French investigators are recommending extension of minimum retention terms for maintenance documents after a serious in-flight propeller-blade separation badly damaged a Fokker F-27 freighter.
Investigation authority BEA says a fatigue fracture caused the blade to break, and shear off a second blade which passed completely through the aircraft's fuselage.
But BEA says it "could not determine with certainty" the cause of the fracture on the MiniLiner aircraft, which had been operating out of Paris Charles de Gaulle for Europe Airpost on 25 October 2013.
The inquiry says the number two blade on the left-hand Rolls-Royce Dart 532-7 engine separated following a failure of its root anchor bolt, and struck the number one blade.
Loss of the two blades created an "imbalance" which sheared off a forward section of the engine, it adds.
But the number one blade also sliced through the fuselage vertically, passing through the freighter's hold and exiting on the right-hand side of the fuselage.
It says tests on the blade root showed that the microstructure and composition were "not optimal" in terms of fatigue resistance, but points out that the aircraft is an old design and that the component was probably manufactured in the 1960s.
Maintenance documents covering overhaul of the propeller in June 2009 had been destroyed in July 2012, in line with European regulations which only stipulate a three-year preservation term.
Measurements such as pre-loading of bearings, as a result, could not be recovered. But the maintenance facility indicated that detailed inspection of the anchor bolts had not detected any cracks.
BEA is recommending that the European Aviation Safety Agency modifies its Part-145 maintenance requirements to ensure that operators or engineering facilities maintain detailed records long enough to reduce the risk of useful information being lost, or until such data is superseded.
Previous recommendations advising that EASA should require retention of maintenance records until components are permanently removed from service have met with resistance. BEA says EASA considered such a measure amounted to "more paper, preserved for a long time, without a safety benefit".
Source: Cirium Dashboard
