Choosing Alternate Airports: When And Why You Need One

When planning a flight, it is important to consider whether you need an alternate airport. This decision is influenced by various factors, including the weather conditions and the availability of suitable airports. According to regulations, an alternate airport must be named on your IFR flight plan if, one hour before and after your estimated arrival time, the weather is forecast to include a ceiling of 2,000 feet and/or visibilities of less than three statute miles. This is known as the 1-2-3 rule. It is crucial to assess the field and determine the best area to choose an alternate airport, considering factors such as weather forecasts, instrument approach procedures, and standard or non-standard alternate minimums. These regulations ensure that pilots have a reliable Plan B and do not put themselves in unsafe situations.

When is an alternate airport required?

An alternate airport is always required, except when the following conditions are met:

Firstly, the airport must have an instrument approach procedure. This means that the ceiling—the maximum height of the base of the lowest layer of clouds—will be at least 2,000 feet above the airport elevation, and the visibility will be at least three statute miles. This is known as the 1-2-3 rule. For helicopters, the ceiling must be at least 1,000 feet above the airport elevation, or at least 400 feet above the lowest applicable approach minima, whichever is higher, and the visibility must be at least two statute miles.

Secondly, appropriate weather reports or forecasts, or a combination of them, must indicate that these conditions will be met for at least one hour before and one hour after the estimated time of arrival.

If these conditions are not met, then an alternate airport must be named on your IFR flight plan. This alternate airport must be forecasting weather with ceilings at or above 600 feet and two-mile visibility if it is served by a precision approach. If it only has non-precision approaches, then 800-foot ceilings and two-mile visibilities are required.

How to choose an alternate airport?

Choosing an alternate airport is a crucial aspect of flight planning, ensuring that pilots have a backup option if their intended destination becomes inaccessible due to unfavourable weather conditions or other unforeseen circumstances. Here are some detailed, instructive guidelines on how to select an alternate airport:

• Assess the Field and Weather Conditions: Before selecting an alternate airport, it is essential to evaluate the weather trends and forecasts for both the original destination and potential alternates. Consider the likelihood of thunderstorms, fog, or other weather systems affecting visibility and ceiling heights. Use weather reports and forecasts, such as METAR, TAF, or the Graphical Area Forecast (GFA), to make an informed decision.
• Distance and Fuel Requirements: Choosing an alternate airport that is too close to your original destination may not provide much benefit in terms of improved weather conditions. On the other hand, selecting an airport that is too far away can increase fuel requirements significantly. Opt for an airport with favourable weather conditions that comfortably allows for a diversion, keeping in mind the fuel needed to reach your alternate and execute an approach.
• Approach Types and Compatibility: Consider the types of approaches available at potential alternate airports. Determine if they align with the forecasted winds, or if circling-to-land manoeuvres will be necessary. Airports with only non-precision approaches, especially in low Instrument Meteorological Conditions (IMC), can make diversions more challenging.
• Non-standard Alternate Minimums: Verify if the potential alternate airport has non-standard alternate minimums. These airports may have specific requirements or restrictions due to factors like terrain elevation or the closure of certain runways or instrument approaches. Ensure that the forecasted weather conditions will allow you to legally file the airport as an alternate.
• Services and Accommodations: Choose an alternate airport that can provide necessary services and accommodations. Consider factors such as reliable weather reporting, fuel availability, hangar space, and hotels or accommodations for unexpected layovers. A towered airport with an ATIS broadcast and a 24-hour Fixed-Base Operator (FBO) can be advantageous.
• Legal and Regulatory Compliance: Familiarize yourself with the legal requirements for selecting an alternate airport, as outlined in regulations such as FAR 91.169. Ensure that your chosen alternate airport meets the necessary weather minima, including ceiling heights and visibility standards, for precision and non-precision approaches.

Remember, choosing an alternate airport is not just a legal requirement but also a practical measure to ensure the safety and success of your flight. Always give careful consideration to the specific circumstances of your flight, including aircraft capabilities, fuel requirements, and your personal minimums.

What are the regulations for an alternate airport?

An alternate airport is a backup airport in case your destination airport doesn't work out. For instance, if the weather deteriorates during your approach to the point where you can't see the runway, you need to plan for and file an alternate airport.

