What are weather minima for alternates?

Weather minima for alternates are the minimum forecast weather conditions (visibility and cloud base) required at an alternate aerodrome to ensure a safe landing if diversion is necessary.

Which documents provide weather information for alternate airport weather minima?

Terminal Aerodrome Forecasts (TAFs) and METARs are used to assess whether alternate airport weather minima are met during the relevant time window.

How is the time window for assessing alternate minima determined?

The required weather minima must be met for the period spanning the estimated time of arrival (ETA) at the alternate aerodrome plus and minus one hour.

Who sets the weather minima for alternates?

Weather minima for alternates are established by the operator and approved by the relevant aviation authority, in compliance with EASA regulations.

What happens if no alternate meets the required weather minima?

If no alternate meets the required minima, the flight cannot be dispatched until a suitable alternate is found or the weather improves.

Weather Minima for Alternates

Medium4 min readFlightplanning

Rarely Examined

Why this matters

Ensuring that an alternate airport meets weather minima is vital for flight safety, as it guarantees a viable diversion option in poor weather or emergencies. This decision directly impacts route planning, fuel calculation, and overall operational safety.

Weather minima for alternates are the minimum weather conditions that must be forecast or reported at an alternate airport to legally and safely nominate it in your flight plan. These minima ensure that, should a diversion be necessary, the alternate aerodrome will be usable for a safe approach and landing at the expected arrival time, considering both actual and forecast weather.

Quick Check

When planning a flight, for which period must the weather at alternate aerodromes meet the required minima?

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Explanation

Understanding Weather Minima for Alternates

When planning a flight, pilots must check the weather minima alternates—meaning the lowest acceptable weather conditions (visibility, cloud base, etc.) at any airport nominated as an alternate. These minima are based on the approach procedures available at the alternate and are set by the operator, in compliance with EASA alternate minima regulations.

Key Weather Information

Use both METARs (actual reports) and TAFs (forecasts) for the alternate airport weather minima assessment.
The critical period is ETA (Estimated Time of Arrival) at the alternate, plus or minus one hour.
The alternate airport weather requirements must be met for this entire window, not just at a single moment.

Calculation and Application

The required minima depend on the type of approach available (precision, non-precision, or circling) and may be higher than the published minima to account for forecast uncertainty.
If the forecast or actual weather is below these minima, the airport cannot be used as an alternate.
Always cross-check the latest weather data and ensure it covers the correct timeframe for your planned arrival at the alternate.

Practical Considerations

Weather minima for alternates aviation regulations are designed to ensure a safe landing option if the destination becomes unavailable.
Operators may set higher minima than the regulatory minimum, and these must be used in planning.
The process is critical for fuel planning, as the ability to use an alternate affects how much contingency and alternate fuel you must carry.

The essentials

Key Points

Weather minima for alternates are based on the approach type and operator-approved limits.

Assess both METAR (actual) and TAF (forecast) for the alternate airport.

The relevant period is ETA at the alternate plus or minus one hour.

Minima must be met for the entire ETA ±1 hour window, not just at a single time.

If weather is below minima, the airport cannot be used as an alternate.

Operator minima may be stricter than published aerodrome minima.

Correct alternate selection affects fuel planning and legal compliance.

Watch out

Exam Traps & Typical Mistakes

Only checking weather at the alternate for ETA, not ETA ±1 hour.

Using published minima instead of operator-approved minima.

Forgetting to consider both forecast and actual weather reports.

Assuming minima for one approach type when only another is available.

Ignoring stricter operator or regulatory requirements in favour of basic published values.

Test yourself

Example Exam Questions

Question 2Easy

Which weather report is primarily used to determine if an alternate aerodrome meets the required weather minima during flight planning?

Question 3Medium

If the operator's approved minima for an alternate require a visibility of 1500 m and a ceiling of 600 ft, but the TAF forecasts 1200 m visibility and 500 ft ceiling at ETA, what is the correct action?

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