FN FAL
Freight Dawgs Rule
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Poorly thought out? What are you turning Democrat on us?100LL... Again! said:With GPS becoming more prevalent, I am betting that the 22nm reg will go away at some point for /G filers. Not to mention that ATC can clear you to whatever altitude their chart shows for your area. If ATC clears me there and it does not conflict with the OROCA or MORA (Jepp), then I feel just fine going there.
If the MOCA is safe within 22nm, it's safe along the whole route.
It is VERY IMPORTANT to remember that the regs are a very poorly thought out set of rules. There are many cases that can be posited that have no good answer in the regs. That is where the responsibility and authority of the PIC comes in.
MOCA is for Republicans, MEA is for Democrats. They raised the mins for the liberals so those pootietangs have an excuse to stay at home with their same sex lovers.
Avweb says it's true...so it must be. At least I can cite a reference. All the rest have been talking out the toothless wonder.
continued...All Those Ms
May 8, 1996
By Bill English,
This originally appeared in the November 1994 issue of IFR MAGAZINE and appears by permission of Belvoir Publications.
The FAA's TERPS wizards chart MEAs, MOCAs, MCAs and MRAs to make sure we can fly through the clag without encountering embedded rocks and trees. Sometimes we have to fly at or above these minimum altitudes, but not always. Here's the skinny.
During a typical IFR flight, you probably make lots of decisions without much forethought. One of them is the altitude to file and fly. Unless there's ice around or known rocks in the clouds or an intense head or tailwind, what difference does it make?
All you have to do is look at the published MEAs and be sure you're above them, right? And besides, you'd never get a clearance that could be below those MEAs, right? Yeah, well as someone famous once said "Trust, but verify." Sometimes what appears to be a simple truth is not what it seems, especially when it comes to altitudes.
Let's dig around MEAs and their cousins on the en route chart and review some things that you may not have thought about in a while.
Building an Airway
MEAs and MOCAs are the meat and potatoes of the en route chart as far as obstacle clearance is concerned; knowing the underlying structure can serve you well. The airways are themselves regulations, FAR 95 and the 8260.3 (TERPS) manual govern the establishment and publication of the routes.
The required obstruction clearance is basically the same as described in FAR 91.177, requiring 1000 feet of obstacle clearance in non-mountainous terrain and 2000 feet in designated mountainous areas. The reason for the extra clearance over mountains is not to give you a nice cushion over rough (read remote) areas in case of an emergency, but mainly because of the Bernoulli effect as air flows over the mountains. The huge venturi created as the upper winds are forced over the terrain can cause large variations in the pressure gradient at given true altitudes, resulting in large altimeter errors.
In certain mountainous areas, that 2000-foot minimum may be reduced. A 1500-foot clearance is allowed in the mountainous areas of the Eastern U.S., Puerto Rico and Hawaii. In the Western U.S. and Alaska, the clearance may be reduced to 1700 feet. When designating these areas, the specialists must take a careful look at the geography. TERPS requires them to consider areas of precipitous terrain, weather phenomena peculiar to the area and any conditions conducive to marked pressure differentials, such as canyons, which can act like giant venturis.
Other considerations are the type of navaids used and the distance between them and the availability of weather and altimeter information in the area. The width of the airway for both non-radar separation and obstruction-clearance purposes is 4 nautical miles either side of the centerline out to 50 nautical miles from the VOR defining the route. If the airway segment extends more than 50 miles, the protected airspace fans out 4.5 degrees from the centerline.
If you could see the protected area of an airway and could slice out a section of it, you'd be left with the trapezoidal shaped section shown. The airway has a "primary" obstacle clearance area that extends 4 miles either side of the centerline. A secondary, or buffer zone extends an additional 2 miles either side of the airway and angles up to intersect the airway's extreme outer edge, as shown schematically in the drawing. So, you can see that even if you're a mile or two off the centerline, there's plenty of obstacle clearance.
The width of the airway and/or secondary protected airspace is expanded at points where the airway turns over a navaid or intersection. The amount of extra protection depends on how sharp the turn is, the MSL altitude of the area to be protected (due to the higher true speeds), and the distance from the appropriate navaids.The TERPS nerds have formulas to calculate all of this; you don't need to worry about it.
On to the MEA
So once all this is done, we have an MEA right? No, not really, we just have a MOCA or minimum obstacle clearance altitude. That altitude is set by the highest or "controlling" obstacle (terrain or man-made) that comes within 1000 feet of the bottom of the airway's primary clearance area. Fly at the MOCA and you're guaranteed obstacle clearance but reception of navaids is only promised within 22 nautical miles of the stations.
The MEA, on the other hand, guarantees obstruction clearance and navaid reception along its entire length, unless there's an MEA gap, which will be indicated on the chart. That's a rather taller order than just 1000 feet of clearance so most MEAs really provide a lot more than the minimum required clearance. They're higher primarily to assure navigation reception of the VORs that anchor both ends of the route.
The flight inspection folks will tell you that radio communication is also checked and is supposed to be available along the entire route but you probably know from experience that this isn't always true. Centers and tracons have transceiver sites scattered all over the place and some work better than others.
The Flight Check guys fly the airway and make sure that what looks good on paper actually "plays" along the entire proposed route. If it doesn't work, they'll jack up the MEA until it does. In certain mountainous areas, airways are established beyond usable navaid limits and a gap is shown on the chart where dead-reckoning or some other form of navigation is needed.
The gap can't be larger than a specified size, depending on the altitude of the MEAs leading to the gap. If it's larger, up goes the MEA until it shrinks or the airway is moved somewhere else.
Even when no gap exists, there are problems. The VOR system being what it is_that is, crumbling a bit at the edges_flight inspectors sometimes have to be resourceful about making an airway work without resorting to a stratospheric MEA. The notorious Harrisburg VOR took years of work to support enough airways to earn its keep. It's still a highly restricted navaid.
You probably know that VORs have standard service volumes of 40 miles for L-class and H-class below 14,500 feet and 25 miles for T-class. Very often, though, a T-class will be pressed into service to make an airway play beyond the 25-mile limit. A good example of a VOR with "expanded service volume" is Bradley (BDL) Connecticut.