Lois Larson
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 should have planned for and filed an alternate. According to FAR 91.169, commonly known as the 1, 2, 3 rule, you need to file an alternate 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, is forecast to have a ceiling of less than 2,000 feet or visibility of less than 3 statute miles, you are required to file an alternate. Additionally, the destination airport must have at least one instrument approach procedure, or an alternate airport will always be required.
| Characteristics | Values |
|---|---|
| When to file an alternate airport regulation | When the weather conditions forecast for the destination and first alternate airport are marginal, at least one additional alternate must be designated. |
| Weather conditions for not filing an alternate airport | If the weather at the destination, for at least 1 hour before and 1 hour after the ETA, is forecast to have at least a 2,000-foot ceiling and visibility of at least 3 statute miles, you are not required to list an alternate airport in the IFR flight plan. |
| Weather conditions for filing an alternate airport | 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. |
| Destination airport requirements | The destination airport must have at least one instrument approach procedure or an alternate airport will always be required. |
| Ceiling and visibility requirements | If a usable precision approach is available: 600 ft ceilings and 2 SM of visibility. If only a non-precision approach is usable: 800 ft and 2 SM of visibility. |
| No instrument approaches available | Descent from the MEA and landing must be conducted under basic VFR. |
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What You'll Learn
Weather conditions
Firstly, it is important to understand the concept of the "1, 2, 3" or "3-2-1" rule. This rule states that if the weather at the destination airport is forecast to have at least a 2,000-foot ceiling (above the airport elevation) and visibility of at least 3 statute miles for one hour before and after the estimated time of arrival, you are not required to list an alternate airport in the IFR flight plan. In simpler terms, if the weather conditions are good and meet these minimum requirements, an alternate airport filing is not necessary.
However, if either the ceiling height drops below 2,000 feet or the visibility falls below 3 statute miles during that arrival window, you are then required to file an alternate airport. This is because, in such conditions, the destination airport may not be safe or suitable for landing, and an alternative with better visibility and ceiling height is needed.
When considering weather conditions, it is important to analyze overall trends and not just rely on a single forecast. Examining a series of reports can provide a more accurate picture of the weather situation. Additionally, factors such as fuel requirements and mechanical issues should also be considered when planning for an alternate airport, as they can impact your ability to reach the alternate destination.
In some cases, an airport may not be available as an alternate due to a lack of weather reporting capabilities or unmonitored approach equipment. This is particularly true for smaller airports. Therefore, it is crucial to refer to the Terminal Aerodrome Forecast (TAF) or, in its absence, the Graphical Area Forecast (GFA) to determine the weather conditions at your potential alternate destinations.
Ultimately, while weather is a significant factor, alternate planning should not be based solely on weather conditions. Other factors, such as personal minimums, terrain considerations, and aircraft approach capabilities should also be taken into account to ensure a safe and feasible diversion plan.
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Instrument approach procedure
An instrument approach procedure (IAP) is a series of predetermined manoeuvres that pilots use to navigate an aircraft using flight instruments. These procedures are designed to provide specified protection from obstacles from the initial approach fix or, where applicable, from the beginning of a defined arrival route to a point from which a landing can be completed.
There are three categories of instrument approach procedures: precision approach (PA), approach with vertical guidance (APV), and non-precision approach (NPA). Each category has different requirements and capabilities. For example, a precision approach uses a navigation system that provides course and glide path guidance, while a non-precision approach uses a navigation system for course deviation but does not provide glide path information.
IAP charts are aeronautical charts that provide the aeronautical data required to execute an instrument approach to an airport. These charts depict topographic features, hazards, obstructions, procedures, and airport diagrams. Each procedure chart uses a specific type of electronic navigation system, such as NDB, TACAN, VOR, ILS/MLS, or RNAV. The charts also include important information such as minimum, maximum, and mandatory altitudes, as well as the minimum safe altitude (MSA) for emergencies.
When determining whether an alternate airport is required due to poor weather conditions, pilots can use the Terminal Aerodrome Forecast (TAF) or, in its absence, the Graphical Area Forecast (GFA). By using the "Ceiling/Visibility" tab and the Zulu time sliding bar, pilots can assess the weather conditions around their arrival airport and determine if an alternate airport is necessary.
In summary, instrument approach procedures are essential for pilots to safely navigate and land aircraft, especially in poor weather conditions. By using IAP charts and assessing weather forecasts, pilots can make informed decisions about their flight path and choose alternate airports if needed.
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Visibility
To ensure safe operations, regulations have been established to guide pilots in making informed decisions. According to FAR 91.169, if the weather conditions at the destination airport are predicted to be below certain visibility minimums, an alternate airport must be listed in the flight plan. Specifically, if the visibility is forecast to be less than 3 statute miles during the hour before and after the estimated time of arrival, an alternate airport is required.
