Clearances, Departure & Enroute

Pilot & Controller Responsibilities

Pilot in command per 14 CFR § 91.3 — final authority and responsibility for the aircraft. Specifically:

• Plan the IFR flight: route, altitudes, fuel, weather, NOTAMs
• File the flight plan with the appropriate ATC facility
• Comply with ATC instructions (or immediately advise inability)
• Maintain navigation accuracy and report deviations promptly
• Conduct approaches per published procedures
• Read back and acknowledge clearances; communicate any doubt

Three ATC facility types you'll work with on an IFR flight:

• Control Tower: Manages the local airport and immediate surrounding airspace. Issues takeoff/landing clearances, ground/airspace transitions, traffic separation in the terminal area.
• TRACON (Terminal Radar Approach Control): Bridge between airport tower and en route structure. Mostly Class B and C airports; some busy Class D have their own. May be divided by sector. Uses Airport Surveillance Radar (ASR).
• ARTCC (Air Route Traffic Control Center, "Center"): Provides separation between IFR traffic in the en route structure. Divided into large sectors and altitudes (high/low). Frequencies in the back of the chart supplement and on en route charts.

Requesting a Clearance

On the ground: Use Clearance Delivery if available. Otherwise Ground Control. At a non-towered airport, FSS (Flight Service) or call-out via the published clearance phone number in the chart supplement.

Standard request: "[Facility] Clearance, [Callsign] is at [Location] with information [ATIS letter], IFR to [Destination], ready to copy."

From the air: "[Approach/Center], [Callsign] is at [Location] with IFR request." You'll get either "go ahead with your request" or "standby." Often a squawk code right away so they can establish radar contact.

Radar contact means ATC has identified your aircraft on radar and will provide flight following until terminated. Once in radar contact you stop reporting compulsory reporting points. Radar contact lost means radar service is suspended — you go back to position reports.

The CRAFT Acronym — Parts of a Clearance

ATC delivers clearances in this exact order. Set up your scratchpad with C / R / A / F / T pre-written and check off each as it's read.

• C — Clearance limit: The endpoint of the clearance. Usually but not always your destination airport.
• R — Route: The route ATC has assigned. Often what you filed, sometimes amended. "Cleared as filed" shortcuts this when nothing changed.
• A — Altitude: Initial altitude to maintain, plus the time at which to expect cruise altitude clearance ("expect 8,000 in 10 minutes")
• F — Frequency: Departure frequency to tune after takeoff
• T — Transponder code: The squawk code to set before departure. T also stands for Time when a void time is issued.

Five Steps to Receiving a Clearance

1. Copy — write everything down using shorthand. Don't try to interpret as it's read; just transcribe what you hear. If you fall behind, ask for a re-read at a slower pace.
2. Read back — read what you wrote. This confirms recording, not acceptance. Acceptance happens at takeoff.
3. Study — pull out your charts and trace the route end-to-end. Verify it makes sense, that the airways link to the fixes named, and the route actually leads to your destination. Long trips deserve several minutes of checking.
4. Request changes / clarification — if the route is too circuitous or the altitude is in stronger winds, ask. Better to fix it on the ground than carry a confused clearance into IMC.
5. Set up the radios — frequencies, courses, baro, transponder. Do as much as possible on the ground so you're not fiddling at 200 ft AGL transitioning to instruments.

Even after "readback is correct," there's no guarantee the controller heard exactly what you read. If something feels off, ask again.

Clearance Void Times (Non-Towered)

At airports without a control tower, clearances often include a void time — if you're not airborne by that time, the clearance is void.

• If you can't depart by the void time, advise ATC ASAP of intentions
• If you don't contact ATC within 30 minutes after the void time, you're considered overdue and search and rescue is initiated
• Other IFR traffic into that airport is suspended until you contact ATC, the 30-minute window expires, or 30 minutes after release time if no void time was issued
• If you depart at or after the void time, you have no IFR separation and are in violation of 14 CFR § 91.173
• If you choose to depart VFR after the void time expires, do not use the previously assigned IFR squawk code

Standard phraseology: "Clearance void if not off by [time]; if not off by [time] advise [facility] not later than [time] of intentions."

IFR Takeoff Minimums

• Part 91 operators: No standard takeoff minimums. Legally, zero-zero is permitted — though "legal" and "smart" diverge here.
• Part 121/135 (commercial) — 1 or 2 engines: 1 SM visibility
• Part 121/135 — 3+ engines: 1/2 SM visibility
• Part 121/135 — Helicopters: 1/2 SM visibility

The "Troubled T" symbol (a black triangle with "T" inside) on the approach plate means takeoff minimums, diverse vector area information, or obstacle departure procedures are published in a separate document. Look it up before departing in IMC — there's terrain or obstacles dictating non-standard requirements.

Obstacle Departure Procedure (ODP)

An ODP provides obstacle clearance via the least difficult route from the terminal area to the en route structure. Established when high terrain or obstacles surround the airport.

