A Bombardier C Series CS100 (now known as an Airbus A220-100) was to be used for several engine ground runs (Pratt & Whitney Canada model PW1524G engines) during the test program for aircraft certification. The aircraft was located at the Montreal Internation (Mirabel) Airport. 6 people would be on board during the test, two test pilots, and 4 test engineers. While a trailer with support and servicing equipment was parked nearby. Seven additional engineers (from both Bombardier and Pratt & Withney) were on-site to assist, one of them was using the aircraft interphone system to communicate with the flight crew.
The engine after the uncontained failure of the Low-pressure turbine (© TSB Canada)
Two tests were scheduled;
During an engine ground run of the righthand engine, samples of the cabin air would be taken with the engine at different thrust settings
During an engine ground run of the lefthand, also at different thrust settings, a leak check would be carried out of an oil pump assembly. This pump had been replaced as part of a troubleshooting process because of an oil consumption issue. This test would be carried out in two steps; First, the engine would be run with the thrust reverser doors open, and a second run would be performed with the thrust reverser doors closed and secured.
The first test was started after all necessary checklists were completed the righthand engine was started at 15.14 lt (local time) and all required tests were completed by 17.00 lt.
Purple droplet showing oil leak in cooling (left) Flames showing area of explosion (right) (Source & © TSB Canada)
At 17.23 lt the left engine was dry motored for 1 minute and 38 seconds. (the engine is rotated using the starter motor, no fuel is introduced to the engine and ignition is disabled) After which maintenance staff carried out an inspection of the oil pump assembly for leaks, but no leaks were found.
Another start of the left engine was carried and the engine was left at idle for nearly eight minutes, for an additional leak check of the oil pump assembly, again no leaks were found
At 18.07 the left engine was started again and operated at different power levels. At 18.14 the engine power level was set to 60% N1 (the low-pressure spool of the engine), it remained at that thrust setting for a little more than 15 minutes. the engine power level was then increased to 74% N1, where it stabilized at 18.32 lt. 5 minutes and 45 seconds later an explosion occurred in the left engine, which started to immediately spool down.
The failed low-pressure turbine (Source & © TSB Canada)
Hearing the explosion ground staff immediately ran to the fire extinguishers, while the engineer in contact with the cockpit relayed his observations to the test pilots, one of them being there was a fire over the left-wing. In the cockpit, the crew received several alerts, but no engine fire warning;
L ENG FIRE DET FAIL
FIRE SYSTEM FAULT
When informed by the ground crew there was a fire on the wing the commander secured the left engine and shut down the right engine. while the co-pilot alerted the fire brigade.
The right front emergency exit was opened and all occupants safely evacuated the aircraft using the escape slide. In the meantime, the ground staff managed to extinguish the fire using the two-wheeled fire extinguishers from the service tailer. At 18,45 the fire brigade dispensed fire fighting foam on the aircraft, and 5 minutes later reported that the fire was extinguished.
PW1500 Series series engine, cutaway view (Source and © Pratt & Whitney)
The left engine had suffered an uncontained engine failure in the low-pressure turbine's first stage area. This caused substantial damage to the aircraft;
Wing lower surface
Landing gear doors
Fuel inerting equipement
The incident was investigated by the Transport Safety Board of Canada. They issued their final report in 2016, this report is available by clicking here.
Due to a combination of factors, an air oil mixture merged in the turbine cooling system, when temperatures in this system reached the autoignition point of the mixture, the explosion occurred and the low-pressure turbine rotor was ejected from the engine.