At the risk of stating the obvious, is it not the case that the horizontal tail on this a/c is way too small, no doubt in order to save fuel.
Isn't that behind all these landing accidents?
Hi Shy Talk.
The stab of the MD11 is just fine. The stabilizer is smaller than the one on DC10, but remember the MD11 has a longer fuselage (about 11 meters if I remember correct). And all that nonsense about dynamic instability is not true either. This is usually confused with that the cruise cg is aft during cruise, and has nothing to do with instability, although it true that margins are reduced, but well within designed flight envelope.
MD11 drivers have to know what they are flying, since the design creates some points that require attention. MD11 wing has one of the highest wing loading index of civil aircraft, and this creates the need for a higher approach speed. Higher app speed gives higher decent in ft/min. When flying near Vref during approach, if the speed is allowed to decrease slightly the sink rate increases quickly. This will result in a high sink rate upon landing. A natural reaction from the pilot is to pull the yoke to arrest the sink rate. Since the main landing gear is aft of the pivot point of the aircraft, if pulling the yoke below 15-10ft, the result is that the main gear is accelerated down into the ground with an already high sink rate = kabummm!!!!
After the first landing, because the pilot is trying to arrest the flare by pulling the yoke, the pitch attitude is high, and the aircraft bounces into flight again. At this stage the MD11 is still in one peace.
The next thing is that the pilot tries to pitch down, but since the aircraft have now gone well below Vref, the stabilizer is running out of efficiency and the natural effect is that the nose pitches down as well.
Then the pilot tries to counter act this by pulling again on the yoke, and then we are back to what happen in the first place with the main gear aft of the pivot point, high sink rate, high wing loading, high rate of decent. At this stage the MD11 will impact the runway with some 2,5-3 G. Then it bounces again and the last impact will give some 4G, well beyond any civil aircraft design limits.
All this have nothing to do with design flaws or what ever people think.
The recovery is just to ad thrust to arrest the sink rate. If this happens after Bitching Betty starts to count down, then a go around must be executed.
So MD11 requires different technique. If this is not understood the MD11 is not forgiving like say the 747. Nothing to do with design flaws.
Best regards
An ex MD11 driver