MAA, MRA, MCA, and OROCA: The Other IFR En Route Altitudes, Their Chart Flags, and When Each Actually Applies
Updated: 3 days ago
Instrument flying depends on more than maintaining assigned altitudes — it requires understanding why certain altitudes exist and when they apply. Beyond the MEA and MOCA that every instrument student learns first, IFR en route charts carry several other altitude definitions, each solving a different operational problem: one sets a ceiling rather than a floor, one applies only if you’re trying to identify a fix a particular way, one tells you to be climbing before you reach a fix rather than after, and one covers the airspace between the airways where no segment altitude exists. They’re flagged on the chart with small symbols that are easy to skim past — and each has a specific trigger that determines whether it affects you at all.
This post covers the four altitudes in practical depth: the MAA (and why it’s really about interference, not reception), the MRA (and the identification nuance that decides whether it applies), the MCA (and the 91.177 rule that governs it), and the OROCA (and how to read it on the grid) — plus the newer MTA and ATC’s own MVA/MIA for completeness, with chart depiction, a worked example for each, and the checkride questions.
Study this full length lesson (video, podcast, flashcards, and quiz) here: Full Length Lesson >
Where These Fit: The Full Altitude Family
A quick map before the detail, so each altitude has a place.
The segment altitudes (apply along an airway or route segment):
MEA — obstacle clearance + navigation signal, whole segment (the floor)
MOCA — obstacle clearance + VOR signal within 22 NM (a lower floor, conditionally)
MAA — the CEILING for the segment (this post)
The fix altitudes (apply at a specific point):
MRA — altitude to receive an off-route navaid to identify the fix (this post)
MCA — altitude you must be at when crossing the fix in a given direction (this post)
MTA — altitude for a turn at the fix at high altitude (this post)
The off-route altitude (applies where there’s no airway):
OROCA — grid-based obstacle clearance for direct and off-route flying (this post)
ATC’s altitudes (not published to pilots):
MVA / MIA — what ATC uses to vector and assign in their sectors
The one-line summary:
MEA/MOCA/MAA are about the segment; MRA/MCA/MTA are about the fix; OROCA is about everywhere else
Different triggers, different purposes
Know which one you’re under
(For MEA and MOCA in depth, see our MEA vs. MOCA post.)
MAA — Maximum Authorized Altitude
What it is:
The HIGHEST altitude at which adequate navigation signal reception is assured on a route segment — or, more broadly, the maximum usable altitude for that route structure
Unlike every other en route altitude, the MAA is a ceiling, not a floor
Published on Federal airways, jet routes, and RNAV routes
The upper limit of the route
The two sources of an MAA:
Structural: on most Victor airways, the common “MAA-17500” simply reflects the top of the low-altitude airway system, which ends at 17,999 feet. The airway doesn’t exist above that, so neither does its MAA
Interference: a lower MAA on a specific segment (say, MAA-11000) reflects a frequency-protection analysis — above that altitude, you could receive a second VOR on the same frequency
The same label, two very different reasons
The number tells you which
Why interference MAAs exist — the real reason:
VOR signals are line-of-sight, and line-of-sight improves with altitude
At high altitude, your receiver can “see” farther — far enough to pick up a SECOND VOR transmitting on the SAME frequency (facilities share frequencies, separated geographically on the assumption that you can’t receive both at once)
When two co-channel VORs are received simultaneously, the signals interfere and the CDI/bearing becomes unreliable
The interference MAA is the altitude above which that co-channel overlap could occur on this segment
The correction to a common misstatement:
An interference MAA is NOT about losing the signal at altitude — it’s about receiving TOO MANY signals
Higher is not worse for reception; it’s worse for interference
