With regard to "sudden" and "sharp" turns: -
(i) a lot of you will have seen military jet displays at airshows and may recollect what it looks like when the commentators say "this is a 7G turn". It is difficult to assess both the radius of the curve and, more importantly, the aircraft's speed just by looking at them but aerobatic displays are, typically, confined to an imaginary "box", which only rarely strays outside the aerodrome's boundaries, on the ground. For the sake of argument, let's call the curve about 1km in diameter (or 500m radius). The speed remains unknown but, probably, is *not* 400 knots.
(ii) Civil aircraft speed limit, below 10,000 feet is 250 knots. The bulk of earth's atmosphere is below this altitude and flying too fast here wastes fuel and risks overstressing the aircraft, during maneuvres. But the speed limit is more to do with safety, ease of air traffic control, reducing noise disturbance and other factors.
(iii) Ground speed (GS), Indicated Airspeed (IAS) and True Airspeed (TAS) are three different things. Flightradar24 is giving me readings of 500knots and upwards, for airliners in high altitude cruise but the pilots will be more interested in the indicated airspeed as that relates closer to aerofoil performance and structural stress. The wing 'feels' an airflow equivalent to 400+ knots. This is roughly 205 metres/sec.
Using the centripetal force formula F=m.v^2/r with
m=65000(kg) (derived from Wiki stats for Airbus A320-200)
v=205 m/s
r= various values (in metres) eg 1000, 500 as the radius
a=F/m so I divide by 65000 again, to get an acceleration, divide again, by 9.81 to get a readout in g.
((65000*(205^2)/1000)/65000)/9.81 = 4.28g
((65000*(205^2)/500)/65000)/9.81 = 8.567g
News reports describe these turns being visible on the flight-tracker website. We don't know what map scale they were viewing the replay on but a zoom level showing both Crete and Egypt on the map would reduce a turn radius of 500m to a mere speck. We need more information before we can draw anything from this part of the account.
The broad point that I'm making is that, at cruising speed, a turn radius of 1000 metres would subject you to over 4g's and many of us, of a certain age or health condition would black out.
Known only to Airbus Industrie is the g-loading which will break the wings or tail surfaces off. Famously, the aircraft is "fly-by-wire" and, additionally, the flight computer will not allow the joystick to apply foolish or potentially damaging inputs to the aircraft control surfaces. One would have to smash extensive parts of the cockpit to remove this computerised oversight.
The Germanwings flight did entail some deliberate - and inappropriate - autopilot input. Sadly Aircraft do not contain a database of world mountain ranges with which to cross-check that a requested altitude would be safe, although I see no reason why software couldn't take care of this. Anyway, inputs via the autopilot would have resulted in smooth maneuvres, no untoward g-forces and would have gone largely unnoticed.