LOT Flight 5055 - Cause

Cause

After the crash of the Il-62 SP-LAA on LOT Polish Airlines Flight 007, LOT Polish Airlines started replacing their Ilyushin Il-62s with the more modernized version, Ilyushin Il-62Ms. These had newer engines (Soloviev D-30 instead of Kuznetsov NK-8), but both of these turbofan engines shared the same critical point — low pressure turbine and engine shaft design and construction.

According to the Polish investigatory commission, the cause of the crash was the disintegration of an engine shaft due to faulty bearings inside the number 2 engine, which seized, causing extensive heat. This in turn caused the consequent damage to engine number 1 (and its fire), rapid decompression of the hull, a fire in the cargo hold (which was not detected due to a damaged fire alarm system sensor), as well as the loss of elevator controls and progressive electrical failure.

The bearings concerned were roller bearings; each was designed to have 26 rollers inside, but because the supply of the rollers to the factory was delayed — while the bearings had to be finished on time due to expiring contracts — each bearing had only 13 rollers.