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Commercial pilot · ACS CA.VI.C · lesson pack

Diversion

Why this one matters

For a commercial pilot, the hardest part of a diversion is often deciding to do it: the client expects to arrive where they paid to go. Weather and fuel accidents are usually the story of a diversion made too late. Setting the decision criteria before the flight, and acting on them, keeps the choice a calm one.

1 · Know these cold

  • •Divert early: weather worse than forecast, fuel burn above plan, a mechanical concern, a sick passenger, fatigue or darkness are all reasons.(Risk Management Handbook (FAA-H-8083-2A))
  • •Turn toward the new destination first, then work out heading, distance, groundspeed, time and fuel.(PHAK (FAA-H-8083-25C), Navigation)
  • •Pick the airport that makes the situation better: runway length and surface, weather, fuel, services, terrain and airspace, not just the closest.(PHAK (FAA-H-8083-25C), Navigation)
  • •Routine diversion on a clearance or in controlled airspace: get an amended clearance first (91.123). In an emergency, the PIC may deviate from the rules or a clearance to the extent required, telling ATC as soon as possible, and must send a written report if the FAA asks (91.3(b)-(c)).(14 CFR 91.3; 91.123)
  • •Use your resources: ATC, Flight Service, the GPS nearest and direct-to functions, data-link weather, and passengers for simple tasks.(Advanced Avionics Handbook (FAA-H-8083-6))
  • •Data-link NEXRAD shows where the weather was: what it depicts can be 15 to 20 minutes older than the age on the display. Use it only for strategic avoidance with wide margins, never to thread between cells.(AIM, Chapter 7, Safety of Flight (in-flight weather and FIS-B); NTSB Safety Alert SA-017)
  • •Commercial standard: select a suitable destination and route (S1), estimate heading, groundspeed, arrival time and fuel (S2), hold altitude ±100 feet and heading ±10° (S3), and divert promptly (S6).(Commercial Pilot ACS (FAA-S-ACS-7B), CA.VI.C.S1-S3, S6)

2 · The lesson

When to divert
  • Weather worse than forecast, a lowering ceiling, an unexpected headwind, fuel above plan, a rough engine, a sick passenger, fatigue or approaching darkness.(Risk Management Handbook (FAA-H-8083-2A))
  • The legal floor is 91.151: before you begin a VFR flight, fuel to the first point of intended landing plus, at normal cruise, 30 minutes by day or 45 at night, considering wind and forecast weather. The in-flight divert decision should come from a higher personal minimum (ceiling, visibility, fuel at landing) set before the flight; divert when you reach it.(Risk Management Handbook (FAA-H-8083-2A); 14 CFR 91.151)
  • Not an emergency: ask ATC for an amended clearance before turning. An emergency: deviate to the extent required, tell ATC as soon as possible, and file a report if asked.(14 CFR 91.3; 91.123)
  • With passengers who paid for the trip, decide by the criteria, explain it plainly, and offer the alternative (a later arrival, ground transport).(Risk Management Handbook (FAA-H-8083-2A))
Choosing the airport
  • Before the flight, note suitable airports along the route. In flight, check runway length and surface, weather, fuel, services, terrain, airspace and NOTAMs for the one you choose.(PHAK (FAA-H-8083-25C), Navigation)
  • Choose the airport that improves the situation: a long runway into the wind with good weather beats a slightly closer one with a crosswind and low clouds. The exception is time-critical (a seriously ill passenger, fire, a failing engine): the closest suitable airport with help (road access, EMS, a usable runway) usually wins; tell ATC, ask for priority, and declare if you need it.(Risk Management Handbook (FAA-H-8083-2A))
Doing it
  • Turn toward the new destination right away (once cleared, if on a clearance), on an estimated heading from the chart or the GPS direct-to; note the time. Pick an altitude for the new route that clears terrain, obstacles and wires (check the maximum elevation figures) and fits the cruising rule for the new magnetic course.(PHAK (FAA-H-8083-25C), Navigation; 14 CFR 91.159)
  • Then refine it: distance, groundspeed from the known wind, time and fuel. Check the GPS against the chart.(PHAK (FAA-H-8083-25C), Navigation)
  • Tell ATC; they can give vectors, weather and airport information.(AIM, Chapter 4, Air Traffic Control (radar services for VFR aircraft))
  • Update the weather from ATIS/ASOS, Flight Service or FIS-B, and check the data's age.(AIM, Chapter 7, Safety of Flight (in-flight weather and FIS-B))
Workload and traffic
  • A diversion adds workload at a stressful time: distraction, poor task priorities and lost situational awareness are the risks. Fly the airplane first, then the math.(Risk Management Handbook (FAA-H-8083-2A))
  • A new route may cross unfamiliar traffic and airspace: keep scanning, and use flight following.(AC 90-48, Pilots' Role in Collision Avoidance)

