Sachin Walls
An alternate airport is a backup airport in case a pilot's original destination doesn't work out. This could be due to weather conditions or other factors. When deciding on an alternate airport, pilots must consider the overall weather trends in the area and the availability of instrument approaches at the airport. The Federal Aviation Regulations (FAR) 91.169 outlines the criteria for when an alternate airport must be filed in the flight plan, which is commonly known as the 1, 2, 3 rule. This rule states that if the weather at the destination, for one hour before and after the estimated time of arrival, is forecast to have at least a 2,000-foot ceiling and visibility of at least three statute miles, an alternate airport does not need to be listed. However, if either the ceiling height or visibility is expected to be less than these minimums, an alternate airport must be filed.
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What You'll Learn
Weather conditions
Firstly, it's important to understand the "1, 2, 3" rule, also known as the 3-2-1 rule. This rule states that you need to file an alternate airport if the weather at your destination is forecast to be below certain minimums during the critical period of one hour before and one hour after your estimated time of arrival (ETA). Specifically, if the ceiling is predicted to be less than 2,000 feet (above the airport elevation) or the visibility is expected to be less than 3 statute miles during this time frame, you are required to file an alternate airport.
Weather Reports and Forecasts:
When making the decision to file an alternate airport, always refer to the latest weather reports and forecasts. This information is crucial for determining if the weather conditions will meet the minimum requirements for landing at your destination. You can use tools like ADS-B datalink weather and local ATIS/AWOS radio broadcasts to stay updated on weather conditions near your destination.
Legal and Personal Minimums:
There are legal minimums set for weather conditions that must be met by the destination airport or an alternate airport. These legal alternate minimums are non-negotiable. However, it's also important to consider your personal minimums. If you feel uncomfortable flying in certain weather conditions, plan accordingly and choose an alternate airport that suits your comfort level.
Short Flights and Weather Trends:
On shorter flights, pay closer attention to weather reports rather than just forecasts. By examining a series of reports, you can identify trends and make a more informed decision. This is especially important when dealing with rapidly changing weather conditions.
Instrument Approach and Visibility:
Always consider the instrument approach procedure at your destination airport. If there is no instrument approach available, an alternate airport with an appropriate approach procedure is required. Additionally, be mindful of localized areas of low visibility, such as those caused by a passing cold front. Ensure that both your destination and alternate airports have the necessary approach capabilities to handle these conditions.
Fuel Considerations:
When planning for an alternate airport, remember to factor in the fuel requirements. Regulations, such as 14 CFR 91.167, mandate that you must carry enough fuel to fly to your destination, then to the alternate, and finally, have enough fuel for an additional 45 minutes at a normal cruise speed. These fuel considerations are crucial for ensuring the safety and feasibility of your flight plan.
In summary, when it comes to weather conditions and filing an alternate airport, always prioritize safety and adhere to legal requirements. Stay updated with weather reports and forecasts, consider your personal comfort levels, and ensure that your flight plan includes sufficient fuel for both your destination and the alternate airport.
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Instrument approach procedure
An alternate airport is a backup plan in case the 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, an alternate airport is required.
When it comes to filing an alternate airport, there are specific criteria and regulations that need to be considered. Firstly, it is important to understand the "1, 2, 3" rule. According to this rule, you need to file an alternate airport if the following conditions are met:
- If the weather at the destination, for at least 1 hour before and 1 hour after the estimated time of arrival (ETA), is forecast to have a ceiling of less than 2,000 feet (above the airport elevation) or visibility of less than 3 statute miles. In this case, an alternate airport with better weather conditions is required.
- The destination airport must have at least one instrument approach procedure. If the destination airport does not have an instrument approach procedure, an alternate airport with this capability is required.
When determining the alternate airport, it is important to analyze the overall weather trends in the area. The Graphical Area Forecast (GFA) can be used to assess the weather conditions, specifically the “Ceiling/Visibility” tab and the Zulu time sliding bar. Additionally, it is crucial to verify different factors before choosing an airport as an alternate, ensuring that it meets the necessary requirements.
While planning, it is essential to determine the time en route between your destination and the alternate airport to find the ETA for the alternate. To meet the requirements, the weather conditions at the ETA must meet or exceed specific standards:
- If a usable precision approach is available: 600-foot ceilings and 2 statute miles (SM) of visibility.
- If only a non-precision approach is usable: 800-foot ceilings and 2 SM of visibility.
- If no instrument approaches are available: Descent from the Minimum Enroute Altitude (MEA) and landing must be conducted under basic Visual Flight Rules (VFR).
It is important to note that some airports have non-standard alternate requirements due to terrain considerations, and these requirements may vary by aircraft approach category. Additionally, certain airports may have specific approach procedures that need to be considered when planning an alternate.
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Forecasts and current weather
When it comes to filing an alternate airport in your flight plan, taking into account the forecasts and current weather conditions is of utmost importance. Here's a detailed overview:
When considering an alternate airport, pilots must examine the weather forecasts and current conditions at both the destination and potential alternate airports. This involves studying the Terminal Area Forecasts (TAFs) and/or Area Forecast (FA) for the relevant airports. TAFs provide a detailed forecast of wind, visibility, and weather conditions expected at an airport during a specified period, typically covering a 24-hour period. FA, on the other hand, offers a broader view, providing a forecast for a larger area, which can be useful for understanding the overall weather pattern.
