Investigation
The police quickly surrounded the site and removed any spectators; recovery of airplane pieces started soon. Both the cockpit voice recorder and flight data recorder were found quickly; unfortunately, the recording suddenly stopped nine seconds after the last transmission, 26 seconds before the crash.
While recovering the engines, the inner left engine - engine number 2 - was found to be cut in half, held together only by the fuel lines. When the engine was further examined, the disc of the low pressure turbine was found to be missing; despite extensive search, it was not found at the crash site. Finally, the turbine disc was found about four kilometres (2.5 miles) from the site; it was broken into three similar-sized pieces.
After recovering the cockpit, the throttles of both engine 2 and 3 (inner right) were found to be set to shutdown mode, while on engine 4 (outer right) the thrust was set to maximum. The investigating commission asked the Russians if Il-62 was able to reach the runway with one engine operating; no conclusive answer was received, but calculations based on the official technical data suggested that, while one engine thrust was insufficient for the aircraft to maintain altitude, it was enough to reach the runway and try to land. No explanation was found why the aircraft with one engine operating at maximum power suddenly entered a steep dive.
Detailed analysis of the pieces of the turbine disc found several metallic impurities on the edges of two of them; in one case, they were identified as coming from the engine nacelle, in another, the impurities came from the nacelle, the hull, the control pushers and finally, the electric wires. Also, detailed examination of the surface of the broken disc showed significant evidence of material fatigue.
Read more about this topic: LOT Flight 7