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range. Sectors provide separation from terrain and
obstructions. Each MVA chart has sectors large
enough to accommodate vectoring of aircraft within
the sector at the MVA. [Figure 3-17 on page 3-14]
MINIMUM RECEPTION ALTITUDE
Minimum reception altitudes (MRAs) are determined by FAA flight inspection traversing an entire
route of flight to establish the minimum altitude the
navigation signal can be received for the route and
for off-course NAVAID facilities that determine a fix.
When the MRA at the fix is higher than the MEA, an
MRA is established for the fix, and is the lowest altitude at which an intersection can be determined.
MINIMUM CROSSING ALTITUDE
A minimum crossing altitude (MCA) is the lowest altitude at certain fixes at which the aircraft must cross when
proceeding in the direction of a higher minimum en route
IFR altitude, as depicted in Figure 3-18 on page 3-14.
MCAs are established in all cases where obstacles intervene to prevent pilots from maintaining obstacle clearance
during a normal climb to a higher MEA after passing a
point beyond which the higher MEA applies. The same
protected en route area vertical obstacle clearance requirements for the primary and secondary areas are considered
in the determination of the MCA. The standard for determining the MCA is based upon the following climb
gradients, and is computed from the flight altitude:
• Sea level through 5,000 feet MSL—150 feet per
NM
3-14
Figure 3-17. Example of an Air Route Traffic Control Center MVA Chart.
10,000
RIW
15,800
14,500
12,000
13,700
10,700
11,000
12,400
12,000
15,500
14,200
11,000
13,800
13,300
12,300
CKW
VEL
FBR
RKS
RKS 325
RKS 003
070
065
243
142
RKS 269
211
RKS 080
270
001
065
110
180
RKS 160
20
40
60
80
100
120
14,500
0 00
70
00 0
2, 2, 00
14
5
C
00 0
X
V 361
5900
V 361
5200
V 361 5900 E
SQWID
Figure 3-18. Minimum Crossing Altitude.
3-15
• 5000 feet through 10,000 feet MSL — 120 feet
per NM
• 10,000 feet MSL and over — 100 feet per NM
To determine the MCA seen on a NACO en route
chart, the distance from the obstacle to the fix is computed from the point where the centerline of the en
route course in the direction of flight intersects the
farthest displacement from the fix, as shown in Figure
3-19. When a change of altitude is involved with a
course change, course guidance must be provided if
the change of altitude is more than 1,500 feet and/or if
the course change is more than 45 degrees, although
there is an exception to this rule. In some cases, course
changes of up to 90 degrees may be approved without
course guidance provided that no obstacles penetrate
the established MEA requirement of the previous airway or route segment. Outside U. S. airspace, pilots
may encounter different flight procedures regarding
MCA and transitioning from one MEA to a higher
MEA. In this case, pilots are expected to be at the higher
MEA crossing the fix, similar to an MCA. Pilots must
thoroughly review flight procedure differences when flying outside U.S. airspace. On NACO en route charts,
routes and associated data outside the conterminous U.S.
are shown for transitional purposes only and are not part
of the high altitude jet route and RNAV route systems.
[Figure 3-20]
Figure 3-19. MCA Determination Point.
3200'
700'
2000'
2000'
6 NM
4620' MSL
120' per NM Required
Multiply by 6 NM -720 Ft.
Maximum Displacement
MSL
Obstacle Line
Obstruction Height 4620'
Required Clearance +2000'
MOCA At Obstruction = 6620'
Climb Value* - 720'
MCA Required = 5900'
* Based upon 6 NM @ 120 Feet Per NM
X
MEA 5200'
MCA 5900' E
Figure 3-20. Crossing a Fix to a Higher MEA in Canada.
3-16
MAXIMUM AUTHORIZED ALTITUDE
A maximum authorized altitude (MAA) is a published
altitude representing the maximum usable altitude or
flight level for an airspace structure or route segment. It
is the highest altitude on a Federal airway, jet route,
RNAV low or high route, or other direct route for which
an MEA is designated at which adequate reception of
navigation signals is assured. MAAs represent procedural limits determined by technical limitations or other
factors such as limited airspace or frequency interference of ground based facilities.
　
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