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Completing the Non-precision approach as a Visual Approach



 
 
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  #41  
Old November 19th 03, 08:50 PM
Michael
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"John Clonts" wrote
Thanks, this is as I hoped. Somewhere along the way I had picked up a
suspicion that I couldn't legally descend from MDA until aligned with the
runway.


This is often taught as normal procedure but (1) it's not regulatory
and (2) on most circling approaches to minimums (meaning visibility
minimums) it's either dangerous or just plain unworkable.

Look at it this way - the visibility min on most circling approaches
is 1 sm. That means that in order to keep the runway in sight, you
can't ever get more than a mile from it. That means that your pattern
will be 3/4 mile wide, max, if you're not going to exceed 1 sm from
the runway when turning base. That means that when you turn final,
you have 3/4 of a mile to get down, max. On a 4 degree glideslope
(which is about the steepest I would recommend in low vis) that's 300
ft. On a 7 degree glideslope (which is normal power-off 10:1 glide
for a light single) that's barely over 500 ft. Circling minimums are
usually higher than 500 ft. Does that mean you're going to slip down
final with a mile of vis? Are you planning on trying this trick at
night too?

Personally, I recommend starting the descent early enough that you can
maintain a constant and comfortable 3 degree descent (about 500 fpm at
90 kts) all the way to touchdown.

When the sky is blue, it's no big deal to pull the power to idle, roll
into a maximum effort slip, get down, roll out just before the flare,
and put it on the numbers. Any reasonably competent VFR pilot should
be able to do it. When visibilities drop below 2 miles, especially at
night, with rain and mist, or both, it's really not a good idea. The
subtle visual cues that form the true basis for "seat of the pants"
flying are gone. As a rule of thumb, if you wouldn't maneuver that
way in IMC, don't do it when the vis is less than 2 miles.

2) Once I get to class G airspace on my approach and am clear of

clouds
in
1 mi vis, can I then descend below MDA by doing something like declaring
myself visual, contact, or canceled IFR.


If you are actually in Class G and have 1 mile and clear of clouds,
you can cancel IFR. IMO this is a suboptimal procedure.

For example, suppose that an airplane is holding for release. The
moment you cancel IFR, the controller will release it. If you are
operating at low altitude in minimum visibility near the airport, do
you really want company?

A visual approach requires VFR minimums to be issued. I believe you
need 3 miles of visibility for that.

A contact approach is fine with 1 mile and clear of clouds, and can be
issued in controlled airspace. However, if you can see the runway,
you don't need a contact approach. On the other hand, if you can't
see the runway but can see the ground, are familiar with the area,
know where you are, and are confident you can fly to the airport
visually while remaining clear of clouds and maintaining 1 mile flight
visibility, a contact approach is the way to go.

Michael
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  #42  
Old November 19th 03, 11:15 PM
Steven P. McNicoll
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wrote in message
...

Your usual fine observations aside, as you well know some IAPs with
circling-only minimums are aligned exactly with a runway but don't have
straight-in minimums because of descent gradient requirements.


This ain't one of 'em.



They are set forth in 91.175 as you well know.


They? Hmmmm.... They, third-person plural pronoun, hmmmm...... I can find
only one reference to circle-to-land in FAR 91.175, and it doesn't apply
below the MDA.


91.175 Takeoff and landing under IFR.

(e) Missed approach procedures. Each pilot operating an aircraft, except a
military aircraft of the United States, shall immediately execute an
appropriate missed approach procedure when either of the following
conditions exist:

(2) Whenever an identifiable part of the airport is not distinctly
visible
to the pilot during a circling maneuver at or above MDA, unless the
inability to see an identifiable part of the airport results only from a
normal bank of the aircraft during the circling approach.


  #43  
Old November 20th 03, 02:30 AM
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I'm with you on this one Frank. On a circling or straight in
approach, I dont see how a pilot can descend below the mda, to 100 ft
above the airport, level off, and still claim he is "continuously" in
a position from which a descent can be made "at a normal rate". Who
"normally" makes a descent to land at less than, say, 2 1/2 degrees?
The far could be better worded, I admit. However, I've never seen
anyone descend at say 1 degree, which an early descent well prior to a
VDP would entail.

91.175(c)Operation below DH or MDA. Where a DH or MDA is applicable,
no pilot may operate an aircraft ... at any airport below the
authorized MDA ... unless

(1) The aircraft is continuously in a position from which a descent to
a landing on the intended runway can be made at a normal rate of
descent using normal maneuvers...

my ramblings, Stan




On 18 Nov 2003 16:47:32 -0500, (Frank Ch. Eigler)
wrote:


"John Clonts" writes:

[...] 1) Does "having the runway environment in sight...make a
normal landing" in 91.175 mean its ok to descend below MDA, fly a
couple more miles to the airport and then fly the pattern (circle to
land), as long as the runway is still in sight. [...]


One thing that troubles me about this is your reference to
circling-to-land. Up here in Canada, the IFR rules say that a descent
from the MDA for circling can only be done at the "final descent for
landing" - basically for the final approach. (I believe there is a
similar restriction for straight-in landings too.)

