Re: Are commuter aircrafts really that disliked ?

From:         "A. Kevin Rodriguez" <AKRodriguez@TASC.COM>
Organization: TASC
Date:         06 Nov 95 14:28:57 
References:   1 2 3 4 5
Next article
View raw article
  or MIME structure

Ed Hahn wrote:
>
> In article <airliners.1995.1701@ohare.Chicago.COM>
tskono@ucdavis.edu (Timothy Kono) writes:
>
>    Robert Ashcroft (rna@gsb-pound.stanford.edu) wrote:
>    : In article <45n0oe$d9n@pipe6.nyc.pipeline.com>,
>    : Michael Coch <beekman@pipeline.com> wrote:
>
>    : >There are pros and cons to everything.  According to my pilot friends, you
>    : >don't want to be in a light jet during landing if there's wind shear --
>    : >takes a little too long for the engines to spool up to counter the shear.
>
> velocities.  An ASCIIgram of the cross section (use fixed width font
> for best results):
>
>       ||| <-Descending air
>       |||
>       /|\
>    \--/|\--/  <- flattening and "rollup" near the ground ( < 2000 ft AGL)
> ================= <- the ground
>
> In the typical "hazard" case, the aircraft is flying an
> approach only

Back in the late 80's I did some ATC transcription for my
ofice mate who was doing an operational evaluation of Terminal
Doppler Weather Radar (TDWR) for the FAA.  My experience in
hearing the pilots and comparing this to the TDWR read-outs
follows.  Most, if not all, of the events recorded were
transport a/c (e.g., B737, MD80, etc.).  The evaluation was
conducted at Denver Stapleton.  Note that I use ground speed
since there are drastic wind changes and, not knowing the
correct terms, refer to ground speed as a point of reference
for linear velocity.  I'm sure those of you who can will
straighten me out.

The initial entry into the microbusrt give the a/c a headwind
accompanied with an updraft.  This has the tendancy to reduce
the a/c's ground speed and rise above the glide slope of the
ILS.  In the past, no longer I believe, the pilots would want
to continue the approach and would fight the updraft to keep
the glide slope.  They would not abort the approach.  They
would then enter the horizontal out-draft of the micro burst
if they were low enough.  This would be an increased headwind
further reducing ground speed.  The a/c will then enter the
down-draft.  There will no longer be a head wind.  The a/c
will then begin to sink below the glide-slope.  The initial
problem would be the configuration of the a/c for the updraft.
Some pilots would continue the approach if they could maintain
the center-line and the glide slope.  The next phase would be
entry into the far-side out-draft.  This is if speed had
deteriorated significantly, stall was a real possibility.
Depending upon the techniques of the pilot, theamount of
airspeed maintained or increased in the down-draft would
determine how close they came to a stall situation.

There were no accidents while the evaluation took place.  The
closest an a/c came to the ground was ~ 300 ft. AGL (outside
the outer marker).  The TDWR technology is the windshear alert
system which is now being installed at airports.  The most
confusing part of the whole thing to me is the failure to read
the initial up-draft.  If the up-draft is taken as an
indicator of what's to come, then the pilot would increase
power, abort the approach, and not try to stay on the
glide-slope.  Certainly the most important issue, IMHO, was to
abort.  Trying to stay on the glide-slope forced the pilot to
configure the aircraft for the existing conditions and that
configuration was the worst thing for the next segment of the
micro.  Those initial seconds to change configuration were the
most important.

I would agree with the previous posters that the pilot has the
most to do with a windshear being an uncomfortable situation.
Is there anyone who could shead some light on the impacts of
engine spooling, and aircraft size on surviving windshear
(beyond that previously stated)?
__________________________________________
A. Kevin Rodriguez  (AKRodriguez@TASC.com)
The Analytic Sciences Corporation (TASC)
Reading, Massachusetts