Re: AA changes rules after BDL incident

From:         "G. E. Lambert" <gedl@popd.ix.netcom.com>
Organization: Netcom
Date:         18 Dec 95 15:26:07 
References:   1
Followups:    1
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I picked up this thread way after the fact.  If the following is
redundant, my apologies.

It is my understanding that AA flies all approaches, visual and
instrument, using QFE altimeter settings.  If you know QNH, you can
compute QFE by subtracting elevation/1000 from it.  The advantage of QFE
is that your altimeter always reads approximately zero at touchdown.
(Approximately, because QFE is usually based on airport reference point
elevation rather than touchdown zone elevation.)  The disadvantage is
that someone has to do a calculation.  If that someone is the pilots, it
is an addtional burden during a stressful phase of flight.  If it is
someone else, the pilots are critically dependent on someone else's work,
although they can check it.

I understand that AA approaches are flown with both pilot's altimeters
set to QFE and the standby altimeter set to QNH. They approach is then
flown with respect to the HAA numbers shown in parentheses on the
Jeppesen charts.  Could the crew have been given an incorrect QFE and not
picked up the error on their standby?  Could their standby have been
sufficiently in error that the error was not caught?  Could the QNH been
flat out wrong with the resultant QFE in error?  Where was the GPWS in
this event?  What did the radio altimeter(s) show?  Did the crew
overshoot the MDA?  It will be interesting to read the NTSB report.

To add to the chorus,  visibility is the required minimum, almost without
exception, in the United States.  Ceiling reports are notoriously
unreliable, in my experience.

G. E. Lambert
Ann Arbor