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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.
IFR CRUISING ALTITUDE OR FLIGHT LEVEL
In controlled airspace, pilots must maintain the altitude
or flight level assigned by ATC, although if the ATC
clearance assigns “VFR conditions on-top,” an altitude
or flight level as prescribed by Part 91.159 must be
maintained. In uncontrolled airspace (except while in a
holding pattern of 2 minutes or less or while turning) if
operating an aircraft under IFR in level cruising flight,
an appropriate altitude as depicted in the legend of
NACO IFR en route high and low altitude charts must
be maintained. [Figure 3-21]
When operating on an IFR flight plan below 18,000 feet
MSL in accordance with a VFR-on-top clearance, any
VFR cruising altitude appropriate to the direction of
flight between the MEA and 18,000 feet MSL may be
selected that allows the flight to remain in VFR conditions. Any change in altitude must be
reported to ATC and pilots must comply
with all other IFR reporting procedures.
VFR-on-top is not authorized in Class A
airspace. When cruising below 18,000
feet MSL, the altimeter must be adjusted
to the current setting, as reported by a
station within 100 NM of your position.
In areas where weather-reporting stations are more than 100 NM from the
route, the altimeter setting of a station
that is closest may be used. During IFR
flight, ATC advises flights periodically
of the current altimeter setting, but it
　
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