Frequency protection, not range
The opposite of the MOCA’s problem
Key characteristics:
Ensures navigation signal integrity (no co-channel interference), not obstacle clearance
Published on Victor airways, jet routes, and RNAV routes (T-routes and Q-routes)
On Victor airways, “MAA-17500” usually reflects the structural top of the low-altitude airway system; a lower, segment-specific MAA reflects a co-channel interference analysis
On RNAV routes, the MAA reflects the airspace structure: T-routes typically MAA-17500, Q-routes typically MAA-FL450
Chart depiction:
Shown as “MAA-17500” (or similar) on the route segment, usually near the MEA
Text, not a flag
Easy to miss because the structural 17,500 value is so routine
The one to notice is a segment with an MAA well below 17,500
Operational considerations:
ATC will not normally assign an altitude above the MAA for that route segment
If you’re filed above it, expect a different altitude or a reroute
A GPS-navigating aircraft on a Victor airway doesn’t suffer VOR co-channel interference, but the airway’s published MAA still applies to the airway and ATC applies it — the route’s limit governs, not your receiver
On RNAV routes the MAA is structural, so it applies regardless of equipment
A worked example:
V-123, segment MEA 6,000, MAA-11000 on one segment (a co-channel interference finding — note it’s well below the usual 17,500)
You file 13,000 for a tailwind
ATC assigns 11,000 for that segment, or reroutes you
Above 11,000 on that segment, a second VOR on the same frequency could be received and corrupt your indication — an error you’d never detect from the CDI alone
The MAA protects you from a navigation error, not a terrain one
MRA — Minimum Reception Altitude
What it is:
The LOWEST altitude at which an intersection can be determined — in practice, the lowest altitude at which the OFF-ROUTE navaid signal that defines the fix can be reliably received
Applies to a specific fix, not a segment
About signal reception only
Does NOT guarantee obstacle clearance
Why MRAs exist:
Many intersections on an airway are defined by a crossing radial from a VOR that’s OFF the airway
That off-route VOR may be far away or behind terrain
At the segment’s MEA, you might be able to receive the airway VORs (that’s what the MEA guarantees) but NOT the off-route VOR that identifies the intersection
The MRA is the altitude at which that off-route signal becomes receivable
The MEA/MRA relationship:
The MEA guarantees the signals that DEFINE the airway (the VORs at each end)
The MRA addresses a DIFFERENT signal: the one from the off-route VOR that identifies a specific intersection
So the MRA can be — and often is — HIGHER than the MEA
Different signal, different altitude
The nuance most pilots miss — when the MRA actually applies:
The MRA requires a climb ONLY if you need to identify the fix USING that off-route VOR radial
If you identify the fix by DME from an on-airway facility, the MRA’s purpose isn’t engaged (DME is a different signal)
If you identify it by GPS (an IFR-approved GPS can identify any charted fix), you don’t need the off-route signal at all
If you DON’T NEED to identify the fix (you’re just passing through on the airway, with no clearance limit, hold, or MEA change there), the MRA imposes nothing
The MRA is a tool for one identification method, not a segment minimum
When you DO need to identify the fix (and the MRA matters):
The fix is your clearance limit (you must know when you reach it)
You’re holding at the fix
The MEA changes at the fix (you need to know when to climb/descend)
You’re required to report passing it
ATC asks you to report it
In these cases, if you’re identifying by the off-route radial, climb to the MRA
Chart depiction:
A flag symbol containing an “R” adjacent to the fix
With the altitude text, e.g., “MRA 7000”
The flag is the cue; the number is the altitude
Look for the R flag at intersections
Practical example:
V-456, segment MEA 5,000
BRAVO intersection is defined by the 090 radial of a VOR 40 NM north, behind a ridge
MRA 7,000 at BRAVO (R flag)
Scenario A: you’re on GPS, cleared to a fix beyond BRAVO — identify BRAVO by GPS, stay at 5,000, MRA irrelevant
