AOPA Pilot Magazine - January 2017 - 92

P&E

ON INSTRUMENTS

How low can you go?
Runway in sight-or is it a shopping mall?

CHARLES FLOYD

BY THOMAS A. HORNE

THE WEATHER IS at minimums. You've passed the final
approach fix, completed the
necessary checklist items, and
are on your descent to what you
hope is a landing. You're dividing your time between scanning
your instruments and looking
outside. This can be dangerous,
as you're close to the ground,
and absolutely must stay on
course and glidepath. But at the
same time, you need to be able
to see the runway environment
in order to land legally.
Here's hoping that the
weather is on your side. If the
reported visibility at the airport
is below published minimums,
you may not be able to descend
below the decision altitude
(DA), decision height (DH),
or minimum descent altitude (MDA) for the approach
you're attempting. I'm saying
may because there are some
pretty big exceptions to that
rule. Exceptions that deal with
flight visibility-the visibility
as perceived from the cockpit-not ceiling or cloud-base
altitudes. Acceptable visibility
is what most of us are counting
on to make it to the runway.
This visibility assumes you're
on an approach path that puts
you continuously in a position
from which you can descend
to the runway at a normal rate,
and land within the touchdown
zone. We're obviously not talking about a situation where
you're below an approach's
vertical profile, dragging the

92 | AOPA PILOT January 2017

airplane up to the runway, facing the possibility of terrain or
obstacles, and hoping against
hope that the flight visibility is
better at low altitude.
First and foremost, it's
the pilot who makes the call
on visibility. After all, the visibility in a METAR-or from
sources such as an automated surface observation
system (ASOS), automated
weather observation system
(AWOS), or automatic terminal information service (ATIS)
installations-are ground
observations. It's reported by
automated sensors that sample
a small volume of air hugging
the surface-or, more precisely,
about six feet above the surface
in the case of ASOS equipment. This is all very helpful,
but what really matters is what
we can see on approach. If we
have one mile visibility on final
approach and an AWOS says
it's one-half mile-well, the
regulations say we may be able
to safely and legally continue
the approach; descend below
DA, DH, or MDA; and land.
There's that conditional
"may" again. It all depends on
what you see ahead. Ideally,
the visibility is good enough
to see the entire airport environment (which includes
the runway itself, plus any
approach lighting systems).
But in fog, heavy rain, snow-
especially at night-you may
not see the runway or its
threshold. The only things

IF THE PILOT on approach to a runway

served by ALSF-2 lighting can see the red
side row of lights, he or she can descend
below 100 feet above the runway
threshold light. Here, those lights are just
becoming visible, so a descent to the
runway is legal. With ALSF-1 lighting,
there are no side rows of red lights.



