What happened
On April 17, 2014, an Embraer 175, registration SP-LIO, operated by PLL LOT S.A., was climbing through the air when the crew noticed the left engine's internal turbine temperature (ITT) reaching the maximum allowable limit of approximately 900°C. To manage the temperature, the captain adjusted the FMC mode from CLIMB1 to CLIMB2 and reduced the flight level from FL 390 to FL 370, which successfully lowered the ITT to about 880°C.
As the aircraft reached FL 370 and transitioned to cruise mode, the crew began accelerating to cruise speed. At approximately Mach 0.73, a loud noise, described as an explosion, was heard throughout the cabin. While the crew initially suspected the cargo hold, they continued the flight. Upon receiving instructions from Russian Air Traffic Control to increase speed to Mach 0.78, a second similar loud noise occurred. The crew subsequently reduced speed, citing suspected engine malfunction, and proceeded to land without further incident. Following the landing, technical teams at Pulkovo Airport (ULLI) determined that the number 1 engine required replacement.
The investigation
The investigation focused on determining the origin of the loud noises and the mechanical state of the engine. Investigators examined the engine's internal components and reviewed the operational parameters recorded during the climb and cruise phases. The investigation also reviewed the airline's maintenance and software update protocols for the Embraer fleet.
Findings
- The primary cause of the incident was contact between the rotor blades and the high-pressure compressor stator blades.
- This contact was triggered by material fatigue in a stator element.
- The incident occurred while the engine was operating at high thermal parameters during the climb phase.