Scenario B: you’re VOR-only, cleared to BRAVO as a clearance limit (expect further clearance) — you must identify it; climb to 7,000 to receive the off-route radial, identify BRAVO, then (if the MEA allows and ATC agrees) you may return to 5,000
Scenario C: you’re VOR-only, just passing BRAVO en route with no need to identify it — stay at 5,000
Pilot responsibility:
Know HOW you’re identifying each fix that matters
If it’s by an off-route radial, check for an R flag and the MRA
Request the climb from ATC if needed (“Request 7,000 to identify BRAVO”)
The MRA doesn’t change the MEA — it’s a temporary need
MCA — Minimum Crossing Altitude
What it is:
The LOWEST altitude at which a fix must be CROSSED when continuing in a specified direction, to ensure obstacle clearance AFTER the fix
Applies at a specific fix, in a specific direction
About obstacle clearance beyond the fix
May be higher than the MEA of the segment you’re leaving
Why MCAs exist:
Normally, when the MEA increases at a fix, you may start climbing when you pass the fix (91.177(b))
But sometimes the terrain beyond the fix rises so steeply that starting the climb at the fix — at a normal climb gradient — won’t keep you clear of it
The solution: require you to ALREADY be at a higher altitude when you cross the fix
The MCA bridges the gap between the lower segment’s MEA and the terrain beyond
The regulation — 91.177(b):
“Climb to a higher minimum IFR altitude shall begin immediately after passing the point beyond which that minimum altitude applies, except that when ground obstructions intervene, the point beyond which that higher minimum altitude applies shall be crossed at or above the applicable MCA.”
No MCA: climb starts after the fix
MCA published: you must be at or above it AT the fix — so the climb starts BEFORE the fix
The regulation makes the MCA mandatory
Key characteristics:
Ensures obstacle clearance beyond the fix
Applies only at the specific fix, in the stated direction (an MCA eastbound may not apply westbound)
Often higher than the MEA you’re leaving
Common in mountainous terrain where MEAs step up sharply
Chart depiction:
A flag symbol containing an “X” adjacent to the fix
With text naming the airway, altitude, and direction, e.g., “MCA V12 7000 NE”
The direction matters: the MCA applies only when continuing in that direction
Several MCAs may be listed at one fix (one per airway/direction)
Reading the text:
“MCA V12 7000 NE” = on V12, continuing northeast, cross this fix at or above 7,000
If you’re on V12 southwest-bound, that MCA doesn’t apply to you (check for a separate one)
Airway + altitude + direction, all three
Read the whole string
Pilot responsibility:
You must REACH the MCA before crossing the fix — which means planning the climb to arrive at the fix already at that altitude
ATC may not remind you — the MCA is a pilot responsibility on your own navigation
Compute when to start the climb: altitude to gain ÷ your climb rate = minutes before the fix (then convert to distance at your groundspeed)
Critical for performance-limited aircraft in high terrain
A worked example:
V-789 northbound: segment A (south of PAPA) MEA 6,000; segment B (north of PAPA) MEA 10,000; PAPA has “MCA V789 8500 N” (X flag)
Without an MCA, you’d start climbing at PAPA and reach 10,000 some miles north — but the ridge is right there, so the designers published an MCA
Your aircraft climbs 500 fpm at 100 kt groundspeed
You must cross PAPA at or above 8,500: that’s 2,500 feet to gain from 6,000 → 5 minutes → start the climb about 8 NM before PAPA
After PAPA, continue climbing to 10,000 (the new MEA)
Request the climb from ATC early enough to make it
The MEA-increase comparison:
MEA increases at a fix, no MCA → climb begins after the fix
MEA increases at a fix, MCA published → be at the MCA when you cross, then continue to the MEA
The MCA is the “start early” instruction
Look for the X flag at every MEA step-up
OROCA — Off-Route Obstruction Clearance Altitude
What it is:
A GRID-based altitude providing obstacle clearance for flight OFF published airways
One value per latitude/longitude quadrangle on the en route chart
The IFR counterpart to the sectional’s MEF, but with the clearance built in