Table of Contents for the Digital Edition of AOPA Pilot Magazine - January 2017

https://www.nxtbook.com/nxtbooks/aopa/pilot_202404
https://www.nxtbook.com/nxtbooks/aopa/pilot_202403
https://www.nxtbook.com/nxtbooks/aopa/pilot_202402
https://www.nxtbook.com/nxtbooks/aopa/pilot_202401
https://www.nxtbook.com/nxtbooks/aopa/pilot_202312
https://www.nxtbook.com/nxtbooks/aopa/pilot_202311
https://www.nxtbook.com/nxtbooks/aopa/pilot_202310
https://www.nxtbook.com/nxtbooks/aopa/pilot_202309
https://www.nxtbook.com/nxtbooks/aopa/pilot_202308
https://www.nxtbook.com/nxtbooks/aopa/pilot_202307
https://www.nxtbook.com/nxtbooks/aopa/pilot_202306
https://www.nxtbook.com/nxtbooks/aopa/pilot_202305
https://www.nxtbook.com/nxtbooks/aopa/pilot_202304
https://www.nxtbook.com/nxtbooks/aopa/pilot_202303
https://www.nxtbook.com/nxtbooks/aopa/pilot_202302
https://www.nxtbook.com/nxtbooks/aopa/pilot_202301
https://www.nxtbook.com/nxtbooks/aopa/pilot_202212
https://www.nxtbook.com/nxtbooks/aopa/pilot_202211
https://www.nxtbook.com/nxtbooks/aopa/pilot_202210
https://www.nxtbook.com/nxtbooks/aopa/pilot_202209
https://www.nxtbook.com/nxtbooks/aopa/pilot_202208
https://www.nxtbook.com/nxtbooks/aopa/pilot_202207
https://www.nxtbook.com/nxtbooks/aopa/pilot_202206
https://www.nxtbook.com/nxtbooks/aopa/pilot_202205
https://www.nxtbook.com/nxtbooks/aopa/pilot_202204
https://www.nxtbook.com/nxtbooks/aopa/pilot_202203
https://www.nxtbook.com/nxtbooks/aopa/pilot_202202
https://www.nxtbook.com/nxtbooks/aopa/pilot_202201
https://www.nxtbook.com/nxtbooks/aopa/pilot_202112
https://www.nxtbook.com/nxtbooks/aopa/pilot_202111
https://www.nxtbook.com/nxtbooks/aopa/pilot_202110
https://www.nxtbook.com/nxtbooks/aopa/pilot_202109
https://www.nxtbook.com/nxtbooks/aopa/pilot_202108
https://www.nxtbook.com/nxtbooks/aopa/pilot_202107
https://www.nxtbook.com/nxtbooks/aopa/pilot_202106
https://www.nxtbook.com/nxtbooks/aopa/pilot_202105
https://www.nxtbook.com/nxtbooks/aopa/pilot_202104
https://www.nxtbook.com/nxtbooks/aopa/pilot_202103
https://www.nxtbook.com/nxtbooks/aopa/pilot_202102
https://www.nxtbook.com/nxtbooks/aopa/pilot_202101
https://www.nxtbook.com/nxtbooks/aopa/pilot_202012
https://www.nxtbook.com/nxtbooks/aopa/pilot_202011
https://www.nxtbook.com/nxtbooks/aopa/pilot_202010
https://www.nxtbook.com/nxtbooks/aopa/pilot_202009
https://www.nxtbook.com/nxtbooks/aopa/pilot_202008
https://www.nxtbook.com/nxtbooks/aopa/pilot_202007
https://www.nxtbook.com/nxtbooks/aopa/pilot_202006
https://www.nxtbook.com/nxtbooks/aopa/pilot_202005
https://www.nxtbook.com/nxtbooks/aopa/pilot_202004
https://www.nxtbook.com/nxtbooks/aopa/pilot_202003
https://www.nxtbook.com/nxtbooks/aopa/pilot_202002
https://www.nxtbook.com/nxtbooks/aopa/pilot_202001
https://www.nxtbook.com/nxtbooks/aopa/pilot_201912
https://www.nxtbook.com/nxtbooks/aopa/pilot_201911
https://www.nxtbook.com/nxtbooks/aopa/pilot_201910
https://www.nxtbook.com/nxtbooks/aopa/pilot_201909
https://www.nxtbook.com/nxtbooks/aopa/pilot_201908
https://www.nxtbook.com/nxtbooks/aopa/pilot_201907
https://www.nxtbook.com/nxtbooks/aopa/pilot_201906
https://www.nxtbook.com/nxtbooks/aopa/pilot_201905
https://www.nxtbook.com/nxtbooks/aopa/pilot_201904
https://www.nxtbook.com/nxtbooks/aopa/pilot_201903
https://www.nxtbook.com/nxtbooks/aopa/pilot_201902
https://www.nxtbook.com/nxtbooks/aopa/pilot_201901
https://www.nxtbook.com/nxtbooks/aopa/pilot_201812
https://www.nxtbook.com/nxtbooks/aopa/pilot_201811
https://www.nxtbook.com/nxtbooks/aopa/pilot_201810
https://www.nxtbook.com/nxtbooks/aopa/pilot_201809
https://www.nxtbook.com/nxtbooks/aopa/pilot_201808
https://www.nxtbook.com/nxtbooks/aopa/pilot_201807
https://www.nxtbook.com/nxtbooks/aopa/pilot_201806
https://www.nxtbook.com/nxtbooks/aopa/pilot_201805
https://www.nxtbook.com/nxtbooks/aopa/pilot_201804
https://www.nxtbook.com/nxtbooks/aopa/pilot_201803
https://www.nxtbook.com/nxtbooks/aopa/pilot_201802
https://www.nxtbook.com/nxtbooks/aopa/pilot_201801
https://www.nxtbook.com/nxtbooks/aopa/pilot_201712
https://www.nxtbook.com/nxtbooks/aopa/pilot_201711
https://www.nxtbook.com/nxtbooks/aopa/pilot_201710
https://www.nxtbook.com/nxtbooks/aopa/pilot_201709
https://www.nxtbook.com/nxtbooks/aopa/pilot_201708
