descent below minimums

It would probably help if it was explained how the MDA is established by
AVN.
First, the MDA is established between the FAF and MAP/threshold
(whichever is last). This is the basic MDA for the procedure.
Second, the specialist will determine if it's possible to provide a
lower MDA at some point on final by adding another fix after the FAF
where the pilot can "step down" to a lower altitude. This can only be
done if there is either at least a 60 ft reduction in the MDA, or a
reduction in visibility.
Third, there has to be a suitable fix to be used as a stepdown.

If the above criteria is met, then the specialist can add a lower MDA
that is applicable after the stepdown fix. Whether the first MDA is
actually listed as an MDA in the minimums section is dependent on
whether the stepdown fix will "always" be received, or if it will only
be received by some aircraft. For RNAV (GPS) approaches, it's considered
to always be receivable by the aircraft, so only the one MDA is
published as an MDA. If it's a procedure with /DME in the procedure
name, then it's also considered always receivable by the aircraft, since
you're required to have DME to conduct the procedure due to the
procedure title.

For other procedures, such as a VOR or LOC or NDB (not xxx/DME) with a
DME or crossing radial/bearing stepdown fix, the stepdown altitude will
also be shown as the MDA, since it is the MDA for those aircraft not
capable of receiving the stepdown fix. In those cases, you will see 2
MDA's published on the procedure, since some aircraft can't benefit from
the lower MDA.

You're right, the MDA is the lowest altitude, expressed in MSL, to which
descent is authorized on final approach. And the lowest altitude,
expressed in MSL, to which descent is authorized on final prior to the
stepdown fix is the minimum altitude shown at the stepdown fix. That is
your MDA until you reach the stepdown fix.

The complication is that the selected altitude may be computed
differently depending on whether it's "always received" or just
"sometimes received". If it can only be received sometimes, it will
actually be the lowest altitude that will clear obstructions on that
segment of final between the FAF and stepdown fix. This is to benefit
those that won't be able to receive the stepdown fix.
If it can always be received, it may be artificially adjusted higher for
various reasons (provide an optimum descent gradient, provide a 300'
buffer above the floor of controlled airspace, ensure NAVAID reception
in an otherwise poor reception area, give an even 100' increment
altitude, etc)

There's an example of what can happen when an aircraft descends below
the stepdown altitude on final (and also below the MDA) at this website.
http://www.avweb.com/news/airman/184931-1.html
This particular aircraft had reported the runway in sight prior to the
stepdown fix and about a minute before he impacted rising terrain on final.


JPH

Ron Rosenfeld wrote:
On Wed, 05 Jan 2005 16:05:08 -0600, J Haggerty
wrote:


The minimum altitude prior to reaching the stepdown fix is also the MDA
unless and until the stepdown fix is received.


You must be looking at a different P/C glossary than I am:

MINIMUM DESCENT ALTITUDE- The lowest altitude, expressed in feet above mean
sea level, to which descent is authorized on final approach or during
circle-to-land maneuvering in execution of a standard instrument approach
procedure where no electronic glideslope is provided.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

wrote in news:hknmt05hfh1ie353a9nm8or71cnfclhn64@
4ax.com:

On Tue, 04 Jan 2005 18:09:11 -0500, Matt Whiting
wrote:

Roy Smith wrote:

In article ,
wrote:

On Tue, 04 Jan 2005 09:16:52 -0500, Roy Smith wrote:


For example, at night, the runway might be lit up like
a christmas tree, but the hills might be invisible.


If you can see the runway, there ain't no hill between you and it.


But there can still be a hill below for you to descend into. Your
eyeballs can still have clear line of sight to the runway lights
while
your landing gear is dragging through the treetops.

Or the runway could be in a valley with a high tension line across
it...


Matt


Like I said.

If you can see the runway, there ain't no hill between you and it.


Yea, but a power line is just as bad as a hill.

In article ,
Andrew Sarangan wrote:

wrote in news:hknmt05hfh1ie353a9nm8or71cnfclhn64@
4ax.com:

On Tue, 04 Jan 2005 18:09:11 -0500, Matt Whiting
wrote:

Roy Smith wrote:

In article ,
wrote:

On Tue, 04 Jan 2005 09:16:52 -0500, Roy Smith wrote:


For example, at night, the runway might be lit up like
a christmas tree, but the hills might be invisible.


