A normal IDP requires 152 ft/nm, about 350 ft. min @ 120
KIAS.
Many airports have obstacles that require a steeper climb,
so they publish "non-standard TO minima"
Some airports cannot be departed safely in IMC due to local
terrain.
Altitudes required to clear an obstruction include a margin,
2,000 feet in mountainous regions and 1,000 feet in other
areas.
The IDP gradient at Aspen is based on the angle from the
departure end to the critical obstacle, a rate that is well
above the engine-out performance of most airplanes. [460
ft/nm will be close to 1,000 ft/min and most turboprops
won't do that on one engine, it is the worst your plane can
do that is the performance you need to consider.]
Once past the critical obstacle, a climb at standard rates
will be safe. [Again, those rates may be above the
performance of many smaller, low powered aircraft.]

The ideal airplane for Aspen is probably an F15-F22 class
fighter, go vertical to FL 240. But most pilots don't fly
with that much power.

Aspen is a dangerous place for the unprepared and a
wonderful place for those who know how to fly in the
mountains, when to fly and have the equipment and stay
within the limits.


wrote in message
oups.com...
I have a question about the ceiling and visibility minima as
alternates for climb gradients in departure procedures. A
good
example is at Aspen (KASE), straight out of the FAA
Instrument
Procedures Handbook, but they don't explain the portion I
find
difficult to understand. I've duplicated the entire text of
the
procedure at the bottom of this message.

So the issue I have is that the required ceiling to avoid
the 460 ft/
nm gradient is 3100 feet. That makes an MSL altitude of
just under
11,000 feet as the minimum for the bases of the clouds.
But, if the
clouds are lower, the 460 ft/nm gradient is to be maintained
all the
way to 14,000 feet MSL.

So are all the obstacles below the 11,000 foot ceiling, or
not? If
not, how can the 3100-3 minimums with standard climb
gradient result
in a safe operation? Conversely, if all the obstacles
penetrating the
40:1 surface are indeed below 11,000 feet, then why require
the 460 ft/
nm gradient all the way to 14000 feet? I understand that
there will
be some obstacle clearance provided by the gradient, whereas
the
ceiling can be right on the obstacle, but 3000 feet of
difference
between the two seems too much for that explanation.

The old TERPS (in paragraph 1208) stated that "The ceiling
value shall
be the 100-foot increment above the controlling obstacle or
above the
altitude required over a specified point from which a 40:1
gradient
will clear the obstacle." What does the second part, after
the "or,"
mean? And does that have anything to do with the Aspen
procedure? I
believe that the newest revision of the TERPS has deleted
that second
part and added the description of a
visual-climb-over-the-airport
procedure. Is that supposed to be a replacement with
different
terminology, or are those two things not related?

ASPEN-PITKIN COUNTY/SARDY FIELD
TAKE-OFF MINIMUMS: Rwy 15, NA. Rwy 33, 3100-3
or 1000-2 with a min. climb of 460' per NM to 14000.
DEPARTURE PROCEDU Climb heading 340° to
8700, then climbing left turn to 16000 heading 270° to
intercept and proceed via I-PKN northwest course
outbound on backcourse and DBL R-244 outbound to
GLENO Int/DBL 22.7 DME. Climb in GLENO holding
pattern (SW, left turns, 064° inbound) to cross GLENO
at 16000 before proceeding in route.
NOTE: Rwy 33, 8179' tree 3447' from departure end of
runway, 1379' left of centerline.

The IPH also has an example of the
visual-climb-over-the-airport
procedure, which is very explicitly stated as part of the
ODP:
BECKWOURTH, CA
NERVINO
TAKE-OFF MINIMUMS: Rwys 7, 25, 3500-3 for climb in
visual conditions.
DEPARTURE PROCEDU Rwys 7, 25, for climb in
visual conditions: cross Nervino Airport at or above
8300 before proceeding on course.

thanks,

Peter