These visibility minimums can vary depending on the availability of instrument approaches at the airport. If a usable precision approach is available, a visibility of 2 statute miles is required. In the absence of a precision approach, a non-precision approach may be used, but the visibility minimum increases to 2 statute miles. If no instrument approaches are available, descent and landing must be conducted under basic VFR, which typically requires better visibility conditions.
It is important to note that not all airports are suitable as alternates. Airports without weather reporting capabilities or with unmonitored approach equipment may not be used as alternates. Additionally, factors such as the number of runways, approach options, and circling minimums should be considered when evaluating potential alternate airports.
While regulations provide a framework, pilots must also exercise good judgment. Real-time weather information and access to nearby airports offer pilots more options and the ability to make informed decisions. However, it is crucial to always have a “Plan B” and be prepared to divert to an alternate airport if necessary.
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Ceiling height
When it comes to filing an alternate airport regulation, ceiling height is a crucial factor. The regulations specify the minimum ceiling height requirements that must be met for an airport to be considered a valid alternate.
According to the 3-2-1 rule (also known as the 1-2-3 rule), if the weather at the destination airport is forecast to have a ceiling height of at least 2,000 feet and visibility of at least 3 statute miles for one hour before and after the estimated time of arrival, you are not required to list an alternate airport. In other words, if the ceiling height is predicted to be below 2,000 feet during that arrival window, you must file an alternate.
When considering an alternate airport, it is important to analyze the overall weather trends in the area. The FAA has set standard alternate minimums, which state that an IFR alternate airport must be forecasted to have a ceiling height of at least 600 feet and visibility of 2 statute miles for a precision approach. For non-precision approaches, the requirements are slightly higher, with a minimum ceiling height of 800 feet and 2 statute miles of visibility. These standard minimums provide a buffer to ensure that the alternate airport does not have worse weather conditions than the original destination.
In certain cases, non-standard alternate minimums may apply, which can vary from approach to approach. For example, some airports may have specific requirements listed in the instrument approach procedure charts. It is important to refer to the published instrument approaches available at the alternate airport to determine if there are any non-standard minimums that need to be met.
Additionally, it is worth noting that some smaller airports may not have TAF reporting capability, so you would need to use the Graphical Area Forecast (GFA) to determine the weather conditions, including ceiling height and visibility.
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Fuel availability
Firstly, regulations require pilots to file an alternate airport and ensure they have sufficient fuel. This is a crucial safety consideration. In the past, pilots had limited access to real-time weather information, but now, with near-real-time weather data available via datalink, pilots can make more informed decisions and have a better chance of reaching their alternate airport without running out of fuel.
When planning a flight, pilots should always factor in their personal minimums and comfort levels. If a pilot is not comfortable flying in low-fuel conditions or adverse weather that could impact fuel efficiency, they should plan for a suitable alternative airport. This proactive planning helps ensure adequate fuel reserves and a safe landing.
Pilots should also be mindful of the potential need to declare an emergency landing due to low fuel. Failing to exercise "good judgment" in such situations could result in a violation of aviation regulations. Therefore, it is essential to continuously monitor fuel levels and be prepared to adjust plans accordingly.
Additionally, when considering alternate airports, it is worth noting that airports with a single runway, one approach, and no circling minimums in isolated areas may not be ideal. These airports offer fewer options and could increase the risk of fuel exhaustion.
Lastly, while filing an alternate airport is essential, pilots should also be practical. If the destination airport becomes unviable due to weather or other factors, pilots can slow down to save fuel and explore more suitable alternatives beyond the legal alternate. This flexibility ensures that pilots can make informed choices to find the best airport for a safe landing, considering factors such as fuel efficiency and overall flight conditions.
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Frequently asked questions
You need to file an alternate airport regulation 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.
The weather conditions required for filing an alternate airport regulation are a ceiling of at least 600' and 2 SM of visibility for usable precision approach, and 800' and 2 SM of visibility for non-precision approaches.
If you didn't file an alternate and the weather is bad but still within legal limits, you are most likely safe and legal to continue without naming an alternate. However, it is always recommended to name an alternate airport whenever possible.
When choosing an alternate airport, you should consider the overall weather trends in the area and select an airport with improving weather conditions. You should also factor in your personal minimums and ensure that the alternate airport meets the legal requirements.
Yes, according to § 91.169 (b), you do not need to file an alternate airport if the airport has an instrument approach procedure and appropriate weather reports indicating a ceiling of at least 2,000' and visibility of at least 3 SM for 1 hour before and after your ETA.
