Increased stress on the engines and lengthening of the service interval led to growth failure. There were cases when the IL-62 flew from the United States to Warsaw without passengers, on three engines. Representatives of the technical staff at the John F. Kennedy Airport reported two similar flights in the past two years. The most common causes of failure were bending or breaking of the blades. Consequently, there weren't enough serviceable engines. LOT fell into the practice of using three engines within the service interval, and a fourth beyond the interval. The investigation revealed the practice to be widespread. The airline called the fourth engines "leaders".