If you can see the runway, there ain't no hill between you and it.


But there can still be a hill below for you to descend into. Your
eyeballs can still have clear line of sight to the runway lights
while
your landing gear is dragging through the treetops.

Or the runway could be in a valley with a high tension line across
it...


Matt


Like I said.

If you can see the runway, there ain't no hill between you and it.


Yea, but a power line is just as bad as a hill.

Not really. With a power line, you at least stand a chance of just
catching the wire with the landing gear and ending up hanging upside
down from the gear until the firemen come and rescue you with a cherry
picker. It's hard to do that with a hill.

Roy Smith wrote in news:roy-0F407F.23230406012005
@reader1.panix.com:

In article ,
Andrew Sarangan wrote:

wrote in news:hknmt05hfh1ie353a9nm8or71cnfclhn64
@
4ax.com:

On Tue, 04 Jan 2005 18:09:11 -0500, Matt Whiting
wrote:

Roy Smith wrote:

In article ,
wrote:

On Tue, 04 Jan 2005 09:16:52 -0500, Roy Smith
wrote:


For example, at night, the runway might be lit up like
a christmas tree, but the hills might be invisible.


If you can see the runway, there ain't no hill between you and
it.


But there can still be a hill below for you to descend into.
Your
eyeballs can still have clear line of sight to the runway lights
while
your landing gear is dragging through the treetops.

Or the runway could be in a valley with a high tension line across
it...


Matt


Like I said.

If you can see the runway, there ain't no hill between you and it.


Yea, but a power line is just as bad as a hill.

Not really. With a power line, you at least stand a chance of just
catching the wire with the landing gear and ending up hanging upside
down from the gear until the firemen come and rescue you with a cherry
picker. It's hard to do that with a hill.


I wonder how often that really happens. I know of only one case when a
Seattle pilot hung on a wire. I would imagine that the chance of hitting
a wire and hanging upside down is just as remote as surviving a midair
collision. I could be wrong though.

On 6 Jan 2005 21:51:54 -0600, Andrew Sarangan
wrote:

wrote in news:hknmt05hfh1ie353a9nm8or71cnfclhn64@
4ax.com:

On Tue, 04 Jan 2005 18:09:11 -0500, Matt Whiting
wrote:

Roy Smith wrote:

In article ,
wrote:

On Tue, 04 Jan 2005 09:16:52 -0500, Roy Smith wrote:


For example, at night, the runway might be lit up like
a christmas tree, but the hills might be invisible.


If you can see the runway, there ain't no hill between you and it.


But there can still be a hill below for you to descend into. Your
eyeballs can still have clear line of sight to the runway lights
while
your landing gear is dragging through the treetops.

Or the runway could be in a valley with a high tension line across
it...


Matt


Like I said.

If you can see the runway, there ain't no hill between you and it.


Yea, but a power line is just as bad as a hill.


Like I said,

If youcan see the runway, there ain't no hill between you and it

On 6 Jan 2005 23:06:12 -0600, Andrew Sarangan
wrote:

I wonder how often that really happens. I know of only one case when a
Seattle pilot hung on a wire. I would imagine that the chance of hitting
a wire and hanging upside down is just as remote as surviving a midair
collision. I could be wrong though.




Remote? The survival rate is something like 30-40%, I believe. For
example, in 2000 there were 19 midairs, with 8 non-fatal. I don't
have the actual number of people involved.

On Thu, 06 Jan 2005 21:42:04 -0600, J Haggerty
wrote:

then the specialist can add a lower MDA
that is applicable after the stepdown fix. Whether the first MDA is
actually listed as an MDA in the minimums section is dependent on
whether the stepdown fix will "always" be received, or if it will only
be received by some aircraft. For RNAV (GPS) approaches, it's considered
to always be receivable by the aircraft, so only the one MDA is
published as an MDA. If it's a procedure with /DME in the procedure
name, then it's also considered always receivable by the aircraft, since
you're required to have DME to conduct the procedure due to the
procedure title.

There seems to be a disconnect between TERPs, training, AIM, etc. Not that
that is unusual.