https://www.nxtbook.com/nxtbooks/aopa/pilot_201707
https://www.nxtbook.com/nxtbooks/aopa/pilot_201706
https://www.nxtbook.com/nxtbooks/aopa/pilot_201705
https://www.nxtbook.com/nxtbooks/aopa/pilot_201704
https://www.nxtbook.com/nxtbooks/aopa/pilot_201703
https://www.nxtbook.com/nxtbooks/aopa/pilot_201702
https://www.nxtbook.com/nxtbooks/aopa/pilot_201701
https://www.nxtbook.com/nxtbooks/aopa/pilot_201612
https://www.nxtbook.com/nxtbooks/aopa/pilot_201611
https://www.nxtbook.com/nxtbooks/aopa/pilot_201610
https://www.nxtbook.com/nxtbooks/aopa/pilot_201609
https://www.nxtbook.com/nxtbooks/aopa/pilot_201608
https://www.nxtbook.com/nxtbooks/aopa/pilot_201607
https://www.nxtbook.com/nxtbooks/aopa/pilot_201606
https://www.nxtbook.com/nxtbooks/aopa/pilot_201605
https://www.nxtbook.com/nxtbooks/aopa/pilot_201604
https://www.nxtbook.com/nxtbooks/aopa/pilot_201603
https://www.nxtbook.com/nxtbooks/aopa/pilot_201602
https://www.nxtbook.com/nxtbooks/aopa/pilot_201601
https://www.nxtbook.com/nxtbooks/aopa/pilot_201512
https://www.nxtbook.com/nxtbooks/aopa/pilot_201511
https://www.nxtbook.com/nxtbooks/aopa/pilot_201510
https://www.nxtbook.com/nxtbooks/aopa/pilot_201509
https://www.nxtbook.com/nxtbooks/aopa/pilot_201508
https://www.nxtbook.com/nxtbooks/aopa/pilot_201507
https://www.nxtbook.com/nxtbooks/aopa/pilot_201506
https://www.nxtbook.com/nxtbooks/aopa/pilot_201505
https://www.nxtbook.com/nxtbooks/aopa/pilot_201504
https://www.nxtbook.com/nxtbooks/aopa/pilot_201503
https://www.nxtbook.com/nxtbooks/aopa/pilot_201502
https://www.nxtbook.com/nxtbooks/aopa/pilot_201501
https://www.nxtbook.com/nxtbooks/aopa/pilot_201412
https://www.nxtbook.com/nxtbooks/aopa/pilot_201411
https://www.nxtbook.com/nxtbooks/aopa/pilot_201410
https://www.nxtbook.com/nxtbooks/aopa/pilot_201409
https://www.nxtbook.com/nxtbooks/aopa/pilot_201408
https://www.nxtbook.com/nxtbooks/aopa/pilot_201407
https://www.nxtbook.com/nxtbooks/aopa/pilot_201406
https://www.nxtbook.com/nxtbooks/aopa/pilot_201405
https://www.nxtbook.com/nxtbooks/aopa/pilot_201404
https://www.nxtbook.com/nxtbooks/aopa/pilot_201403
https://www.nxtbook.com/nxtbooks/aopa/pilot_201402
https://www.nxtbook.com/nxtbooks/aopa/pilot_201401
https://www.nxtbook.com/nxtbooks/aopa/pilot_201312
https://www.nxtbook.com/nxtbooks/aopa/pilot_201311
https://www.nxtbook.com/nxtbooks/aopa/pilot_201310
https://www.nxtbook.com/nxtbooks/aopa/pilot_201309
https://www.nxtbook.com/nxtbooks/aopa/pilot_201308
https://www.nxtbook.com/nxtbooks/aopa/pilot_201307
https://www.nxtbook.com/nxtbooks/aopa/pilot_201306
https://www.nxtbook.com/nxtbooks/aopa/pilot_201305
https://www.nxtbook.com/nxtbooks/aopa/pilot_201304
https://www.nxtbook.com/nxtbooks/aopa/pilot_201303
https://www.nxtbook.com/nxtbooks/aopa/pilot_201302
https://www.nxtbook.com/nxtbooks/aopa/pilot_201301
https://www.nxtbook.com/nxtbooks/aopa/pilot_201212
https://www.nxtbook.com/nxtbooks/aopa/pilot_201211
https://www.nxtbook.com/nxtbooks/aopa/pilot_201210
https://www.nxtbook.com/nxtbooks/aopa/pilot_201209
https://www.nxtbook.com/nxtbooks/aopa/pilot_201208
https://www.nxtbook.com/nxtbooks/aopa/pilot_201207
https://www.nxtbook.com/nxtbooks/aopa/pilot_201206
https://www.nxtbook.com/nxtbooks/aopa/pilot_201205
https://www.nxtbook.com/nxtbooks/aopa/pilot_201204
https://www.nxtbook.com/nxtbooks/aopa/pilot_201203
https://www.nxtbook.com/nxtbooks/aopa/pilot_201202
https://www.nxtbook.com/nxtbooks/aopa/pilot_201201
https://www.nxtbook.com/nxtbooks/aopa/pilot_201112
https://www.nxtbook.com/nxtbooks/aopa/pilot_201111
https://www.nxtbook.com/nxtbooks/aopa/pilot_201110
https://www.nxtbook.com/nxtbooks/aopa/pilot_201109
https://www.nxtbook.com/nxtbooks/aopa/pilot_201108
https://www.nxtbook.com/nxtbooks/aopa/pilot_201107
https://www.nxtbook.com/nxtbooks/aopa/pilot_201106
https://www.nxtbook.com/nxtbooks/aopa/pilot_201105
https://www.nxtbook.com/nxtbooks/aopa/pilot_201104
https://www.nxtbook.com/nxtbooks/aopa/pilot_201103
https://www.nxtbook.com/nxtbooks/aopa/pilot_201103_test
https://www.nxtbook.com/nxtbooks/aopa/pilot_201102
https://www.nxtbook.com/nxtbooks/aopa/pilot_201011demo
https://www.nxtbook.com/nxtbooks/aopa/pilot_201011
https://www.nxtbook.com/nxtbooks/aopa/pilot0308
https://www.nxtbookmedia.com