CALGARY -- The Transportation Safety Board says there should be a better way of determining whether a train's brakes are working as they should.

The agency wrote to Transport Canada last month asking what it intends to do about shortcomings with the current method for testing air brakes.

The issue came up during the board's ongoing investigation into a Canadian Pacific train derailment near Field, B.C., which killed three railroaders last year.

The agency says that train passed the No. 1 brake test in Calgary before it set out on the fatal trip.

The No. 1 test is meant to verify that at least 95 per cent of a train's air brakes are operative, but does not physically measure their force or effect.

The safety board says research comparing brake testing methods, along with concerns flagged by Canadian Pacific employees before the Field derailment, suggest the No. 1 brake test is not reliable.

”Given this information, Transport Canada is advised that an alternate approach to determining the effectiveness of freight car air brakes is required to ensure that departing trains have sufficient effective brakes to operate safely,” the board wrote in its April 17 letter.

”The TSB would appreciate being advised of TC's position on this issue, and what action, if any, will be taken in this regard.”

The Vancouver-bound Canadian Pacific grain train was stopped on a mountain slope in the frigid early-morning hours of Feb. 4, 2019, when it began moving on its own, sped down a treacherous hill in Yoho National Park and plummeted from a bridge over the Kicking Horse River.

Conductor Dylan Paradis, engineer Andrew Dockrell and trainee Daniel Waldenberger-Bulmer died.

Ninety-nine of the train's 112 cars and two of its three locomotives derailed.

The train's previous crew had been unable to control its speed and brought it to an emergency stop before the crash, the safety board said.

The agency noted in its letter that Transport Canada, the National Research Council and Canadian Pacific began a research project in 2015 looking at an air-brake test called automated train brake effectiveness.

Researchers examined wheel temperature data from detectors at the bottom of big hills where prolonged applications of air brakes were needed to control train speed.

Early results in 2016 found a high frequency of grain cars with cold wheels were under-braking.

Researchers then compared that test with the No. 1 brake test on 44 grain trains. The testing being researched found 695 cars with ineffective brakes, whereas the No. 1 brake test only found five.

The board also said in its letter that it reviewed hazard notifications that Canadian Pacific employees had submitted to the company's health and safety committee before the fatal derailment.

It found several cases where train crews had difficulty controlling speed in cold weather while descending the same steep hill in the Rocky Mountains where the crash happened.

”These hazard notifications document air-brake performance issues on unit grain trains that had successfully passed a No. 1 brake test.”

Transportation Safety Board spokesman Alexandre Fournier said Transport Canada has not responded to the letter, and is not required by law to do so.

Transport Canada spokeswoman Frederica Dupuis said in a statement that the ministry is reviewing the letter.

”Rail safety is the top priority for the minister of transport and the department is continuously looking for ways to make our railway system safer for Canadians,” she said.

”We share the Transportation Safety Board of Canada's commitment to advancing the safety of Canada's transportation system and are committed to working with our partners to further enhance the safety of Canada's railway system.”

This report by The Canadian Press was first published May 12, 2020