Originally Posted by
silverstrata
With the SW 3472 incident in 2016, plus the SW 438 incident in 2007, and now this, I think the focus of attention needs to be as much on the cowl as the blade. In two (perhaps all three) cases the root of an N1 fan-blade failed (due to fatigue on the 2016 incident) and the blade separated.
But in all three cases the blade appears to have missed the containment ring and struck the cowl instead, causing a complete failure of the cowl, and all the attendant risks with all that material flying off into the slipstream. If you look at the N1 containment ring on the recent incident, it appears to be untouched all the way around. But the cowl took the full force of the departing blade, and disintegrated.
The N1 blade is under considerable aerodynamic forward pressure in flight, and will naturally spring forwards when released. But in static testing for cerification the blade still seems to hit the containment ring. Yet here it appears that the blade moved forward enough to miss the containment ring, and strike the cowl. Perhaps an engineer on this board might suggest why that might be. Why would the forward speed of the aircraft have any effect on the trajectory of the departing blade?
ST
Just for general understanding .. the released blade loses significant aero forces such as lift as soon as it is released. Given that it now contacts the engine casing within milliseconds the forces acting on the blade tip are friction against tangential inertia. Like a downhill skier the blade tip follows the line of lowest friction which skate it forward of the plane of rotation.
I was struck by the excellent quality of the referenced NTSB Walk-around video and the observation that the engine itself closely matched the manufacturer's successfully certified blade out test.
The secondary events immediately following the loss of the blade now become of primary importance to resolve.