Learn how pilots plan an in-flight diversion: choose a suitable airport, recalculate fuel, tell ATC, update the FMS and brief the arrival.
Pilots plan and fly an in-flight diversion by first controlling the aircraft, then choosing a reachable, suitable airport, checking weather, fuel, runway and approach options, and replanning the route and descent. They coordinate with ATC as applicable, update the navigation system, brief the arrival, monitor conditions and remain ready to change the plan again.
For our Aviation & Real-World Flying readers, the governing priority is aviate, navigate, communicate—in that order. Aircraft checklists, operating procedures and national regulations take precedence over any general sequence described here.
What makes an airport suitable for a diversion?
A suitable diversion airport is reachable with an acceptable fuel margin and can safely accommodate the aircraft, crew, passengers and reason for diverting. The airport shown first on a GPS or FMS nearest-airport page may be close but unusable.
- Fuel and reachability: Calculate predicted landing fuel using the actual fuel remaining, present wind, route, altitude, descent, likely vectors, approach and possible missed approach. Do not treat the original flight-plan prediction as measured fuel.
- Weather: Check observations, forecasts and trends, including wind, visibility, cloud base, thunderstorms, icing and runway contamination. A marginal airport may cease to be suitable before arrival.
- Runway performance: Confirm runway length, width, surface, slope, condition and crosswind against the aircraft’s landing limits and performance data. A runway being long enough when dry does not prove it is suitable when wet or contaminated.
- Approach and terrain: Consider available instrument or visual approaches, approach minima, navigation-aid status, lighting, terrain and whether the crew and aircraft are authorised and equipped for the procedure.
- Airport status and support: Check operating hours, closures, rescue cover, parking, fuel, maintenance and passenger handling. These matter less than immediate safety during an emergency but can distinguish between otherwise equal choices.
- Route to the airport: Account for terrain, restricted airspace, weather cells and any aircraft limitation. A direct line is not automatically a safe route.
The filed alternate is only a planning option; pilots are not obliged to divert there if another airport has become safer or more practical. On longer flights, crews and dispatchers often identify candidates before departure. Our explanation of how weather, airspace, fuel and diversion options shape a route shows why the safest plan is not always the shortest one.
How do pilots execute an in-flight diversion?
The safest method is a short, disciplined sequence that prevents airport selection and FMS work from distracting the crew from flying.
- Stabilise the aircraft. Establish a safe attitude, altitude and flight path. Use a reliable autopilot if appropriate, but verify its modes rather than assuming it is doing what was intended.
- Define the problem and urgency. Smoke, fire, engine trouble or severe icing may demand the nearest suitable landing with little planning time. Deteriorating destination weather or a passenger issue may allow a broader comparison.
- Establish position and endurance. Record present position, usable fuel, actual fuel flow and predicted endurance. Include any aircraft limitation that affects altitude, speed, runway choice or approach capability.
- Build a shortlist. Use charts, an electronic flight bag, dispatch information, ATC assistance and the navigation system’s nearest-airport function. Treat that function as a list of candidates, not a decision.
- Compare the candidates. Check weather, runway performance, approaches, terrain, airport availability and fuel to landing. Eliminate airports that fail a hard requirement before comparing convenience.
- Choose the route and commit. Decide early enough to preserve fuel and descent distance. Identify a backup in case weather, traffic or airport status changes again.
- Coordinate the change. Obtain an amended IFR clearance when required, or advise ATC and request assistance under VFR. Inform cabin crew, passengers and operational staff as workload and circumstances permit.
- Monitor the new plan. Recheck weather, fuel prediction, aircraft status and arrival geometry. A diversion decision is not permanent if the chosen airport becomes unsuitable.
What should pilots tell ATC during a diversion?
Pilots should give ATC the call sign, requested diversion airport, concise reason, desired route or heading, altitude request and any urgency affecting the clearance. A typical non-emergency request is “Call sign, request diversion to [airport] due [reason]”, followed by the requested routing if needed.
