The disadvantage is as usual - extra complexity and weight.
Not as much weight and complexity as this:
787 Controls
Maybe IF SS feedback/interconnection was available it would not have happened.
But
IF ADR2 hadn't have been the voted median.....
IF they hadn't switch over to ADR3 (display on RH PFD)...
IF captain had returned to cockpit earlier (or never left)....
IF PF didn't overreact......
IF multiple UAS had lasted longer than 10s in the first fase....
IF they had realized what was going on....
IF training,knowledge, CRM, communication, SOPs would have been sufficient.....
IF AoA indicator was fitted (or BUSS was opted)....
IF inertials had been outside the abnormal attitude values.....
The outcome could have been different too!
Maybe the clues are in the modifications which have been adopted after this tragedy.
For systems:
- Inhibition of AP/FD reconnect after UAS.
- More rigid USE MAN PITCH TRIM PFD msg when autotrim is not available.
- F/CTL ALT LAW (PROT LOST) msg accompanied with reason what caused the transition.
IMO the installation of an AoA indicator will be mandated - in the final report - because it is already optional and provisions are available.