For direct routes, deviations, and emergencies
What the OROCA provides:
Obstacle clearance only: 1,000 feet above the highest obstruction in non-mountainous areas, 2,000 feet in designated mountainous areas
Within the entire quadrangle (not along a specific course)
A conservative, area-wide floor
Terrain and obstacles, nothing else
What the OROCA does NOT provide:
Navigation signal reception (no guarantee you can receive any navaid)
Communication coverage (no guarantee you can reach ATC)
ATC radar coverage
Any assurance about airspace (controlled vs. uncontrolled)
Chart depiction:
Large, bold numbers inside each grid quadrangle on IFR en route low-altitude charts
The format uses a large digit (thousands) with a smaller raised digit (hundreds): e.g., 12⁵ = 12,500 feet; 8³ = 8,300 feet
One value per 1° × 1° box
The highest obstacle in the box plus the clearance
The relationship to 91.177(a)(2):
When you’re off an airway with no published minimum, 91.177(a)(2) requires 1,000 feet (non-mountainous) or 2,000 feet (mountainous) above the highest obstacle within 4 NM of your course
The OROCA is built on exactly those clearance values, applied to the whole quadrangle
So flying at or above the OROCA satisfies the 91.177 off-route rule for that box
A ready-made compliance tool
Typical uses:
Planning an off-airway or direct route (check every grid box your course crosses)
Evaluating a direct-to clearance (ATC’s MIA governs the assignment, but you verify terrain clearance)
Emergency off-route navigation (you need a safe altitude NOW and you’re not on an airway)
Deviating around weather off the airway
What it’s NOT for:
The lost-communications altitude (that’s the highest of MEA/expected/assigned — 91.185)
A substitute for the MEA on an airway (on an airway, the MEA is the floor)
A guarantee you can navigate or communicate at that altitude
A planning tool, not an operating guarantee
The conservatism caveat:
The OROCA covers the HIGHEST obstacle in a box that’s roughly 60 NM on a side
If one peak in the corner is 11,000 feet, the whole box carries 13,000 — even over the valley on the other side
Usable, but often much higher than a route-specific analysis would require
Conservative by design
A worked example:
Cleared direct from ALPHA to CHARLIE, off airways, crossing two grid boxes
Box 1 OROCA: 7² (7,200); Box 2 OROCA: 10⁴ (10,400)
To satisfy 91.177 via the OROCA, you need 10,400 for the portion in Box 2 — and since you can’t be sure exactly where the box boundary falls relative to your course, the conservative plan is 10,400 (or the next hemispheric altitude above it, 11,000 eastbound) for the whole direct leg
ATC may assign something lower based on their MIA — that’s their responsibility while they have you on radar; the OROCA is your independent check
MTA — Minimum Turning Altitude
A newer en route altitude worth knowing.
What it is:
A minimum altitude for making a TURN at a specific fix, navaid, or waypoint — published where the published MEA isn’t sufficient for obstacle clearance during the turning maneuver
Applies at the fix, for the turn, in the stated direction
Added to charts in recent years
Why it exists:
At or above 10,000 feet MSL, aircraft fly faster (the 250-knot limit below 10,000 no longer applies), and a faster aircraft has a larger turn radius
When an airway turns at a fix, that larger radius carries the aircraft farther outside the normal protected area during the turn
The designers examine an expanded area around the turn; where terrain in that expanded area (usually mountainous) isn’t cleared by the published MEA, they publish an MTA — a higher minimum altitude for the turning maneuver
A high-altitude, high-airspeed refinement of obstacle protection
Chart depiction:
A flag at the fix with accompanying text describing the MTA restriction (the airways involved, the altitude, and the direction of the turn)
Similar in style to the MCA
Still relatively uncommon
Look for it at airway turns in mountainous terrain, particularly on segments at or above 10,000 feet
MVA and MIA — ATC’s Altitudes
For completeness: the altitudes ATC uses, which you won’t find on your chart.
