PDX airspace …

[OR75]

can anyone help me understand this peculiar class C boundary ? 
GPS precision challenge ? 
Or Maybe just to keep Portland weird ?
 

[philip_g]

Excluding the river from the sfc up area so float planes can get in and out is my best guess.

Edited March 30, 2022 by philip_g

[ArtVandelay]

Garmin’s dynamic maps don’t show that:

[philip_g]

  On 3/30/2022 at 6:46 AM, ArtVandelay said:

Garmin’s dynamic maps don’t show that:

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Skyvector does and that's taken from the scanned sectional charts.

[N201MKTurbo]

It looks like it just follows the shoreline in that area instead of the DME arc. The shoreline follows the Swan Basin inlet. It doesn’t look useful for anything aviation related.

There are a few helicopter ships in dry dock there. Maybe it is there to allow helicopters to fly to and from the ships without calling approach?

[Greg Ellis]

If you look at a satellite view of this area, that projected area of Class C is right over top of a very heavy industrial area.  There is also the US Coast Guard station Portland there and I wonder if it has anything to do with either one of those things.  The little water inlet is called the Swan Island Basin.

[jaylw314]

That area looks like this.  Note the peninsula that corresponds to the "finger"in the class C.

The reason it's that way is that the class C surface area there is anything not over the water.  If it's over the water (or southwest), you're in the shelf area.  It makes sense since the people flying under the shelf are VFR pilots only, and there's a threatening ridge that runs southwest of the river with radio towers up to 2,000 MSL, so you need some sort of unambiguous visual reference for people to navigate the narrow passage under the shelf without running afoul of the surface area.

Pearson airport (VUO) is also a popular airfield that's interesting in that it is the only nontowered class D airspace in the country, just to the west of PDX.  Given the ridge and the busy Hillsboro class D just to the west, VFR pilots have a narrow, well-defined route into Pearson, sight-seeing over Portland, or transitioning N/S under PDX.

It's a little clearer on the PDX sectional inset map:

Edited March 30, 2022 by jaylw314

[jaylw314]

  On 3/30/2022 at 5:26 PM, Greg Ellis said:

If you look at a satellite view of this area, that projected area of Class C is right over top of a very heavy industrial area.  There is also the US Coast Guard station Portland there and I wonder if it has anything to do with either one of those things.  The little water inlet is called the Swan Island Basin.

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Probably not, it doesn't look like they keep any helos there?  It's probably more to keep in line with the implied rule that everything over the Willamette River (and to the south and west) is under the shelf, and everything over the Columbia is controlled to the surface, until they meet at their confluence

Edited March 30, 2022 by jaylw314

[PT20J]

Pearson Airpark actually has a FAR Part 93 Special Airport Traffic Area denoted by the blue crosshatch. Part 93 was originally developed for Anchorage AK to define rules to separate aircraft using the close proximity Anchorage International, Lake Hood seaplane base, Lake Hood airstrip, Merrill Field and Elmendorf AFB in the days before Class B, C and TRSA airspaces existed. Since then, a number of other airports have been included in Part 93 as the need arose. 

Having grown up in Portland, I found the Swan Island "wrinkle" in the inner circle interesting. Swan Island was originally the Portland airport until it turned into a shipyard during the Second World War. It is now an industrial area. For fun, I called the PDX TRACON and inquired about it. Apparently that wrinkle has been there since the Charlie airspace was defined. No one remembers why. Speculation is that it may have had to do with helicopter traffic in the past. It seems to be no longer operationally relevant, but it is so hard to change airspace (NPRMs and such) that there has been no impetus to change it.

Skip

[carusoam]

Some wrinkles have been known to cause challenges…

You can fly in, but your plane may not be able to fly a 180° U turn at the end…

The east side of Manhattan was a virtual blocked canyon… aka the East River…

Virtual because the canyon walls are imaginary…

After losing a famous pilot/ball player… a route across Manhattan was approved…

1) Going slow is a nice way to minimize the turn radius…

2) Using steep turns can also minimize the turn radius…

3) Combining the two methods is a way to demonstrate accelerated stalls… without any room for recovery…

 

So… use caution flying into funky old wrinkles on VFR charts…. They may be best for helicopter traffic…

 

PP thoughts only, not a CFI…

-a-

[rbp]

  On 4/1/2022 at 3:49 AM, carusoam said:

 

After losing a famous pilot/ball player… a route across Manhattan was approved…

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there is no Bravo Exclusion Zone route across manhattan.
the Central Park route is a heli-only route and requires a clearance. 

[jaylw314]

  On 4/1/2022 at 3:37 AM, PT20J said:

Pearson Airpark actually has a FAR Part 93 Special Airport Traffic Area denoted by the blue crosshatch. Part 93 was originally developed for Anchorage AK to define rules to separate aircraft using the close proximity Anchorage International, Lake Hood seaplane base, Lake Hood airstrip, Merrill Field and Elmendorf AFB in the days before Class B, C and TRSA airspaces existed. Since then, a number of other airports have been included in Part 93 as the need arose. 

Having grown up in Portland, I found the Swan Island "wrinkle" in the inner circle interesting. Swan Island was originally the Portland airport until it turned into a shipyard during the Second World War. It is now an industrial area. For fun, I called the PDX TRACON and inquired about it. Apparently that wrinkle has been there since the Charlie airspace was defined. No one remembers why. Speculation is that it may have had to do with helicopter traffic in the past. It seems to be no longer operationally relevant, but it is so hard to change airspace (NPRMs and such) that there has been no impetus to change it.

Skip

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That's pretty funny about asking TRACON  

[PT20J]

OK, I figured this out. The textual descriptions of airspace classes are contained in JO 7400.11. The description of the class C in the vicinity of Swan Is is "excluding that
airspace west of the east bank of the Willamette River". Swan Is, originally an island but later connected to the east shore of the river by landfill, is thus a peninsula and so it is part of the east shore. The "wrinkle" in the depiction is merely a consequence of following the shoreline as defined in the textual description.

Skip

JO_Order_7400.11F_508.pdfFetching info...

[carusoam]

  On 4/1/2022 at 6:26 PM, rbp said:

there is no Bravo Exclusion Zone route across manhattan.
the Central Park route is a heli-only route and requires a clearance. 

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Pretty much keeps the East River… airplane unfriendly doesn’t it?  

PIC still has to use some good planning skill to not get trapped…

Best regards,

-a-

[rbp]

  On 4/1/2022 at 9:34 PM, carusoam said:

Pretty much keeps the East River… airplane unfriendly doesn’t it?  

PIC still has to use some good planning skill to not get trapped…

Best regards,

-a-

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Immelman