Want it all on one page, with scenarios? Read the full lesson.

On the flight

ACS standards

  • Select a suitable destination and route; estimate heading, groundspeed, arrival time and fuel; promptly divert.(Commercial Pilot ACS (FAA-S-ACS-7B), CA.VI.C.S1-S2, S6)
  • Altitude ±100 feet, heading ±10°; update and interpret weather in flight; use digital weather and aeronautical displays.(Commercial Pilot ACS (FAA-S-ACS-7B), CA.VI.C.S3-S5)

What your instructor is watching for

Your instructor watches for an early decision, an immediate turn on an estimated heading, a sensible airport choice, a reasonable estimate of time and fuel, ATC used, and altitude and heading held within commercial tolerances.

3 · Say it out loud

Answer each one out loud, then check yourself and mark how it went.

  1. Remember Recall it

    “What do you do first when you decide to divert?”

  2. Understand Explain why

    “Why decide on diversion criteria before the flight?”

  3. Apply Use it on a flight

    “Halfway, the destination's ceiling is dropping toward your minimum and your client has a meeting there. What do you do?”

4 · Common mistakes

  • Computing before turning.

    You fly further the wrong way while you work.

    Instead: Turn first on an estimate, then refine.

  • Choosing the closest airport automatically.

    It may not improve the situation.

    Instead: Pick the one that does: runway, wind, weather, services.

  • Waiting too long.

    Options shrink with fuel, weather and daylight.

    Instead: Divert when a pre-set limit is reached.

5 · Quick check

Answer, then reveal. Flag anything you want to see again.

  1. 1. Who is the final authority for the operation of the aircraft?

  2. 2. Is FIS-B weather real time?

  3. 3. What are the commercial tolerances during a diversion?

  4. 4. What makes a good diversion airport?

  5. Scenario5. Your passenger becomes ill 40 minutes from destination. What do you do?

Trained it? Now prove it: practice diversion out loud with our examiner.

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Connect it

One situation that runs across this lesson and its neighbors in the same ACS area. Decide first, then check.

Connect it · Navigation

A night cross-country. Headwinds are stronger than forecast and your groundspeed is down 25 knots.

How do your checkpoint times feed a diversion decision? Decide, then see the worked answer

Compare the actual time at each checkpoint with the plan. A 25-knot shortfall stretches every leg, so recompute the fuel to the destination at the actual groundspeed. Keep the reserve separate: 91.151(a)(2) requires enough fuel at night to reach the destination and then fly 45 more minutes at normal cruising speed, so add 45 minutes at normal cruise on top of the destination fuel. That's the legal floor; a personal minimum can raise it but never lower it. If you'd land with less than your minimum, divert now, while you still know exactly where you are. At night, choose the alternate with the Chart Supplement: runway lighting and how it's activated, runway length and surface, and whether fuel is actually available at that hour. Note the time and heading as you turn, estimate heading, time and fuel to the new airport, then refine. Leaving it late, at night, is how being short of fuel turns into being lost.

14 CFR 91.151; PHAK (FAA-H-8083-25C), Navigation; Chart Supplement

Brings together: Pilotage and Dead Reckoning · Diversion

Teaching this? The instructor lesson plan →

Study aid, not FAA guidance. Sources: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C); Advanced Avionics Handbook (FAA-H-8083-6); Aeronautical Information Manual (AIM); 14 CFR Part 91; AC 90-48 and AC 91-78; Commercial Pilot ACS (FAA-S-ACS-7B). Checked against current sources 2026-11-13.