• Available in textual or graphical form, published in the TPPs (Terminal Procedures Publication)
• May be flown without an ATC clearance — pilot's option
• ATC assumes the pilot uses the published ODP when departing a non-towered airport
• Standard climb minimums: 35 ft above DER (Departure End of Runway), 200 ft/NM minimum climb gradient, 400 ft AGL before first turn
• Higher minimums published as needed (e.g., 570 ft/NM until 2,000 ft)

Standard Instrument Departure (SID)

Pre-published departures that provide obstacle clearance and reduce ATC/pilot workload at high-traffic airports.

• Available only in graphical form
• ATC clearance required to fly a SID
• Same minimum climb requirements as ODP: 35 ft / 200 ft per NM / 400 ft AGL before first turn (often higher per the specific SID)
• The pilot must have the SID chart in their possession
• You can decline a SID by including "NO SID" in your flight plan remarks

Radar Departure

For airports without a published departure, when you can't comply with the published procedure, or when "NO SID" was filed.

• Tower coordinates closely; ATC vectors you immediately after takeoff
• Navigation is the controller's responsibility until the verbiage "resume own navigation"
• Common at Class B, C, and busier Class D airports

VFR Departure

When weather permits, take off VFR and pick up your IFR clearance in the air. Useful at non-towered airports without published departures, or when ground delays would otherwise be long.

• If you accept an IFR clearance below the minimum IFR altitude for your area, you are responsible for terrain and obstacle clearance until reaching filed altitudes — ATC is not
• Maintain VFR cloud clearance the entire time you're below your IFR clearance altitude

Enroute Altitudes

• MEA — Minimum Enroute Altitude: Guarantees a usable nav signal from at least one VOR defining the airway over the entire segment. If a stretch loses signal it's labeled "MEA gap" — dead reckon until reception is restored.
• MRA — Minimum Reception Altitude: The lowest altitude at which an off-course NAVAID signal can be received to identify a fix. Used when MRA > MEA at a particular fix.
• MOCA — Minimum Obstruction Clearance Altitude: Provides obstacle clearance and nav signal reception within 22 NM of a VOR. May be lower than MEA — use only within VOR reception range.
• MCA — Minimum Crossing Altitude: The lowest altitude at which a fix can be crossed when proceeding into a higher MEA segment.
• MSA — Minimum Sector Altitude: Provides at least 1,000 ft clearance over obstacles within a sector of a 25 NM circle around a navaid. Found on approach plates as an emergency reference.
• OROCA — Off-Route Obstruction Clearance Altitude: Provides 1,000 ft clearance above the highest obstacle in non-mountainous areas, 2,000 ft in mountainous. Does not guarantee nav signal or ATC reception — purely an obstacle reference for off-airway flight.

Changeover Point (COP)

The point along an airway segment between two adjacent VORs where the pilot should switch the navigation receiver from the station behind to the station ahead. Established to prevent loss of nav guidance and frequency interference.

• Usually depicted at the midpoint of a long segment, but not always — published COPs handle non-standard cases
• Switch is made at the COP, not before — you may not have reception of the next station yet
• "Pilots are urged to observe COPs to the fullest extent."

VFR-on-Top

An ATC authorization for an IFR aircraft to operate in VFR conditions at an appropriate VFR altitude. Combines IFR routing with VFR cruising flexibility — useful when a layer obscures the surface but cruise altitude is clear.

• Comply with VFR visibility and cloud clearance criteria (the IFR rules don't relax just because you have a clearance)
• Comply with minimum IFR altitudes (MEA, MOCA, etc.)
• Altitude rule: add 500 ft to the corresponding IFR cruising altitude
  • Magnetic course 0–179°: odd thousands + 500 (3,500 / 5,500 / etc.)
  • Magnetic course 180–359°: even thousands + 500 (4,500 / 8,500 / etc.)
• References: AIM 4-4-8 (IFR Clearance VFR-on-Top), AIM 5-5-13 (VFR-on-Top)

ARTCC ("Center") Services

• Issues route clearances and re-routes
• Provides vectors when needed (asks for intentions when planning your descent into an approach control's airspace)
• Issues NOTAMs en route
• Provides current weather, SIGMETs, AIRMETs as required
• Center control on airways begins at 1,200 ft AGL

Inability to Comply

If you cannot comply with a clearance — equipment failure, weather, performance, fuel — tell ATC immediately. Don't accept a clearance you can't fly. The captain has the final authority; using it is part of the job.

Common phrases:

• "Unable due to [reason], request [alternative]."
• "Negative, [reason], request lower altitude."
• "Standby — verifying [chart / weight / fuel]."

Read-Back Standard Phraseology

Always read back:

• Altitude assignments and changes
• Vectored headings
• Altitude restrictions ("at or above," "at or below," "cross at")
• Clearances and clearance limits
• Hold instructions
• Approach clearances (with the cleared approach name and runway)
• Runway assignments, hold-short instructions, taxi clearances
• Frequency changes

Brevity is good — but precision is non-negotiable. "Cleared ILS Runway 16 Right, Helicopter 969MH" is better than "cleared the approach."