Look at it another way. If there was no prohibition against
descending below the MDA in this circumstance, what would keep a pilot
from going to 100 AGL at the earliest hole through the clouds, and
skirting the ground all the way to the airport? You are obviously
leaving all the IAP obstruction clearance margins, but are not making
that explicit by requesting a contact approach. That doesn't sound
right.

- FChE


  #44  
Old November 20th 03, 03:34 AM
John Clonts
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"Michael" wrote in message
om...
"John Clonts" wrote
Thanks, this is as I hoped. Somewhere along the way I had picked up a
suspicion that I couldn't legally descend from MDA until aligned with

the
runway.


This is often taught as normal procedure but (1) it's not regulatory
and (2) on most circling approaches to minimums (meaning visibility
minimums) it's either dangerous or just plain unworkable.

Look at it this way - the visibility min on most circling approaches
is 1 sm. That means that in order to keep the runway in sight, you
can't ever get more than a mile from it. That means that your pattern
will be 3/4 mile wide, max, if you're not going to exceed 1 sm from
the runway when turning base. That means that when you turn final,
you have 3/4 of a mile to get down, max. On a 4 degree glideslope
(which is about the steepest I would recommend in low vis) that's 300
ft. On a 7 degree glideslope (which is normal power-off 10:1 glide
for a light single) that's barely over 500 ft. Circling minimums are
usually higher than 500 ft. Does that mean you're going to slip down
final with a mile of vis? Are you planning on trying this trick at
night too?

Personally, I recommend starting the descent early enough that you can
maintain a constant and comfortable 3 degree descent (about 500 fpm at
90 kts) all the way to touchdown.

When the sky is blue, it's no big deal to pull the power to idle, roll
into a maximum effort slip, get down, roll out just before the flare,
and put it on the numbers. Any reasonably competent VFR pilot should
be able to do it. When visibilities drop below 2 miles, especially at
night, with rain and mist, or both, it's really not a good idea. The
subtle visual cues that form the true basis for "seat of the pants"
flying are gone. As a rule of thumb, if you wouldn't maneuver that
way in IMC, don't do it when the vis is less than 2 miles.

2) Once I get to class G airspace on my approach and am clear of

clouds
in
1 mi vis, can I then descend below MDA by doing something like

declaring
myself visual, contact, or canceled IFR.


If you are actually in Class G and have 1 mile and clear of clouds,
you can cancel IFR. IMO this is a suboptimal procedure.

For example, suppose that an airplane is holding for release. The
moment you cancel IFR, the controller will release it. If you are
operating at low altitude in minimum visibility near the airport, do
you really want company?

A visual approach requires VFR minimums to be issued. I believe you
need 3 miles of visibility for that.

A contact approach is fine with 1 mile and clear of clouds, and can be
issued in controlled airspace. However, if you can see the runway,
you don't need a contact approach. On the other hand, if you can't
see the runway but can see the ground, are familiar with the area,
know where you are, and are confident you can fly to the airport
visually while remaining clear of clouds and maintaining 1 mile flight
visibility, a contact approach is the way to go.

Michael


Excellent elaborations as usual, thanks!

John


  #45  
Old November 20th 03, 05:54 AM
Snowbird
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"John Clonts" wrote in message .. .
1) Does "having the runway environment in sight...make a normal landing"
in 91.175 mean its ok to descend below MDA, fly a couple more miles to the
airport and then fly the pattern (circle to land), as long as the runway is
still in sight.


FWIW, that's my understanding. If you have the vis and you have the
runway environment clearly in sight. Just realize that circling is
tricky, and descending then circling doesn't make it less tricky.
Also, if the cloud deck is ragged and you lose the airport, what's
your plan for how low you will go to stay visual? The "MDA"
gives you a firm floor until you have the airport and the vis.
Once you start your descent, if you're far enough from the airport
that you might realistically lose it if conditions change a mite,
what's your personal "floor" and how did you choose it?

2) Once I get to class G airspace on my approach and am clear of clouds in
1 mi vis, can I then descend below MDA by doing something like declaring

myself visual, contact, or canceled IFR.


Personally, if you have to descend below MDA to stay visual I
think I would vote for "none of the above". What if the cloud
deck is ragged and something rolls in, you have to go missed?
What if there's someone else waiting for the same approach? Or
another IFR waiting to be released?

I don't see what a contact approach gains you.

For visual approach you need 3 miles vis.

FWIW,
Sydney
  #46  
Old November 20th 03, 06:20 AM
Kobra
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A visual approach requires VFR minimums to be issued. I believe you
need 3 miles of visibility for that.


I think it depends on your AGL altitude. If you're below 1200' AGL outside
any magenta circles you only need 1mile vis. and inside the magenta circle
you would have to be below 700' AGL and only need 1 mile vis. If it was a
class E surface area then you would need 3 miles vis. to get in VFR. I
think.

Kobra



A contact approach is fine with 1 mile and clear of clouds, and can be
issued in controlled airspace. However, if you can see the runway,
you don't need a contact approach. On the other hand, if you can't
see the runway but can see the ground, are familiar with the area,
know where you are, and are confident you can fly to the airport
visually while remaining clear of clouds and maintaining 1 mile flight
visibility, a contact approach is the way to go.

Michael



 




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