MVA — Minimum Vectoring Altitude:
ATC’s minimum altitude for radar vectoring in each area of a terminal/approach sector
Based on radar coverage and obstacles, often LOWER than the MEA (radar can see terrain the airway design can’t rely on)
On ATC’s charts, not yours
When you’re on vectors, ATC assumes terrain responsibility using the MVA
MIA — Minimum IFR Altitude:
ATC’s minimum altitude in Center (en route) sectors, for non-airway assignments
Similar concept to the MVA for Center airspace
Also on ATC’s charts
What ATC uses to assign a direct-route altitude
Why they matter to you:
They explain how ATC can legally assign you an altitude below the MEA (on vectors) or off an airway (on a direct)
While ATC has you on radar and assigns the altitude, terrain clearance is their responsibility
When you “resume own navigation,” the published altitudes (MEA/OROCA) are yours again
Know whose altitude you’re on
Putting It Together: A Comparison
Altitude | Floor or ceiling? | Applies to | Guarantees | Chart cue |
MEA | Floor | Segment | Obstacles + nav signal (whole segment) | Bold number |
MOCA | Floor (conditional) | Segment | Obstacles + VOR signal within 22 NM | *Number |
MAA | Ceiling | Segment | Usable top of the route (structural) or freedom from co-channel interference (segment-specific) | “MAA-17500” |
MRA | Floor (for one purpose) | Fix | Reception of an off-route navaid to identify the fix | R flag |
MCA | Floor (at the fix) | Fix, by direction | Obstacle clearance beyond the fix | X flag, “MCA V12 7000 NE” |
MTA | Floor (for the turn) | Fix, by direction (10,000+ MSL) | Obstacle clearance during a high-speed turn | Flag at the fix |
OROCA | Floor | Grid box (off-route) | Obstacles only (1,000/2,000 ft); no nav/comm | Large grid number (12⁵) |
MVA / MIA | Floor (ATC’s) | ATC sector | Obstacles (ATC’s responsibility on vectors/directs) | Not published |
Briefing the Fix-Specific Altitudes
A practical habit the original mentions — here’s what it looks like.
At every fix on your route, ask:
Does the MEA change here? (T-bar) → if up, is there an MCA (X flag)? If so, plan the climb to arrive at it
Do I need to identify this fix, and how? → if by an off-route radial, is there an MRA (R flag)? If so, plan the climb
Is there a turn at or above 10,000 feet in terrain? → MTA?
Is there an MAA on the next segment that caps my altitude — and is it the routine 17,500 or something lower?
For any off-airway portion:
What’s the OROCA for each grid box? Does my altitude satisfy it (or 91.177 directly)?
Am I on ATC’s MIA (their responsibility) or my own navigation (mine)?
The payoff:
No surprise climbs, no missed MCAs, no unidentifiable clearance limits
A two-minute brief that removes the most common en route altitude errors
Fix by fix, before departure
Comprehension over compliance
Common Pilot Mistakes
Assuming the OROCA guarantees navigation or communication coverage (it guarantees obstacles only)
Using the OROCA as the lost-communications altitude (the rule is the highest of MEA/expected/assigned)
Ignoring an MCA and starting the climb at the fix (the MCA requires you to be at the altitude when you cross)
Reading an MCA without its direction (an eastbound MCA doesn’t apply westbound)
Climbing to the MRA unnecessarily when identifying the fix by DME or GPS (the MRA applies only to the off-route radial method)
Confusing the MRA with the MEA (the MRA is for identifying one fix; the MEA is the segment floor)
Thinking an interference MAA is about losing signal at altitude (it’s about co-channel interference from a second VOR)
Assuming GPS negates the MAA (the route’s published MAA applies regardless of your receiver, on Victor and RNAV routes alike)
Failing to brief the fix-specific flags (R, X) before the flight
Not computing when to start a climb to meet an MCA in a slow-climbing aircraft
Checkride Questions — With Answers
“What is the MAA, and why does it exist?”
