Commercial pilot · ACS CA.VI.C
Diversion
A diversion is a planned change of destination, made early, with a quick estimate first and a careful one after.
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.
Can’t miss
- •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)
What you should know
When to divert K2 · R3
- 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 K1 · R4
- 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 R5
- 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 R1 · R2
- 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)
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.
Scenarios
Decide what you would do first, then see the worked answer.
The FIS-B radar picture shows your route clear of a storm, but the image is 12 minutes old.
Can you rely on it? See the worked answer
No: storms move and develop in 12 minutes. Use it for strategic avoidance only, keep a wide margin, and check with ATC or Flight Service.
AIM, Chapter 7, Safety of Flight (in-flight weather and FIS-B)
Two nearby airports: one 8 nm away with a 2,600-foot runway and a 15-knot crosswind, one 15 nm away with a long runway into the wind.
Which do you choose? See the worked answer
Usually the second: it improves the situation (longer runway, into the wind). The extra 7 miles is a few minutes.
Risk Management Handbook (FAA-H-8083-2A)
Your fuel burn is 10% above plan and the headwind is stronger than forecast.
What do you do? See the worked answer
Recompute fuel at the destination with reserve; if it drops below your personal minimum, divert to a fuel stop now.
14 CFR 91.151; RMH
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.
Now train it
Say it out loud, hear it asked, and take the quick check in this lesson’s practice pack. It tracks your shaky spots.
Got it?
When it feels solid, practice diversion out loud with our examiner.
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Teaching this? The instructor lesson plan →
Sources
- Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C): Navigation; Flight Instruments
- Advanced Avionics Handbook (FAA-H-8083-6)
- Aeronautical Information Manual (AIM): Chapters 1, 4, 6 and 7
- 14 CFR Part 91: 91.3, 91.103, 91.123, 91.151, 91.171, 91.215, 91.225
- AC 90-48 and AC 91-78
- Commercial Pilot ACS (FAA-S-ACS-7B): Area VI
Study aid, not FAA guidance. Regulations change; check the current text at eCFR and the ACS. Checked against current sources 2026-11-13.