David Young
Technical Subject Areas
1. Subject – Enroute and Lost Communications Procedures.
2. Introduction – Although most people think of instrument flying as shooting approaches
down to minimums, most of instrument flying is done during the enroute phase of flight.
Flying IFR is much different than VFR, and it is essential to understand what those
differences are, how to fly IFR enroute, and what to do in case of a lost communications
situation (often termed lost comms).
3. Outline –
a. Discuss victor airways.
b. Define the minimum altitude terms.
c. Chart symbols.
d. Required reports.
i. Required at all times.
ii. In non-radar environments.
iii. Position reports.
e. IFR cruising altitudes.
f. Types of IFR altitude clearances.
g. VFR-on-top.
h. Clearance limit.
i. Review lost communications procedures.
i. AVEF.
ii. MEA.
iii. EFC/ETA.
4. Contents –
a. In IFR flying, there exists “roads” in the sky (called victor airways) that are used
to help us get from one point to another.
i. Since we cannot rely on dead reckoning or pilotage, we must use more
accurate methods which rely on instruments.
ii. Typically, victor airways are formed by radials coming off VORs which
lead to other radials coming off other VORs.
iii. Victor airways are a total of 8nm wide (4nm on each side of center).
iv. In conjunction with a federal airway, class E airspace goes down to 1,200
ft AGL.
v. Many times there are defined points, or fixes, along these airways that are
used to aid the pilot in navigation.
1. Sometimes these fixes are defined by DME distances and other
times by VOR cross-radials.
2. These fixes might exist where an airway bends or where multiple
airways intersect.
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3. Each fix is assigned a name i.e. LODGE or SIMMN (pronounced
“Sy-mun”).
a. When these fixes are not English words, it is best to just try
and pronounce them the way they are written.
b. There are many terms designated to differentiate types of altitude. These include
MEA, MOCA, OROCA, MCA, MRA, MSA, and MAA.
i. On a side note, a minimum obstacle clearance altitude in non-mountainous
terrain is 1,000 ft above the highest point and 2,000 ft above the highest
point in mountainous terrain.
1. Check the AIM for a depiction of “mountainous terrain.”
ii. MEA (Minimum Enroute Altitude) – The lowest published altitude
between radio fixes which assures acceptable navigational signal coverage
and meets obstacle clearance requirements between those fixes.
1. It applies to the entire width of any federal airway.
2. Usually designated as a number along an airway in enroute charts.
iii. MOCA (Minimum Obstruction Clearance Altitude) – The lowest
published altitude between two radio fixes on VOR airways which assures
acceptable navigational signal coverage within 22 nm of the fixes and
meets the obstacle clearance requirements between those fixes.
1. Usually designated as a * followed by a number for NACO charts.
a. E.g. *3500.
2. For Jeppesen charts, it is usually a brownish number followed by a
“T”.
a. E.g. 3500T.
iv. OROCA (Off-Route Obstacle Clearance Altitude) – The highest possible
elevation, including terrain and other vertical obstructions, bounded by the
ticked lines of latitude and longitude.
1. OROCAs are usually depicted as follows: 125, which means the
OROCA for that quadrangle is 12,500 ft.
v. MCA (Minimum Crossing Altitude) – The lowest altitude at certain radio
fixes at which an aircraft must cross when proceeding in the direction of a
higher minimum enroute altitude.
1. The MCA should be reached BEFORE reaching the fix it is
defined for.
2. Refer to Figure A for a depiction of an MCA on NACO charts.
3. For Jeppesen charts, it is usually designated as something like
“V64 12000S,” which means the MCA for V64 southbound is
12,000 ft MSL.
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vi. MRA (Minimum Reception Altitude) – The lowest published altitude
between radio fixes which assures acceptable navigational signal
coverage.
1. It does not assure terrain coverage.
2. Refer to Figure B for a depiction of an MRA on NACO charts.
vii. MSA (Minimum Sector Altitude) – The lowest published altitude within
25 nm of a fix that meets obstacle clearance requirements.
viii. MAA (Maximum Authorized Altitude) – The highest published altitude
usable for a route segment that ensures signal reception without
interference from another signal on the same frequency.
c. There are many symbols that are unique to IFR enroute charts.
i. Changeover Point (refer to Figure C) – the point on an airway where you
should switch to another navaid for navigation purposes.
ii. Change in MEA/MOCA (refer to Figure D).
iii. Compulsory Reporting Points (refer to Figure E).
iv. Non-Compulsory Reporting Points (refer to Figure F).
d. Regulations state that in certain situations, a pilot must make position reports.
i. The following should be made at all times without a specific request:
1. When vacating any previously assigned altitude or flight level for a
newly assigned altitude or flight level.
2. When an altitude change will be made if operating on a clearance
specifying VFR-on-top.
3. When unable to climb/descend at a rate of at least 500 fpm.
4. When going missed off an approach.
5. Change in TAS when it varies by 5% or 10 kts, whichever is
greater, from that filed in the flight plan.