The Maximum Authorized Altitude — the highest usable altitude on a route segment at which adequate navigation signal reception is assured. It’s a ceiling, not a floor. On Victor airways, “MAA-17500” usually reflects the structural top of the low-altitude airway system; a lower, segment-specific MAA reflects co-channel interference — at higher altitudes you can receive a second VOR on the same frequency, corrupting the indication. RNAV routes carry structural MAAs too (T-routes 17,500; Q-routes FL450). Shown as “MAA-XXXXX.”
“What is the MRA, and when must you climb to it?”
The Minimum Reception Altitude — the lowest altitude at which an intersection can be determined, i.e., at which the off-route navaid defining the fix can be received. You must climb to it only if you need to identify the fix using that off-route radial. If you identify it by DME or GPS, or don’t need to identify it, the MRA doesn’t apply. It does not provide obstacle clearance. Shown with an “R” flag.
“What is the MCA, and when does it apply?”
The Minimum Crossing Altitude — the altitude at or above which you must cross a fix when continuing in a specified direction, so you clear terrain beyond it. Per 91.177(b), when an MCA is published you must be at it when you cross (start climbing before the fix); without one, you climb after the fix. Shown with an “X” flag and the airway/altitude/direction.
“What does the OROCA provide, and what doesn’t it?”
Obstacle clearance — 1,000 feet (non-mountainous) or 2,000 feet (mountainous) above the highest obstruction in the grid quadrangle. It does not guarantee navigation signal reception, communications, or radar coverage. It’s for off-route planning and emergencies, not a substitute for the MEA and not the lost-comms altitude.
“What is an MTA?”
The Minimum Turning Altitude — a higher minimum for a turn at a fix at or above 10,000 feet MSL, where higher airspeeds enlarge the turn radius beyond the normal protected area and the published MEA may not clear terrain in the expanded area. Charted with a flag and descriptive text.
“Can ATC assign you below the MEA?”
Yes, on radar vectors using their MVA (or on a direct using their MIA), while they assume terrain responsibility. When you resume your own navigation, the published altitudes apply.
“How do you know an MCA applies to your direction?”
The MCA text names the airway and direction (e.g., “MCA V12 7000 NE”). It applies only when continuing in that direction on that airway.
Final Thoughts
Each of these altitudes exists to solve a specific operational problem. The MAA caps the route — usually because the airway structure ends at 17,999 feet, and occasionally, on a specific segment, because a second VOR on the same frequency could corrupt your navigation above it. The MRA tells you how high you need to be to receive an off-route navaid — but only if that’s how you’re identifying the fix. The MCA tells you to arrive at a fix already climbing, because the terrain beyond it won’t wait for a normal climb to begin. The MTA does the same for a high-speed turn at altitude. And the OROCA gives you a safe floor for the spaces between the airways, with no promise of navigation or communication once you’re there.
The chart flags — R for reception, X for crossing, the MAA text, the big grid numbers — are small and easy to skim past, but each one is a trigger worth briefing fix by fix before you depart. Understanding how MAA, MRA, MCA, and OROCA differ lets you fly safer in complex airspace, anticipate altitude changes, reduce workload, and answer checkride questions with confidence. Instrument flying isn’t just about compliance — it’s about comprehension.
