What happened
On 26 November 2016, a Boeing 787-9, registration 9V-OJF, operated by Scoot, departed Sydney for Singapore. During the initial climb, the flight crew observed vibration levels in the Low Pressure (LP) section of the No. 2 engine reaching 3.8 units. While vibration levels fluctuated during the cruise phase, they remained within operational limits, prompting the crew to continue the flight while monitoring the engine parameters.
As the aircraft descended toward Singapore Changi Airport, a loud bang was heard, followed by the automatic shutdown of the No. 2 engine. The crew received an engine damage alert on the cockpit displays and declared an emergency. Although passengers reported seeing what appeared to be fire from the engine, the crew confirmed no external fire was visible. The aircraft landed safely at 1842 hrs with no injuries to the 351 people on board.
The investigation
Post-flight inspections of the No. 2 engine revealed significant internal damage, including a missing first-stage Intermediate Pressure (IP) compressor blade and a missing variable inlet guide vane. Metal debris was found scattered within the engine, and several fan blades showed impact damage. Detailed workshop analysis discovered that seven other blades in the first-stage IP compressor had cracks approximately 30.5mm in size at the blade root.
Investigators also examined the engine's internal environment, finding evidence of a titanium fire within the engine core and damage consistent with a compressor surge. The investigation also reviewed air traffic control procedures, noting that a takeoff clearance was granted to another aircraft when the emergency flight was only 5.5NM from touchdown, contrary to the standard practice of reserving the runway for emergency arrivals within 20NM.
Findings
- The primary cause of the engine failure was material fatigue leading to cracks at the roots of the first-stage IP compressor blades.
- The loss of a single blade triggered a sequence of mechanical damage and a compressor surge.
- The cracks likely originated from fatigue, though the exact initiation mechanism remains under investigation by the manufacturer.
- The engine experienced internal fire damage due to the combustion of titanium components during the failure event.
- The vibration noted during the climb was likely caused by the rubbing of blade roots within their slots, known as galling.