By analyzing these forecasts, pilots can anticipate any potential issues, such as low visibility due to fog or heavy precipitation, that might require a diversion to an alternate airport. It is crucial to review these forecasts right before filing the flight plan to have the most up-to-date information. Additionally, staying aware of any AIRMETs (Airmen's Meteorological Information) or SIGMETs (Significant Meteorological Information) is essential, as they provide critical information about weather phenomena that may affect the safety of flight operations.
Current weather conditions play an equally vital role in decision-making. Checking the METAR (Aviation Routine Weather Report) for the destination and alternate airports provides a snapshot of the present weather, including wind speed and direction, visibility, cloud cover, and any prevailing weather phenomena. Comparing the actual weather conditions with the forecasts helps in validating the forecasts' accuracy and identifying any unexpected changes. If the current weather conditions at the destination airport deteriorate beyond the required minima for the approach, a diversion to the alternate airport may be necessary.
In addition to the forecasts and current weather, understanding the trend and stability of the weather is crucial. For instance, if the weather is improving and stable, it may be safe to continue towards the destination airport. On the other hand, if the weather is deteriorating or unstable, diverting to an alternate airport may be a wiser choice. Staying updated with the latest weather information throughout the flight is essential, as conditions can change rapidly, and a timely decision to divert may become necessary.
Pilots should also be mindful of the weather conditions en route to the alternate airport. Ensuring that the chosen alternate airport is not experiencing similar adverse weather conditions as the destination airport is vital. This involves checking the forecasts and current weather for the alternate, as well as the weather along the route to ensure a safe and feasible diversion if needed.
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Visibility and ceiling
When deciding whether to file an alternate airport, pilots must consider the overall weather trends around their arrival. This includes checking the ceiling and visibility at the airport.
The ceiling refers to the height of the lowest layer of clouds above the ground. According to FAR 91.169, if the ceiling is below 2,000 feet, an alternate airport must be filed. This is known as the 1-2-3 rule, where the ceiling should be at least 2,000 feet, and visibility should be at least 3 statute miles for one hour before and after the ETA.
If a usable precision approach is available, the minimum requirements are a ceiling of 600 feet and 2 statute miles of visibility. If only a non-precision approach is usable, the requirements are 800 feet and 2 statute miles of visibility. In the case of no instrument approaches being available, descent and landing must be conducted under basic VFR, which means maintaining a ceiling of at least 1,000 feet and visibility of at least 1 statute mile.
It is important to note that weather conditions can change rapidly, and pilots should always have a "Plan B" in mind. When deciding on an alternate airport, pilots should consider the overall weather trends and not simply choose the closest airport. If the weather is predicted to deteriorate, selecting an alternate airport with improved weather conditions is advisable. Additionally, personal minimums should be considered, and if a pilot feels uncomfortable flying into low-weather conditions, they should plan an alternative route.
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Legal requirements
The Federal Aviation Administration (FAA) requires that an alternate airport be specified when filing an IFR flight plan. However, there are certain conditions under which this is not necessary.
Firstly, if the airport has an instrument approach procedure, and appropriate weather reports or forecasts indicate that, one hour before to one hour after your ETA, the ceiling will be at least 2,000' AGL, and the visibility will be at least 3 statute miles, then you do not need to file an alternate airport. This is often referred to as the 1-2-3 rule.
If the above conditions are not met, you are required to file an alternate airport. The weather conditions at the ETA of the alternate airport must meet or exceed certain minima, as outlined in FAR 91.169. These minima vary depending on the type of approach available:
- Usable Precision Approach: 600' ceilings and 2 statute miles of visibility
- Only Non-Precision Approaches Available: 800' and 2 statute miles of visibility
- No Instrument Approaches Available: Descent from the MEA and landing must be conducted under basic VFR
It is important to note that not all airports are eligible to be used as alternate airports. To determine eligibility, refer to the "`alternate minimums`" tab in the "arrival procedures" section when using ForeFlight. If an airport is not eligible, you will see an "NA" before the triangle with an "A" on the Notes section's approach plate.
Additionally, pilots must comply with the preflight action requirements outlined in FAR 91.103. This includes becoming familiar with all available information concerning the flight, including weather reports and forecasts, fuel requirements, alternatives if the planned flight cannot be completed, and any known traffic delays. While it is not required to officially declare an alternate airport when flying VFR, it is recommended to have a few airports in mind along the route and near the destination as a plan B.
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Frequently asked questions
An alternate airport is a backup airport in case your destination doesn’t work out, for instance, due to poor weather conditions.
You should file an alternate airport when 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.
You can use the Terminal Aerodrome Forecast (TAF) or the Graphical Area Forecast (GFA) to determine weather conditions around your arrival. You should always analyze the overall trends of nearby weather and plan for an alternate with better forecasts if the weather is predicted to get worse.
The minimum requirements for an alternate airport are a 600-800 foot ceiling and 2 statute miles of visibility, depending on the approach available.
You should also consider the availability of instrument approaches and your personal minimums. It is important to have a Plan B and choose an alternate airport that you are comfortable flying into.
