"Keith W" wrote in message
news
Jim Wilkins wrote:
At 2h 12m ~15s the Pilot Flying made a pitch-down input that
brought
their forward speed above the stall warning's lower limit of 60 Kts
and it sounded again, confusing them.
Page 44 of the final report:
" If the CAS measurements for
the three ADR are lower than 60 kt, the angle of attack values of
the
three ADR are
invalid and the stall warning is then inoperative."
My real point is to remind Bill Black that he lives in a glass
house
and shouldn't throw stones at Boeing.
jsw
The real point is that the aircraft clearly
1) Indicated that it had reverted to direct law (manual input)
2) Sounded the stall warning
3) Showed that the aircraft was falling at a high angle of attack
and low speed
The pilot flying seems to have been fixated on keeping the
wings level and disregarded the angle of attack which at
2 minutes 12 seconds was 40 degrees ! During the entire
crisis it was never less than 35 degrees.
Keith
"When the calculation of the Vsw speed is not available, this speed is
no longer
displayed on the PFDs. No visual information is then displayed that is
specific to the
approach to stall."
"The angle of attack is the parameter that allows the stall warning to
be triggered. Its
value is not directly displayed to the pilots."
They knew their small nose-up angle, but not the large relative wind
direction component of AoA.
Speculation based on similar non-fatal incidents:
"The reappearance of the flight directors on the PFD when two
airspeeds are calculated
as similar may prompt the crew to promptly engage an autopilot.
However, although
the magnitude of these speeds may be the same, they may be erroneous
and low,
and could cause the autopilot to command flight control surface
movements that are
incompatible with the aircraft's actual speed.
They dance around the possibility that the Flight Director crossbars
on the Primary Flight Display might have misled the crew. The PFD is
on page 39. The reconstructon of information available to the crew
begins on p.93.
jsw