I have been thinking on similar lines to Safetypee’s post 2839.
There have been a number of references in this thread to the QRH procedures for flight with unreliable airspeed. Some of the comments seem to imply this is an easy task- just set the power, maintain the pitch attitude and it will work out. I am not convinced.
This procedure may be fine in stable weather situations, but all the evidence suggests AF447 was encountering far from benign conditions.
Let us assume that around the major Cbs in the ITCZ there were significant horizontal and vertical windshears, a not implausible scenario. An encounter with a rapidly increasing headwind would result in a rise in airspeed, which would need to be countered by a reduction in thrust to avoid a potential overspeed, but the crew would have no means of identifying this need and the speed rise would go unchecked..
.
If the crew were attempting to use GPS or inertial groundspeed as their cue (because there was no alternative) they would likely increase thrust instead of reducing it . Hence the risk of an overspeed would be greatly increased.
Now run the converse scenario of an increasing tailwind. Airspeed falls, crew unaware ,so do not take corrective action, ground speed increases, so thrust is reduced, result is underspeed.
Add in a further possibility. If at the instant of A/THR disconnect, the system had already reduced or added thrust to counteract a speed excursion, crew action to set the QRH reference power could actually exacerbate the speed error.
In the vast majority of situations, one would expect these effects to be minor, transient and hence containable. Is it possible that in the weather situation in which AF447 found itself, the effects were major and cumulative, to the extent that a critical underspeed or overspeed
occurred ?
Even if this situation did not take place, it seems to me the crew had a major task on their hands that could have reduced their capacity to manage any other.event that might have occurred. It may not be necessary to speculate on the implications of Airbus Alternate Law -
the potential could be the same for all types. And I keep asking myself how well I would have coped.