Let L-410 crash at Rzhevka

The Let L-410 crash at Rzhevka was an aviation accident that occurred on Friday 3 August 1979 in the Kovalyovsky Forest near Rzhevka Airport in Leningrad Oblast involving an L-410M (Л-410М) aircraft of the Aeroflot enterprise, in which 10 people died.

Crash

The aircraft was operating flight 1643 from Smolensk to Leningrad. It was flown by a crew from the 287th Flight Detachment consisting of instructor pilot N. S. Levy, trainee captain V. A. Tsymbalov and co-pilot V. L. Maleyevsky. At 10:40 Moscow time the L-410 took off from Velikiye Luki, where it had made an intermediate stop. There were 11 passengers on board.

When approaching Rzhevka, the crew switched to communication with the airport controller, after which they began the approach to land on a magnetic heading of 237°. The weather at the airport at that time was as follows: cumulonimbus cloud 4 oktas, cloud base 800 metres, visibility 10 kilometres, wind 230° (south-westerly) 8 m/s, gusts up to 11 m/s. At 11:54 the aircraft made the fourth turn and entered the final approach, in connection with which the pilots reported readiness to land. The controller gave them this clearance. At 11:56 the controller noticed that the aircraft had stopped descending and was beginning to turn right. He then asked the pilots: «Are you going around?», to which they replied: «Yes, yes, we're going around». After that, communication with the aircraft ceased.

The L-410 was flying in landing configuration (landing gear down and flaps at 35°) at a speed of 165 km/h when, in the area of the inner marker (BPRM), its right engine suddenly failed and the propeller went into autorotation. The crew tried to feather the propeller with the propeller control lever (RUVV) of the right engine, but despite the lever being moved, feathering did not occur. The unfeathered right propeller created high aerodynamic drag, while the left one was operating in thrust mode. A yawing moment arose, which caused the aircraft to turn right away from the landing heading. Events developed quickly, as a result of which the crew was forced to go around, for which the left engine's power was set at a level close to take-off power. The pilots tried to counter the right yawing moment by deflecting the rudder to the left, but L-410 aircraft have relatively little rudder travel, so the aircraft continued to enter a right turn. This also led to a right bank, which quickly reached 30°, after which a stall onto the right wing occurred, further increasing the right bank.

At an angle of 30° and with a right bank of 25°, the airliner, flying on a heading of 305°, crashed into a pine forest 500 metres from the runway threshold and 550 metres to the right of its centreline. Having moved 12 metres along the ground from the point of first contact, the aircraft broke apart. No fire broke out. All three pilots and seven passengers died in the crash. The four surviving passengers suffered serious injuries.

Causes of the crash

According to the results of the investigation, the failure and self-shutdown of the right engine were caused by the destruction of the bearing assembly of the spring shaft of the engine's accessory gearbox. The flight time since the engine's last scheduled maintenance (every 100 flight hours) was 4 hours 49 minutes. As for the unfeathered position of the right propeller, according to the conclusion of GosNII GA (State Research Institute of Civil Aviation), the reason for this may have been the RUVV moving off the «feather» stop and moving by itself into a position at which the propeller could go to the minimum in-flight blade pitch angle — 15°. The RUVV moving off could have occurred due to a spring-back effect from the elastic play of the lever at the feather stop, which was confirmed by the position of the right engine's RUVV determined during the investigation — 8 millimetres beyond the BSh stop.

It was also noted that the flight operations manual (RLE) lacked recommendations:

for landing in the event of an engine failure on final approach with a windmilling propeller;

for landing in the event of an engine failure on final approach with a feathered propeller;

for going around in the event of an engine failure on final approach with a windmilling propeller.

Conclusion: The cause of the crash was the loss of controllability of the aircraft when the crew attempted to go around owing to the failure of the right power plant on final approach and the absence in the L-410M RLE of recommendations to the crew on actions in these conditions.