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Established on the approach - Checkride question



 
 
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  #1  
Old September 29th 03, 04:28 PM
endre
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Default Established on the approach - Checkride question

I did my instrument checkride the other day and passed...

Question for this group.

I was being radar vectored for the SHN NDB approach. I was cleared in
the following way: Cessna 61786 14 miles from NDB descend and maintain
2000 until established.

The problem: I was outside the 10 mile ring on the plate, established
on the inbound course, no way to tell when I would be inside 10 mile.
However, I would need to descend to 1400 before the NDB to have a
chance to descend to MDA of 900.

What would you all do?

Endre
  #2  
Old September 29th 03, 05:02 PM
Aarfy
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I'd look at my GNS430 and start descending to 1400' at CARRO or 10nm from
the NDB.

My read of the plate says that on the approach course you need to be at
1900' 10nm from the NDB. If you don't have an approach-ready GPS then I
guess there's 2 ways to go:

1. Calculate/estimate your ground speed, and use a timer to figure out when
you've traveled 4nm to be within 10nm, begin descent to 1400'.
2. Ask ATC to give you a heads-up when you're 10nm out, begin descent to
1400'.

Then again, maybe I'm reading the plate wrong.....



"endre" wrote in message
om...
I did my instrument checkride the other day and passed...

Question for this group.

I was being radar vectored for the SHN NDB approach. I was cleared in
the following way: Cessna 61786 14 miles from NDB descend and maintain
2000 until established.

The problem: I was outside the 10 mile ring on the plate, established
on the inbound course, no way to tell when I would be inside 10 mile.
However, I would need to descend to 1400 before the NDB to have a
chance to descend to MDA of 900.

What would you all do?

Endre



  #3  
Old September 29th 03, 05:13 PM
Greg Esres
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I was outside the 10 mile ring on the plate

I would first point out that that the 10 mile ring is irrelevant. The
ring depicted on NACO charts is NOT the procedure turn area. It
merely says everything is to scale inside the ring. Common
misunderstanding, but an instrument instructor should be slapped
around if he teaches it.

The only "10 nm" that comes into play is the one on the profile file
that says "remain within 10 nm". The protected area for a PT is NOT
a circle; more like an egg.



  #4  
Old September 29th 03, 06:11 PM
David Megginson
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(endre) writes:

I was being radar vectored for the SHN NDB approach. I was cleared
in the following way: Cessna 61786 14 miles from NDB descend and
maintain 2000 until established.

The problem: I was outside the 10 mile ring on the plate, established
on the inbound course, no way to tell when I would be inside 10 mile.
However, I would need to descend to 1400 before the NDB to have a
chance to descend to MDA of 900.

What would you all do?


Since you were being vectored and not flying a full procedure, I'd
guess that you were OK to descend as soon as you intercepted the
inbound course, but if in doubt I would have asked ATC to clarify (as
I often do -- better embarrassed than dead). In my real-life IFR
flying so far, I've noticed that ATC often vectors me onto the
approach path far out beyond the PT limits -- once so far that I could
just barely pick up the localizer (in night IMC no less) -- and that
they intend for me to follow any altitude instructions as soon as I'm
on the course, even if I won't be inside PT limits for another 10
minutes or more.

Even if my experience is unusual (or U.S. ATC works differently, and
"established" means explicitly "inside PT limits"), they still gave
you the information you needed -- you were 14 nm from the NDB, and
with a 90 kias approach speed, 3 minutes (4 with a strong headwind)
should have been good enough to ensure that you were inside the 10 nm
circle.


All the best,


David
  #5  
Old September 29th 03, 06:27 PM
Greg Esres
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I'd guess that you were OK to descend as soon as you intercepted the
inbound course,

Argh! No! The PILOT must know when he's established and within the
protected area. All you've intercepted is a navaid, not a segment of
the approach, until you've reached the start of that segment.

they intend for me to follow any altitude instructions as soon as
I'm on the course, even if I won't be inside PT limits for another 10
minutes or more.

What ATC intends is irrelevant. If they want you at the published
altitude before you reached the point where that altitude applies,
then they're got to clear you down to it, using their MVAs.

Failure to understand this concept has killed some people in the past,
including at least 1 airliner, TWA 514.

See the AOPA article:

http://www.aopa.org/asf/asfarticles/sp9806.html


  #6  
Old September 29th 03, 06:32 PM
McGregor
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Well, is the 10 nm ring irrelevent if he's already on the inbound course?

