Plan an option that remains usable

Why is the nearest runway not always a useful alternate?

Availability, weather, performance and navigation must coincide at the relevant time.

Define a usable option

A candidate alternate needs an adequate runway, required facilities and services, compatible approach capability and acceptable expected conditions under the applicable planning criteria. Opening hours, rescue category, runway condition, wind and aircraft performance can reject a geographically close aerodrome.

Planning minima generally include defined allowances above operating minima under the applicable scheme. Do not substitute a current observation for the required forecast-window assessment, and do not reuse one synthetic margin for every approach type or operational approval.

Calculate a connected diversion

Use the specified missed approach at destination, climb, route to alternate, descent and approach/landing, including expected winds and restrictions. A shorter alternate can need more fuel if it requires an unfavourable level, strong headwind or long instrument routing. Compare suitable options using complete profiles.

Where more than one alternate is required, follow the applicable fuel-selection rule and planning criteria. The lesson’s synthetic comparison supplies independent candidate profile burns and suitability flags; it does not decide which regulatory requirement applies to a real operation.

Evaluate dependence and timing

Two options may share the same weather front, navigation outage or operating-hour restriction. A plan is stronger when the reasons that could remove an option are understood before departure. An alternate that is usable at its initially planned ETA may need reassessment after delay.

In the laboratory, a candidate marked unsuitable is rejected before comparing fuel cost. That ordering matters: a fuel-efficient route to an unusable aerodrome is not an operational option. The numerical fuel comparison then makes sense only among candidates that satisfy the stated suitability conditions and the governing requirements.

Why can an isolated destination change the meaning of a decision point?

Beyond a defined commitment point, a practical diversion may no longer remain available.

Protect a deliberate commitment

An isolated-aerodrome plan is a specific operational procedure, not permission to omit an alternate because it is inconvenient. The applicable scheme defines when it can be used, required weather and facilities, additional fuel and the point-of-no-return decision structure. Verify the current requirements and approved method.

Before crossing the defined commitment point, reassess destination conditions, aircraft status and predicted fuel. A deteriorating destination can require diverting while a suitable option still exists. Waiting until the fuel no longer supports that option defeats the purpose of the decision point.

Compare the required branches

A useful numerical teaching model calculates both the destination branch and a safe diversion branch from a common point, including their stated protected quantities. The larger requirement sets the point fuel requirement under this supplied model. The actual isolated procedure can contain specific allowances and inclusion rules that must be taken from its current source.

If a supplied isolated allowance says that it includes final reserve, do not add final reserve to it a second time. Read the reference condition, such as normal cruise or holding, before converting a duration into mass.

Understand what the model does not certify

The laboratory lets a student compare two explicitly synthetic branch requirements. It demonstrates a commitment decision and a maximum-of-requirements calculation, rather than implementing the full EASA isolated-aerodrome fuel scheme. Its numbers must not be used to release an isolated operation.

A real calculation also needs a valid route, suitable conditions over the required time window, approved performance data, communication and operational control provisions where applicable. A large extra fuel number does not by itself make an isolated destination suitable. State which future options remain available before and after the commitment point.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.