Re: NTSB recommend FAA to require installation of AOA system in all transport category aircraft

Date:         24 Oct 97 04:33:15 
From:         Michael W McGovern <mgovern@netcomuk.co.uk>
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Terry Schell wrote:
> s_odle@earthlink.net writes:
> <snip>
> >Why, is it any easier to fly angle of attack instead of airspeed?
>
> Because the important AOA's (best glide, stall, etc) do not vary with
> gross weight.   Finding best glide using airspeed requires knowing
> your weight at that time and then using a table/computer. Stall is
> even worse because you are very concerned about the effect of turns on
> stall speed. You need to know actual gross weight and then compute the
> force in the turn and *then* look it up in a table to find the stall
> speed.  With an AOA meter you just *look* at it; it will tell you
> exactly how much lift you can extract before a stall.  Any error in
> calculating your weight at that moment will result in blowing both
> computations when flying by airspeed.
>
> <snip>
> >Also, will the increase in level of safety (if there is any) be enough
> >to offset the cost of implementing such a system in all aircraft?
>
> The cost? Let's see...  one piece of yarn attached to the outside of a
> window, a grease pencil mark on the inside for best L/D, another mark
> for stall. (Just kidding there... I am just sure that the AOA gauge
> will need to be electronic, triple-redundant, and integrated into the
> FMC.)

I think that's why aircraft can be trimmed in flight. Small adjustments
are made to control position to correct for such variations in lift. Any
variation in schedules is minimal and can be absorbed by allowing a few
minuted extra in published arrival times, in addition most aircraft
(Concorde is an exception) do not travel at their maximum speed.
Headwinds and ATC delays contribute much more to late flights.

Hope this helps.

Mike