Under IFR, the FMS route must not replace the ATC clearance. Except when immediate emergency action is necessary, the crew should receive and read back the amended clearance before leaving the cleared route or altitude. Under VFR, flight following does not itself authorise entry into airspace requiring clearance or flight into instrument conditions.
ATC can provide vectors, airport information and priority, but the pilot in command remains responsible for airport suitability and landing performance. When an abnormal situation threatens safety or requires priority, crews use the applicable urgency or distress declaration rather than presenting it as a routine destination change.
A diversion is not automatically an emergency. However, fire, smoke, serious system failures, critical medical events or inadequate fuel margin may justify an urgency or distress call. Minimum fuel is generally an advisory that little or no delay can be accepted, not an emergency declaration; predicted landing fuel below the required final reserve calls for the applicable fuel-distress procedure. Exact terminology varies by jurisdiction and operator.
How do pilots reprogramme the FMS and brief the arrival?
Pilots reprogramme the FMS only after stabilising the aircraft and deciding on a route that matches the clearance. One pilot should keep flying and monitoring while the other edits and verifies the route whenever two qualified pilots are available.
- Confirm the correct airport identifier and position; similar identifiers and nearby airports are a common source of errors.
- Insert the new destination and cleared route, then inspect every leg, route discontinuity, altitude constraint and the active waypoint before execution.
- Check the first commanded turn. An incorrectly activated direct-to leg can produce a reversal or a turn towards terrain, weather or restricted airspace.
- Load an arrival or approach only when it is appropriate to the expected clearance. Loading a procedure does not constitute clearance to fly it.
- Update landing weight, runway, wind, runway condition and relevant performance entries. Changing the destination can remove or invalidate earlier arrival data.
Our guide to how GPS, inertial, radio and FMS navigation work together explains what the system is calculating and why independent cross-checks still matter.
The arrival brief should cover runway, approach type, minimums, terrain, missed-approach procedure, weather, landing performance and the plan after a go-around. Pilots can use a rough three nautical miles per 1,000 feet of descent as an early jet-energy check, then refine it with aircraft-specific data and extra distance for slowing down.
A short-notice diversion often leaves the aircraft high and close to the airport. Extending the route or requesting vectors is usually safer than forcing an unstable descent. Before flying an unfamiliar procedure, verify its altitudes, minimums and missed approach using our practical explanation of how to interpret an instrument approach chart.
Common diversion mistakes
Most diversion errors come from delaying the decision, choosing the closest airport without checking it, or becoming absorbed in navigation-system programming.
| Mistake | Why it fails | Correction |
|---|---|---|
| Continuing towards a deteriorating destination | Fuel and airport options disappear while the crew waits for improvement. | Set clear decision points and divert before the reserve becomes the plan. |
| Selecting the first airport on the nearest list | The runway, weather, terrain or approach may be unsuitable. | Compare at least the hard safety requirements before committing. |
| Both pilots working heads-down | Flight-path, traffic and weather monitoring are lost. | Assign one pilot to fly and one to plan and programme. |
| FMS route not matching the clearance | The autopilot can accurately fly the wrong route. | Read back the clearance and verify the active legs against it. |
| Using optimistic fuel figures | Extra track miles, wind, vectors and a missed approach are omitted. | Recalculate from actual fuel and monitor predicted landing fuel repeatedly. |
| Briefing after descent has started | The crew reaches the approach without a shared plan. | Slow down, use vectors or extend the route to create preparation time. |
Simulator diversion practice
Diversions are best practised in a flight simulator by introducing one realistic reason to change destination and flying the complete decision, communication, reprogramming and landing sequence. Useful scenarios include destination weather falling below minima, a runway closure, an aircraft failure restricting approach choice, unexpected fuel loss or a passenger medical problem.
Begin with the simulator paused while learning the workflow, then repeat in real time without pausing or using an external map to rescue poor planning. Record the fuel at the decision and landing, how long the choice took, whether the FMS matched the intended route and whether the approach met normal stabilisation criteria.
Simulator scenery, procedure data and real-world charts may represent different dates, so a runway or waypoint can be present in one source and absent from another. Our guide to checking and updating flight simulator navigation data covers this common cause of failed diversion routes.