Minimum Safe Altitude (MSA) Standards

MSA is defined in the AIM as "altitudes depicted on approach charts
which provide at least 1,000 feet of obstacle clearance." So, if an MSA
is 3000 ft, does that necesarily mean that there is at least one
obstacle in the area that is 2000 ft tall or could there be some other
reason for the 3000 ft setting? If there are only one or two towers in
the north part of the MSA circle and the rest of the area is completely
flat at 1000 ft (MSL), then would they always break the sector into
pieces are create a sector at 2000 ft, and just put the northern half at
3000 ft, or is that too much trouble in general?

While I am at it, is there any easy way to find the obstacle in a quad
of VFR sectional that makes the quad's Maximum Elevation Feature (MEF)
at the level that is at. It is a bit of a pain to search the quad's
entire area to find that one tower that makes the MEF way above the
surrounding terrain. It seems that they could mark the highest feature
in some distinctive way. OK, so maybe I am lazy.


-Sami (N2057M, Piper Turbo Arrow III)

In article ,
"O. Sami Saydjari" wrote:

MSA is defined in the AIM as "altitudes depicted on approach charts
which provide at least 1,000 feet of obstacle clearance." So, if an MSA
is 3000 ft, does that necesarily mean that there is at least one
obstacle in the area that is 2000 ft tall or could there be some other
reason for the 3000 ft setting? If there are only one or two towers in
the north part of the MSA circle and the rest of the area is completely
flat at 1000 ft (MSL), then would they always break the sector into
pieces are create a sector at 2000 ft, and just put the northern half at
3000 ft, or is that too much trouble in general?

There are rules on how many different sectors you can have, how big they
must be, etc. I don't remember the details, but you should be able to
find them in TERPS.

While I am at it, is there any easy way to find the obstacle in a quad
of VFR sectional that makes the quad's Maximum Elevation Feature (MEF)
at the level that is at. It is a bit of a pain to search the quad's
entire area to find that one tower that makes the MEF way above the
surrounding terrain. It seems that they could mark the highest feature
in some distinctive way. OK, so maybe I am lazy.

I don't know of any way other than exhaustive search.

MSA is defined in the AIM as "altitudes depicted on approach charts
which provide at least 1,000 feet of obstacle clearance." So, if an MSA
is 3000 ft, does that necesarily mean that there is at least one
obstacle in the area that is 2000 ft tall or could there be some other
reason for the 3000 ft setting?


"at least" means "no less than, but maybe more than, though maybe not". So, it
does not necessarily mean that there is at least one obstacle 2000 ft tall. I
don't know the actual criteria for designing these things, but wherever there
is wiggle room, expect something to wiggle and you'll be safe.


While I am at it, is there any easy way to find the obstacle in a quad
of VFR sectional that makes the quad's Maximum Elevation Feature (MEF)
at the level that is at. It is a bit of a pain to search the quad's
entire area to find that one tower


Nope. And even if you found that one tower, you are still left with that other
tower that is two feet lower, but in a different area. And the hill that
doesn't have a tower, but it tall enough by itself to qualify as the third
highest elevation (by only fourteen feet), so only has a dot.

Besides, not all towers are indicated on the chart. They say so explicitly.

You'll need to study the sectional anyway to check for parachute areas, MOAs,
ATAs, landmarks, wires, frequencies, and all sorts of other things relevant to
VFR flight and even IFR flight for that matter, especially if you are going to
graze the trees, as I like to (for the view).

Jose



--
(for Email, make the obvious changes in my address)

There are rules on how many different sectors you can have, how big they
must be, etc. I don't remember the details, but you should be able to
find them in TERPS.


I am sorry to demonstrate my ignorance, but what are the "TERPS" and
where might I find them? I did notice that the AIM says that sectors
have to be no smaller than 90 degrees, so there can be no more than
four. It does not say the criteria for deciding when and whether to
subdivide the MSA circle.

-Sami

In article ,
wrote:

I am sorry to demonstrate my ignorance, but what are the "TERPS"

The United States Standards for Terminal Instrument Procedures.
iow, the FAA rules for creating airways, routes, and approaches.

and where might I find them?

I don't have a link handy, but you can search www.faa.gov. Note
that you can't find all of the FAA regs/orders for the TERPS in one
document or one place, the main document likely be all that you'd
want to see.

--
Bob Noel

"Bob Noel" wrote in message
...

... what are the "TERPS"

I don't have a link handy, but you can search www.faa.gov. Note
that you can't find all of the FAA regs/orders for the TERPS in one
document or one place, the main document likely be all that you'd
want to see.

http://av-info.faa.gov/terps/directives%20page.htm

now has virtually everything, I think. Beware file size though, 8260.3B is
about 30 MB.

Julian Scarfe

In article ,
"O. Sami Saydjari" wrote:


There are rules on how many different sectors you can have, how big they
must be, etc. I don't remember the details, but you should be able to
find them in TERPS.


I am sorry to demonstrate my ignorance, but what are the "TERPS" and
where might I find them? I did notice that the AIM says that sectors
have to be no smaller than 90 degrees, so there can be no more than
four. It does not say the criteria for deciding when and whether to
subdivide the MSA circle.

-Sami


TERPS is "United States for Terminal Instrument Procedures". You can
find a copy here....

http://av-info.faa.gov/terps/directives%20page.htm

It describes in gruesome detail what goes into constructing IFR
procedures such as instrument approaches.

The context of minimum sector altitudes is important...they are to be used
only in emergencies. I see many postings in which a pilot is trying to fit
an MSA into an approach procedure.

Bob Gardner

"O. Sami Saydjari" wrote in message
...
MSA is defined in the AIM as "altitudes depicted on approach charts
which provide at least 1,000 feet of obstacle clearance." So, if an MSA
is 3000 ft, does that necesarily mean that there is at least one
obstacle in the area that is 2000 ft tall or could there be some other
reason for the 3000 ft setting? If there are only one or two towers in
the north part of the MSA circle and the rest of the area is completely
flat at 1000 ft (MSL), then would they always break the sector into
pieces are create a sector at 2000 ft, and just put the northern half at
3000 ft, or is that too much trouble in general?

While I am at it, is there any easy way to find the obstacle in a quad
of VFR sectional that makes the quad's Maximum Elevation Feature (MEF)
at the level that is at. It is a bit of a pain to search the quad's
entire area to find that one tower that makes the MEF way above the
surrounding terrain. It seems that they could mark the highest feature
in some distinctive way. OK, so maybe I am lazy.


-Sami (N2057M, Piper Turbo Arrow III)

I realize that that is what the AIM says, but why are they to be used
for emergencies only? I always interpreted the MSA as the minimum
altitude to use when flying off-feeder routes (direct to the IAF),
sort of like the OROCA when flying off-airways.





"Bob Gardner" wrote in message news:EJJ2c.135940$4o.172500@attbi_s52...
The context of minimum sector altitudes is important...they are to be used
only in emergencies. I see many postings in which a pilot is trying to fit
an MSA into an approach procedure.

Bob Gardner

"O. Sami Saydjari" wrote:


I am sorry to demonstrate my ignorance, but what are the "TERPS" and
where might I find them? I did notice that the AIM says that sectors
have to be no smaller than 90 degrees, so there can be no more than
four. It does not say the criteria for deciding when and whether to
subdivide the MSA circle.

In the case of RNAV approaches, there is only one MSA. It is not very useful
information, nor has it ever been.