Originally Posted by
WideScreen
A headwind, reducing close to the ground, will let you drop out of the air due to insufficient airspeed, whereas a tailwind, reducing close to the ground, will increase the airspeed and as such, keeps you flying/floating longer, IE your landing spot automatically moves further down the runway.
The dynamics of a shear associated with the turbulent boundary layer is quite straightforward, but the aiming point is the aiming point, and the flare/ thrust reduction is a process that is trained and mastered by the pilot in qualification. A rollout will be extended by the higher ground speed, nut nothing in Part 25 Subpart B lets the pilot off the hook for not being able to fly a path to an aiming point, flare/reduce power at an appropriate time and land.
In simple terms an into wind landing has an undershoot shear where the wind component reduces due to the TBL approaching the ground. Response is a pitch adjustment and thrust change while transiting the shear to maintain parameters. The immediate change is a reduction in IAS from inertial factors, while groundspeed increases... speed stability results in the attitude naturally lowering which matches the higher sink rate rest for the higher ground speed. Once sterilised conditions occur, thrust and pitch change to maintain the higher sink condition for a geometric glide path.
For the tailwind case, indeed the handling is more fun; the reducing tailwind in the TBL gives an inertial effect of an increase in IAS, which gives arose up moment from speed (alpha) stability), the GS reduces so the required VS for the geometric path then requires IAS to be stabilised, thrust initially comes off but then has to be set at slightly higher levels than that required prior to the shear.... and the stable conditions attained. It is an overshoot shear, and is one of the reasons that for high inertia aircraft like the 747/777/380 etc reference ground speed or GSmini was a nice briefing item, it gets a target in mind as to what is going to be the processes for the maintenance of a stable path.
The requirement is still to maintain a path, and to arrive at the flare point with the correct energy state, so my query stands. Are we saying that pilot training is inadequate to fly an aircraft within normal criteria for a stable approach?
In respect to this bingle, the LH MLG has impacted soft ground prior to the lip of the runway hard surface, which is commonly called landing short. If the premise is that in order to not land long on a landing with a tailwind, instead we ens up with landing short, effectively having a ramp strike, then we seem to have other problems. As a simple horizontal shear to cause an outcome like that in a closed loop control system would be an instantaneous loss of the 0.3 amount of the 1.3Vs that Is being applied on the reference speed, or a sudden/instantaneous loss of 25kts of tailwind component. That being the reason to have some inkling of GSmini (lé Busse), RGS (Billie Boing) etc... For low inertia aircraft, the effects are less pronounced, but mechanical turbulence can be more annoying.
Still, Fokker made a solid tube, plane handled that bingle rather well.