Regulations for an alternate airport

• The 1-2-3 rule: You need to file an alternate airport if the weather at the destination, for at least 1 hour before and 1 hour after the estimated time of arrival, is forecast to have less than a 2,000-foot ceiling (above the airport elevation) and visibility of less than 3 statute miles. If either the ceiling or visibility is forecast to be less than 2,000 feet or 3 statute miles during that arrival window, you are required to file an alternate airport.
• Destination airport: The destination airport must have at least one instrument approach procedure or an alternate airport will always be required.
• IFR flight plan: Unless otherwise authorized by ATC, each person filing an IFR flight plan must include an alternate airport.
• Weather conditions: No person may include an alternate airport in an IFR flight plan unless appropriate weather reports or forecasts indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima:

• Precision approach: If an instrument approach procedure has been published, or a special instrument approach procedure has been issued by the Administrator for that airport, the following minima must be met:
• For aircraft other than helicopters: A ceiling of 600 feet and visibility of 2 statute miles.
• For helicopters: A ceiling of 200 feet above the minimum for the approach to be flown, and visibility of at least 1 statute mile but never less than the minimum visibility for the approach.
• Non-precision approach: If no instrument approach procedure has been published, and no special instrument approach procedure has been issued by the Administrator for the alternate airport, the ceiling must be 800 feet and visibility must be 2 statute miles.
• No instrument approaches available: If no instrument approaches are available, descent from the MEA, approach, and landing must be conducted under basic VFR.

Fuel requirements: No person may operate an aircraft in IFR conditions unless it carries enough fuel to complete the flight to the first airport of intended landing, fly from that airport to the alternate airport, and fly after that for 45 minutes at normal cruising speed. Helicopters must have enough fuel to fly for 30 minutes at normal cruising speed.

What are standard and non-standard alternate minimums?

When filing an IFR flight plan, it is important to determine whether an alternate airport is required. An alternate airport is necessary when the weather conditions at the destination airport, from one hour before to one hour after your arrival time, are forecast to be below 2,000 feet AGL and/or have a visibility of less than three statute miles. This is known as the "1-2-3 rule".

When choosing an alternate airport, it is crucial to ensure that the weather conditions at the estimated time of arrival meet specific criteria. These criteria are known as alternate minimums and are classified into two types: standard and non-standard.

Standard Alternate Minimums:

Standard alternate minimums are the basic requirements for an alternate airport. They dictate that the forecasted conditions at the time of arrival must be at least two miles of visibility and a ceiling of at least 600 feet for precision approaches or 800 feet for non-precision approaches. These requirements ensure that pilots have a safe and reliable "Plan B" if they cannot land at their original destination due to unfavourable weather conditions.

Non-Standard Alternate Minimums:

Non-standard alternate minimums are adjusted requirements that supersede the standard minimums for specific airports or approaches. They are indicated by an inverted triangle with an "A" on an approach plate. Non-standard minimums are typically implemented for safety reasons and can vary from approach to approach. For example, some approaches may not be available when the control tower is closed, or the minimum visibility or ceiling requirements may be adjusted.

To find the non-standard alternate minimums for a particular airport or approach, pilots can refer to the front section of the Terminal Procedures Publication or use tools like ForeFlight, which provides detailed information about alternate airports and their respective requirements.

In conclusion, understanding standard and non-standard alternate minimums is crucial for safe IFR flight planning. By considering these requirements, pilots can ensure they have a reliable "plan B" and make informed decisions about their alternate airports and approaches.

Practical suggestions for choosing an alternate airport

When choosing an alternate airport, it is important to consider a range of factors to ensure a safe flight. Here are some practical suggestions to help you make an informed decision:

• Weather conditions: Consider the weather at both your destination and potential alternate airports. Check forecasts and weather trends to assess the likelihood of diverting due to unfavourable weather. The "1-2-3 rule" is a common guideline, which states that if, one hour before and after your estimated time of arrival, the ceiling is forecast to be at least 2,000 feet and visibility is at least three statute miles, you may not need to list an alternate airport. However, if the weather is predicted to be worse than these minimums, choosing an alternate airport is necessary.
• Distance: Avoid selecting an alternate airport that is too close to your original destination, as the weather conditions may not be significantly different. On the other hand, choosing an airport that is too far away can increase fuel requirements and pose other challenges.
• Approaches available: Consider the types of approaches available at the alternate airport. If only non-precision approaches are available, especially in low IMC conditions, your diversion may be more challenging.
• Non-standard alternate minimums: Verify if the airport has non-standard alternate minimums, as this may impact the forecasted weather conditions required to legally file the airport as an alternate. Consider the reasons for non-standard minimums, such as nearby terrain that could influence weather conditions.
• Services available: Choose an alternate airport with reliable weather reporting and the necessary services you may require, such as fuel availability and hangar space. Consider selecting a towered airport with an ATIS broadcast and a 24-hour FBO.
• Fuel requirements: Ensure you have enough fuel to reach your alternate airport and fly an approach. Consider the fuel requirements for your specific aircraft and the payload you are carrying.
• Tools and resources: Utilise tools such as ForeFlight or Garmin Pilot, which offer alternate airport planning features and provide key information like forecast weather, runway length, and fuel requirements. Additionally, refer to weather resources like the Terminal Aerodrome Forecast (TAF) or the Graphical Area Forecast (GFA) to make informed decisions.

Remember, choosing an alternate airport is an important aspect of flight planning and should be given careful consideration. Always prioritise safety and adhere to regulations when making your decision.

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