On the Written Test and Checkride
These altitudes appear on every instrument written and oral. The most commonly tested topics:
The MAA as a ceiling (structural on most airways; co-channel interference on specific segments; not obstacles)
The MRA (reception of an off-route navaid; no obstacle clearance; when it actually requires a climb)
The MCA and 91.177(b) (be at it when crossing the fix; direction-specific)
The OROCA (1,000/2,000 ft; obstacles only; no nav/comm guarantee; not for lost comms)
The MTA (10,000+ MSL turns)
Chart depiction (R flag, X flag, MAA text, grid numbers)
MVA/MIA and why ATC can assign below the MEA
Quick Reference
MAA — Maximum Authorized Altitude:
The CEILING for a route segment (maximum usable altitude with assured nav signal)
Two sources: structural (Victor airways MAA-17500 = top of the low-altitude system; T-routes 17,500; Q-routes FL450) and interference (a lower, segment-specific MAA where a second co-channel VOR could be received — line-of-sight improves with altitude)
Not about obstacle clearance
Chart: “MAA-17500” text on the segment — notice the ones below 17,500
ATC won’t assign above it; applies regardless of your receiver, on Victor and RNAV routes alike
MRA — Minimum Reception Altitude:
Lowest altitude to receive an OFF-ROUTE navaid to identify a fix
Does NOT provide obstacle clearance; often higher than the MEA
Applies ONLY if you identify the fix by that off-route radial — not by DME, not by GPS, and not if you don’t need to identify it
Matters when the fix is a clearance limit, hold, MEA change, or reporting point
Chart: R flag + “MRA 7000”
MCA — Minimum Crossing Altitude:
Altitude you must be at or above when CROSSING a fix in a stated direction (obstacles beyond the fix)
91.177(b): with an MCA, be at it when you cross (climb before the fix); without one, climb after the fix
Direction-specific
Chart: X flag + “MCA V12 7000 NE” (airway, altitude, direction)
Plan the climb: altitude to gain ÷ climb rate = minutes before the fix
OROCA — Off-Route Obstruction Clearance Altitude:
Grid-box altitude: 1,000 ft (non-mountainous) / 2,000 ft (mountainous) above the highest obstruction in the quadrangle
Obstacles ONLY — no navigation, communication, or radar guarantee
Chart: large grid number with a raised hundreds digit (12⁵ = 12,500)
Satisfies 91.177(a)(2) for the box
For off-route/direct planning and emergencies — NOT the lost-comms altitude, NOT a substitute for the MEA
Conservative (covers the highest obstacle in a ~60 NM box)
MTA — Minimum Turning Altitude:
Minimum altitude for a turn at a fix at or above 10,000 ft MSL, where higher airspeeds enlarge the turn radius beyond the normal protected area (usually mountainous terrain)
Chart: flag at the fix with descriptive text (airways, altitude, direction)
Uncommon; look for it at high-altitude airway turns in terrain
MVA / MIA (ATC’s):
Minimum Vectoring Altitude (terminal) / Minimum IFR Altitude (Center)
Not on your chart; often below the MEA
ATC’s responsibility while vectoring or on a direct; yours again when you resume own navigation
The Comparison:
Applies to | Floor/ceiling | About | |
MAA | Segment | Ceiling | Route structure / interference |
MRA | Fix | Floor (to identify) | Off-route signal |
MCA | Fix (direction) | Floor (at the fix) | Obstacles beyond |
MTA | Fix (direction, 10,000+) | Floor (for the turn) | Obstacles during a high-speed turn |
OROCA | Grid box | Floor | Obstacles off-route |
Brief Every Fix:
MEA change (T-bar)? → MCA (X flag)? Plan the climb
Need to identify it, and how? → MRA (R flag) only if by off-route radial
Turn at or above 10,000 in terrain? → MTA
MAA on the next segment — routine 17,500 or something lower?
Off-airway? → OROCA per box (or 91.177 directly)
Key Principle:
The MAA is a ceiling — structural on most airways, co-channel interference on specific segments, and never about terrain; the MRA is a floor only for identifying a fix by an off-route radial (DME or GPS makes it irrelevant); the MCA is a floor you must already be at when crossing a fix in the stated direction (91.177(b) — climb before, not after); the MTA covers a high-speed turn at or above 10,000 feet; and the OROCA is a conservative off-route floor that clears obstacles but guarantees nothing else. Read the R and X flags, the MAA text, and the grid numbers — and brief them fix by fix.
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Author: Nathan Hodell
CFI, CFII, MEI, ATP, Creator and CEO
Nathan is an aviation enthusiast with thousands of hours of flying and dual instruction over the past 15+ years. Through his aviation career he has been able to earn his ATP, fly as an airline pilot, own/operate flight schools, and create and host wifiCFI.