If he's getting "vectors to final" then he's not expected to make a PT.
Presumably he's going to be close to or on the final approach course when
ATC clears him 14 miles out.

There is another IAF 9.7 nm out and slightly left of course at CARRO which
allows you to descend to 1400 (and skip the PT). Even if it weren't there,
I'd be tempted to descend to 1400 inside 10nm. If you're on the final
approach course and inside the PT limits... why not?

Anyway, I'd start a timer after ATC said "cleared for the approach." If
you're going 120 knots wait for 2 minutes and then begin your descent to
1400 feet.

If you're good at trigonometry (I'm not, I'm not even sure I can spell it)
then you could use the OLM VOR for a DME fix. It's 18.2 to the NDB, and 90
degrees right of the 317 radial is 047, which is pretty close to (the
reciprocal of) your inbound course... so using Pythagorus's theorem you can
solve for the DME reading you need to see from OLM while on the inbound
course to know you're 10 (or 9.7) miles out. I get 20.6 - a nice thing to do
on the ground so you don't have to do square roots in your head while flying
an approach.


"Greg Esres" wrote in message
...
I was outside the 10 mile ring on the plate

I would first point out that that the 10 mile ring is irrelevant. The
ring depicted on NACO charts is NOT the procedure turn area. It
merely says everything is to scale inside the ring. Common
misunderstanding, but an instrument instructor should be slapped
around if he teaches it.

The only "10 nm" that comes into play is the one on the profile file
that says "remain within 10 nm". The protected area for a PT is NOT
a circle; more like an egg.





  #7  
Old September 29th 03, 06:47 PM
Gary L. Drescher
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"Greg Esres" wrote in message
...
I'd guess that you were OK to descend as soon as you intercepted the
inbound course,

Argh! No! The PILOT must know when he's established and within the
protected area. All you've intercepted is a navaid, not a segment of
the approach, until you've reached the start of that segment.


Is it well-defined where the approach segment begins when you're vectored
for SHN NDB-A? (There's an IAF at CARRO, but it's a bit to the side of the
approach course.)

--Gary


  #8  
Old September 29th 03, 06:47 PM
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Greg Esres wrote:

I'd guess that you were OK to descend as soon as you intercepted the
inbound course,

Argh! No! The PILOT must know when he's established and within the
protected area. All you've intercepted is a navaid, not a segment of
the approach, until you've reached the start of that segment.

they intend for me to follow any altitude instructions as soon as
I'm on the course, even if I won't be inside PT limits for another 10
minutes or more.

What ATC intends is irrelevant. If they want you at the published
altitude before you reached the point where that altitude applies,
then they're got to clear you down to it, using their MVAs.

Failure to understand this concept has killed some people in the past,
including at least 1 airliner, TWA 514.


Your points are all right on. Having said that, this thread demonstrates
that, 29 years after TWA 514, both pilots and controllers do not fully
understand this stuff. The clearance for that NDB approach with "until
established" is a "setup" by ATC; albeit from lack of controller
understanding. Over the years since the TWA 514 crash the controller's
handbook has had many layers of "inner tube" patches on the area of radar
vectors to approach procedures. The only correct clearance for such a
vector to the PT area, would be for the controller to withhold approach
clearance, using MVAs, until the aircraft is within 10 miles of the PT
fix. But, this is simply not taught to controllers. The burden for this
one should be on ATC, not the pilot.

  #9  
Old September 29th 03, 06:51 PM
David Megginson
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Greg Esres writes:

I'd guess that you were OK to descend as soon as you intercepted
the inbound course,

Argh! No! The PILOT must know when he's established and within the
protected area. All you've intercepted is a navaid, not a segment
of the approach, until you've reached the start of that segment.


It's a little different here, because MSA is operational -- we have an
altitude we can descend to as soon as we're within 25 nm.

(Note that you snipped out the part where I said I'd call and check
what they actually wanted.)


Thanks for the info,


David

  #10  
Old September 29th 03, 06:53 PM
Greg Esres
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Is it well-defined where the approach segment begins when you're
vectored for SHN NDB-A?

Yes, in theory. ;-) You're on the final approach segment where the
initial segment intersects the final approach course at (or within)
the 10 nm limit stated in the chart.

How you would detect this on a vectors to final outside this limit is
point of the original poster. I never waste NDB approaches by doing
vectors to final, so I haven't given any thought to the issue. ATC
probably ought not to do what they did, but I'm not aware of any rules
stating such.

 




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