Miniliner F27 at Paris on Oct 25th 2013, left propeller separated in flight
Last Update: February 12, 2018 / 16:18:54 GMT/Zulu time
French Gendarmerie du Transport Aerien (GTA) reported that the propeller was found in a field near Le Mesnil-Amelot just east of the northern runways of Charles de Gaulle Airport on Oct 26th 2013, the front section of the engine still attached.
On Oct 26th 2013 the airline confirmed I-MLVT on flight to Dole was involved in the accident.
On Oct 27th 2013 the French BEA reported, that a few minutes after takeoff at 01:10L (23:10Z Oct 24th) the aircraft suffered "a failure not contained in the left hand engine", a left hand propeller blade passed through the fuselage. The aircraft landed safely at 01:20L. Three investigators were dispatched on site to collect evidence into the occurrence rated an accident.
Late Nov 8th 2013 the BEA released additional information stating, that first results of examination of the propeller blade identified a fatigue failure of the screw. When a blade subsequently passed through the fuselage it severed a number of power cables supplying the black boxes causing that there are no data following the event available from the recorders.
On Apr 30th 2014 Italy's ANSV reported in their annual report 2013, that one of the left hand propeller's blades detached from the propeller and engine assembly crossing through the fuselage. This resulted in an imbalance of the propeller assembly which caused the propeller assembly to separate from the engine. The crew verified controllability of the aircraft, declared emergency and returned to Charles de Gaulle Airport. The propeller assembly was later found in a farm field with 3 of the 4 propeller blades still attached. The BEA is leading the investigation into the occurrence rated an accident.
A French "Aviation News Service" reported the aircraft involved was I-MLRT doing flight 5O-5807 from Paris Charles de Gaulle to Clermont-Ferrand (France). If this was true, the crippled aircraft would have continued the flight to Clermont-Ferrand and departed for its onward flight 5O-5677 from Clermont Ferrand to Limoges (France) with just one propeller and a large hole in its fuselage. In the meantime that "service" have corrected their coverage.
On Feb 12th 2018 the French BEA released their final report in French only concluding the probable causes were:
fatigue fracture at the blade root
A screw at the root of propeller blade #2 of the left hand engine fractured as result of fatigue, which caused the blade to liberate from the propeller hub. Blade #2 contacted blade #1 causing that blade to separate from the hub, too. The liberation of two propeller blades caused an imbalance which tore down the front section of the engine.
The investigtion could not determine with certainty what caused the fracture.
The following may have contributed to the fracture:
- incorrect torque on the screw increasing the forces attacking on the screw. The lack of maintenance documentation did not permit to determine the torque used during last mainenance.
- presence of Mangan-Sulfur in a zone of high stress within the screw. The presence of Sulphur may have served as a stress concentration factor increasing the level of local stress. Tests and research carried out by the investigation suggest that the blades consisted of steel the micro-structure and composition of which were not optimal with respect to resistance against fatigue. However, the uniqueness of the occurrence after the propellers were put into service more than 50 years ago makes it unlikely that the inclusions, their distribution, their size of content of sulphur contributed to the fracture.
Preservation of maintenance documentation
During the investigation it was not possible to determine the maintenance actions taken during last overhaul of the propeller, the maintenance documents had been destroyed. The destruction of the documentation by the workshop was in accordance with EASA regulative, which requires maintenance documents to be kept for three years after the end of the mainenance work (ICAO Annex 6 requires only one year). This issue had been noticed by the AAIB during another investigation already, a safety recommendation was released to EASA at that time.
Due to the extreme technicality of the French text (analysis, report of laboratory research) and AVH limitations in translation capability no further summary of the report will be provided (unless the BEA decides to release an English version, too).
This article is published under license from Avherald.com. © of text by Avherald.com.
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