The YF-22/F-22 is an unstable design in order to achieve maximum agility, it is stabilized via computer, (this is the case with many "fly by wire"
aircraft). The plane in question apparently had unanticipated aerodynamic characteristics in the low altitude, low speed regime.
In this particular case the resulting characteristic which brought the plane down hard was obviously "PIO", (Pilot Induced Oscilation) as already
suggested in some of the posts above. This PIO was most likely brought on by non-synchronous input from pilot and computer clashing with the
airframe's difficult aerodynamic form.
A software fix was probably needed to correct this problem.
I believe a company called
Barron Associates in Charlottesville, VA is addressing such
software issues with both manned and unmanned aerospace vehicles under a DARPA\USAF program called
"
Tactile Cueing for PIO Avoidance".
Problems are expected with most prototype aircraft - that's why test pilots get paid well.
Intelgurl
[edit on 22-9-2004 by intelgurl]