6. The time and altitude or flight level upon reaching a holding fix or
point that the pilot is cleared to.
7. When leaving any assigned holding fix or point.
8. Any loss, in controlled airspace, of VOR, ADF, complete or partial
loss of ILS receiver capability or impairment of air/ground
communications capability.
9. Any information relating to the safety of flight.
10. Upon encountering any weather or hazardous conditions not
forecasted.
ii. The following should be made at all times when not in radar contact:
1. When leaving the FAF inbound (non-precision approach) or when
leaving the outer marker (or fix used in lieu of the outer marker)
inbound (precision approach).
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2. A corrected estimate at anytime it becomes apparent that a
previous estimate is in error in excess of 3 minutes.
iii. A position report should be made in the following format:
1. Identification.
2. Position.
3. Time.
4. Altitude/flight level.
5. ETA and name of next reporting point.
6. The name of the next succeeding reporting point along the route.
7. Remarks.
e. When cruising on an IFR flight plan, much like a VFR flight plan, you must fly at
specific altitudes.
i. When flying a MAGNETIC COURSE of 360º - 179º, you are to fly at an
odd altitude above the MEA.
ii. When flying a MAGNETIC COURSE of 180º - 359º, you are to fly at an
even altitude above the MEA.
f. In IFR flying, there are two types of altitude clearances – maintain and cruise.
i. Maintain – Self-explanatory. Maintain the altitude you were assigned.
ii. Cruise – You may fly any altitude between the MEA and the altitude
given.
1. This is used to give the pilot a block of altitude to work with to
avoid hazardous weather/turbulence.
2. The pilot may level off at an intermediate altitude and
climb/descend at the pilot’s discretion.
a. However, once the pilot starts a descent and VERBALLY
reports leaving an altitude in the block, he/she may not
return to that altitude without additional ATC clearance.
g. A VFR-on-top clearance is an IFR clearance that allows a pilot to fly at any VFR
altitude in visual conditions above the clouds.
i. This is useful if you would like to climb through a cloud/haze layer and
cancel your IFR clearance once on top.
ii. Altitudes must adhere to VFR, not IFR, regulations.
iii. Cloud separation criteria must be maintained.
iv. You are still operating under an IFR clearance (unless you cancel IFR), so
those regulations also apply, but not with altitude.
1. This includes minimum IFR altitudes, position reporting, radio
communications, course to be flown, adherence to ATC
clearances, etc.
v. VFR-on-top is prohibited in class A airspace.
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h. Most of the time when you fly, you are cleared to your destination airport.
However, it is possible to only be cleared so far as a clearance limit that is not
your destination airport.
i. When issued a clearance limit, you are always given an Expect Further
Clearance (EFC) time.
1. If no EFC time is given, request one from ATC as it is important in
a lost communications scenario.
i. One of the most important parts of instrument training is what to do in case you
lose radio communications.
i. Usually, ATC will tell you what to do and when.
1. You can see why losing contact with them would be a big deal.
ii. This is why the FAA has written procedures dealing with this sort of
scenario.
iii. In case you lose radios, the route you fly to your destination or clearance
limit is (in this order) –
1. Assigned.
2. Vectored.
3. Expected.
4. Filed.
iv. In case you lose radios, the altitude you at is the HIGHEST of the
following along that route of flight –
1. Minimum IFR altitude.
2. Expected.
3. Assigned.
v. If the clearance limit is a fix from which the approach begins –
1. If given an EFC time a. Commence a descent or descent and approach as close as
possible to the EFC.
2. If not given an EFC time –
a. Commence a descent or descent and approach as close as
possible to the ETA as calculated on your flight plan or as
amended with ATC.
vi. If the clearance limit is not a fix from which the approach begins –
1. If given an EFC time –
a. Hold at the clearance limit until EFC, and then depart.
i. If you arrive at the limit at or past your EFC, then
continue on your route of flight using AVEF.
2. If not given an EFC time –
a. Depart the clearance limit and proceed to a fix from which
an approach begins and commence descent or descent and
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approach as close as possible to the estimated time of
arrival as calculated on your flight plan or as amended with
ATC.
5. Evaluation –
a. The student can explain what a victor airway is.
b. The student can explain the different types of minimum IFR altitudes.
c. The student can explain the different chart symbols.
d. The student can explain when position reports are necessary and how to make
them.
e. The student can explain what the IFR cruising altitudes are.
f. The student can explain what the difference between “cruise” and “maintain” is.
g. The student can explain VFR-on-top.
h. The student can explain what a clearance limit is.
i. The student can explain what to do in case of a lost communications situation.
6. References –
a. AIM 4-4-3.
b. AIM 5-3-2.
c. AIM 5-3-3.
d. §91.185.
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Figure A
Figure B
Figure C
Figure D
Figure E
Figure F