Your explanation is clear.

However, as I mentioned in a later post, it reinforces the idea that it is
legal to descend below a SDF that occurs after the FAF, provided the
requirements of 91.175 are met.

This particular aircraft had reported the runway in sight prior to the
stepdown fix and about a minute before he impacted rising terrain on final.

First of all what is safe is not necessarily legal.

In the particular instance you cite, according to the report, the crew
flying was not following procedures that had been set up for the safe
operation of this aircraft. And, from the recordings, it does not appear
as if they really met all of the requirements of 91.175 before they
descended below the MDA.

Taking shortcuts (not following proper procedures) at an airport like Aspen
is fraught with hazard, moreso than at flatland airports.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

wrote in news:mevst09cot7rjsflpa7nucm8qa1nu4fijk@
4ax.com:

Like I said,

If youcan see the runway, there ain't no hill between you and it

But if you descend below the current angle of sight, there may be. You
might be looking just barely over the top of one.

--
Regards,

Stan

On 6 Jan 2005 23:06:12 -0600, Andrew Sarangan
wrote:



Not really. With a power line, you at least stand a chance of just
catching the wire with the landing gear and ending up hanging upside
down from the gear until the firemen come and rescue you with a cherry
picker. It's hard to do that with a hill.


I wonder how often that really happens. I know of only one case when a
Seattle pilot hung on a wire. I would imagine that the chance of hitting
a wire and hanging upside down is just as remote as surviving a midair
collision. I could be wrong though.

The odds aren't very good.
I personally know of 4 instances which is probably a small percentage,
but:

A 172 flying up a lake which turns into a river (Sanford Lake about 5
miles from me) hit a power line crossing the river (narrow section).
It tore the seats right out of the plane. No survivors. (2)

A year ago a friend and crop duster for many years took vertical stab
right off his ag plane. He got it away from the buildings along the
road but turned it into a law dart out in a field. No survivor. (1)

Some years back a Cherokee was coming into Tampa Bay Exec. It was
early morning fog and he must have been trying to get under it. He
hit the high tension lines two miles to the West of the airport. The
only thing left was the engine and looked like a piece of modeling
clay that some one had tried to roll into a ball. No survivor. (1)

(As I remember it) A couple years back a guy rented an Arrow out of
Bay City. He took a friend and the friend's son for a ride. They did
a wee bit too much low flying looking at the farm land near his
friend's place as I understand it. They discovered a power line
ahead. He pulled up and started a turn. The left wing hit the ground
wire that runs along the top of the line. It stretched that heavy
line out and broke it. The line whipped around and ended up winding
itself around the hot wires shutting down power for several square
miles. (3 survivors)

The Arrow? Well, after missing the ground by inches, while probably
trying to imitate a Frisbee (TM), they headed back to Bay City.
Parked the plane, took his friend's son home and headed for a bar.
Even though ill advised I can truely understand their desire for a
drink at the time (and the removal of the seat cushions.)

One of the guys at Bay City (3CM) noticed the Arrow looked kinda
different setting out there on the ramp. At first he thought they had
just forgotten to put the flaps up so he got in to put the flaps up,
but they wouldn't move. Then he got out to look at the plane. The
wings were actually skewed to the left and by quite a bit. I believe
there was something like a 3 to 4 inch gap between the leading edge
and the fuselage on the pilot's side. The wing was torqued so bad
they couldn't get the flaps back up.

Unfortunately the renter had neglected to mention he had encountered a
any difficulties on the flight.

The police found him and his friend at the bar.

So the total was 4 airplanes with three of the four killing all on
board. OTOH there were 3 survivors out of 7.

As I understand they actually rebuilt the Arrow and it's still flying.
The kicker though: They had sold the Arrow and the new owner was to
pick it up the next morning. Needless to say they had to call him and
ask for a delay. (I don't remember if he actually ended up buying the
plane after that or not. Seems like he did)

I can see it now: "Oh, BTW, before we go out we have discovered some
minor problems we need to take care of before you take it home."

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

On Fri, 07 Jan 2005 12:18:21 GMT, wrote:



Like I said,

If youcan see the runway, there ain't no hill between you and it

Depends on your rate of descent. That runway can disappear pretty
fast.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com