CRJ 200 / Wind shear warning - why follow F/D not "Eye brows"?
I`m an aviation enthusiast - and I have a question regarding "Wind shear alerts" and the corresponding G/A after such a warning.
Our company OM-A says we shall follow the F/D guidance. However, if the G/A button is hit - the "eye brows" on the PFD appear. Why wouldn`t I target the "eye brows" to get out of the situation asap - with max AoA and TOGA thrust I will get a bigger "safety cushion" underneath way faster than by following the F/D pitch... Can anyone explain? Did I catch something wrong? Thks!:ok: |
don't know if crj's eyebrows are special... but afaik the eyebrows indicate "PULL (over) HERE AND EAT IT"
so in a W/S situation with rapidly changing winds and airspeeds you might find yourself one step beyond the edge... |
Perhaps the aircraft has windshear recovery guidance in the FD system- (TOGA Windshear). If so then the FD should always be followed.
Most recovery control laws will consider the aircraft’s altitude and speed (total energy), and then compute a compromise FD command between not loosing altitude and minimising the time in the location. However, in a severe micoburst, the system’s optimisation would (should) direct a climb at the ‘eyebrow’ attitude thus minimise the likelihood of ground contact. |
Originally Posted by safetypee
(Post 5029545)
Perhaps the aircraft has windshear recovery guidance in the FD system- (TOGA Windshear).
Originally Posted by safetypee
(Post 5029545)
If so then the FD should always be followed.
Originally Posted by safetypee
(Post 5029545)
Most recovery control laws will consider the aircraft’s altitude and speed (total energy), and then compute a compromise FD command between not loosing altitude and minimising the time in the location. However, in a severe micoburst, the system’s optimisation would (should) direct a climb at the ‘eyebrow’ attitude thus minimise the likelihood of ground contact.
Originally Posted by D-IITC
Why wouldn`t I target the "eye brows" to get out of the situation asap - with max AoA and TOGA thrust I will get a bigger "safety cushion" underneath way faster than by following the F/D pitch...
As you get closer to the ground (assuming you're in a performance limiting WS and cant escape easily) the guidance will gradually eat into your margin to shaker, eventually commanding the FD coincident with the eyebrows at ground contact (thus fulfilling a basic certification requirement for WS guidance, that no "excess energy" be left unused at ground contact). But until you get to that point the margin above shaker represents both a "last ditch" energy reserve and also keeps your energy gain/loss rate as favourable as possible. Incidentally, although I heartily do not recommend this, the best escape manoeuvre for the certification windshear cases can often be a very close encounter with the ground - the downdraft inevitably tends to zero at the ground plane. of course, for cert purposes it IS a plane, and such inconveniences as houses, power lines and trees are generally absent.... |
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