rest of the train.

“There was just this open door and we were just looking and the train and the entrance were down the tracks,” she said at the time.

She said the screeching brakes made a really loud “steel on steel sound”, almost like the train had hit a vehicle.

TAIC ’s Kozhuppakalam said the brakes were triggered immediately for both the train and the separated carriages because the “braking system air hoses between the carriages also separated”.

He said investigators concluded the link between the carriages knowns as a coupler came apart because of vibrations.

“It is virtually certain the knuckle of the newly fitted coupler at the rear of the second carriage opened because vibration caused its lock to creep out of position,” he said.

The Te Huia train service. Photo / Danielle Zollickhofer

This fault was not detected by quality checks by the manufacturer of the coupler, Amsted, Kozhuppakalam said.

Testing to see if this fault existed was also not a part of KiwiRail’s commissioning process when these couplers were fixed onto the Te Huia train’s carriages.

However, Amsted and KiwiRail had now worked together to “resolve this issue, so there was no need for TAIC to recommend a solution”, Kozhuppakalam said.

After the carriages first separated, he said the train crew rejoined “the parted train portions and the train continued slowly to the next station (Pukekohe), where passengers disembarked”.

“It is virtually certain that the train made this 7.5km journey with the park brakes on the front two carriages engaged all the way.”

“Mechanical staff examined the train and it continued without passengers toward Hamilton, limited to 55km/h, and then it parted again between the same two carriages.”

Kozhuppakalam said the first two carriages’ park brakes remained locked on because of an electrical disruption caused by the train’s separation.

“After recoupling, the train driver pressed a button to release the park brakes and moved off,” he said.

“But the brakes remained engaged because their control circuits had been disrupted when the cables between the carriages broke. The train dragged its brakes all the way to Pukekohe Station.”

Having the brakes locked on “very likely” caused “flat spots” on the train’s wheels that in turn caused more vibrations that again caused the link between the carriages to shake open.

“It is virtually certain the knuckle of the newly fitted coupler at the rear of the second carriage opened because vibration caused its lock to creep out of position,” Kozhuppakalam said.

The separation made a "god awful" sound of "steel on steel" a passenger said at the time. Photo / Kiley O'Meara

He said KiwiRail staff needed to be better trained in such circumstances to check that all brakes are disengaged.

“KiwiRail did not control for the risk that its passenger carriages are vulnerable to trainline control circuits being disrupted after a train parting, due to inter-carriage jumper cables being severed and conductors being exposed,” he said.

“In this case, exposed wires shorted out, preventing release of the brake.

“Compounding this issue, KiwiRail’s procedures for recoupling a parted train did not require crew to check brake response (in this case, the train manager checked brake response only for the fourth carriage).”

Kozhuppakalam said TAIC recommended KiwiRail provide “guidance to staff responding to severance of inter-carriage jumper cables during the parting of passenger trains. KiwiRail has agreed and committed to develop a check sheet for train staff.”

The incident caused damage to the train and led KiwiRail to apologise to its passengers.