Experimental evidence showed that during manual landings pilots attempted to match a vertical speed / altitude profile given by a control law of the form:
Ht above runway = 3.3 x vertical speed – 12 ft.
There is a range of values for both the time constant (3.3) and the ht offset (12) that will still give a touchdown of 2 ft/sec.
The ref document RAE / BLEU ‘landings in fog’ showed two changes of landing profile with reduced visibility. First, an over-flare, which resulted in a ‘high’ float from which the aircraft quickly dropped onto the runway as airspeed reduced; some pilots tended to push over in theses conditions.
Secondly, a late flare by misjudging the flare ht. In this case:-
Either the flare was not corrected, resulting in a firm touchdown,
or with over rotation at an airspeed above the ideal, resulted in the float condition above.
or with a more extreme deviation (high VS at low alt) the crew over-rotated in an attempt to regain the flare profile (aiming for a 2ft/sec landing).
The latter condition increased the risk of a tail strike if the airspeed was lower than the ideal.
Therefore, the airspeed in addition to the visual cues available during flare (pilot perception) plays a major part in a landing. Poor judgement of height – late flare – over rotation may result a tail strike if the airspeed is low, but with ideal airspeed you may only get a firm touchdown. Thus airspeed appears to be a major parameter, especially the V^2 term for lift, and providing thrust can be applied quickly it may be the dominant effect in preventing a tail strike.
Also see the latest FSF Digest
Stabilized Approach and Flare Are Keys to Avoiding Hard Landings The document requires Acrobat reader Ver 6 (available from Adobe download).