Owais Crawford
When it comes to flying, contingency planning is crucial. A flight might not go as expected due to mechanical failure, sickness, turbulence, or adverse weather conditions. In such cases, pilots must divert to an alternate airport. While filing a flight plan, pilots must select an alternate airport that meets specific legal requirements, primarily concerning weather conditions. This ensures that pilots have a Plan B and carry enough fuel to reach their alternate destination. However, pilots are not required to fly to their filed alternate and can choose any airport that meets the necessary legal criteria. This flexibility allows pilots to make informed decisions and divert to the most suitable airport when needed.
| Characteristics | Values |
|---|---|
| Definition | ICAO defines an alternate aerodrome as "an aerodrome to which an aircraft may proceed when it becomes either impossible or inadvisable to proceed to or to land at the aerodrome of intended landing where the necessary services and facilities are available, where aircraft performance requirements can be met and which is operational at the expected time of use" |
| Types | Take-off, En-route, Destination |
| Take-off alternate | An aerodrome where an aircraft can land shortly after take-off if it is not possible to use the departure aerodrome |
| En-route alternate | An aerodrome where an aircraft can land in the event a diversion is necessary while en route |
| Destination alternate | An aerodrome where an aircraft can land if it becomes impossible or inadvisable to land at the intended aerodrome |
| Requirements | Airports with weather reporting, monitored approach equipment, and fuel availability |
| Considerations | Proximity, weather conditions, personal minimums, and aircraft performance |
| Regulations | FAR 91.169 specifies the weather conditions and fuel requirements for filed alternate airports |
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What You'll Learn
Weather conditions
For airports with an instrument approach procedure, the ceiling must be 200 feet above the minimum for the approach, with a visibility range of at least 1 statute mile. In some cases, a circling instrument approach may not be authorized, in which case the ceiling requirements differ. The ceiling must be at least 1,500 feet above the lowest published minimum or 2,000 feet above the airport elevation, whichever is higher.
When determining alternate airports, pilots should analyze overall weather trends in the area and not simply choose the closest airport. It is important to consider if the weather is improving or worsening and plan accordingly. Personal minimums should also be factored in, as pilots may have individual comfort levels when it comes to flying in low-visibility conditions.
In addition to weather conditions, other factors come into play when selecting alternate airports. These include mechanical issues, sickness, turbulence, and destination abnormalities. Understanding these factors and planning for them can improve the effectiveness of the flight plan.
It is worth noting that some airports may not be available as alternates due to a lack of on-airport weather reporting capabilities or unmonitored approach equipment. Airports with a single runway, one approach, and no circling minimums in isolated areas may also be less desirable as alternates.
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Fuel requirements
When determining fuel requirements, it is important to consider weather reports, forecasts, and conditions. For aircraft other than helicopters, the FAA requires that, for at least 1 hour before and after the estimated time of arrival, the ceiling will be at least 2,000 feet above the airport elevation, and visibility will be at least 3 statute miles. Traditional area forecasts do not go below a 1,000-foot ceiling, so forecast IFR conditions at your destination with no TAF require an alternate.
In some cases, an alternate airport may not be required. If weather forecasts predict that a pilot can descend from the MEA in forecast VFR weather conditions, no alternate airport is needed. Additionally, if the airport of intended landing is forecasting "pretty good MVFR conditions" (the 1-2-3 guide), no alternate needs to be filed.
It is important to note that, even if an alternate airport is not required, it is always a good idea to have a \"Plan B\" in mind in case you need to divert. This way, you can avoid fumbling around the cockpit searching for nearby diversion options and instead have an easy go-to strategy. When choosing an alternate airport, it is recommended to plan a direct route and calculate your regular cruise fuel requirement. Additionally, consider adding a safety buffer of at least one extra hour in case your alternate airport is also unusable, even if it means adding a fuel stop to your flight plan.
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Pilot's decision
A pilot's decision on which airport to file as an alternate is a critical aspect of flight planning and is influenced by various factors, including weather conditions, airport suitability, and regulatory requirements. Here are some key considerations for pilots when making this decision:
Understanding the Regulatory Framework: Pilots must be familiar with the regulations governing alternate airports. The Federal Aviation Administration (FAA) in the United States, for example, requires the filing of an alternate airport for Instrument Flight Rules (IFR) planning. However, Visual Flight Rules (VFR) conditions may allow for exceptions. Understanding these regulations is essential for compliance and safety.
Weather Conditions and Forecasting: Weather plays a pivotal role in a pilot's decision. Airports with Terminal Aerodrome Forecasts (TAF) or other reliable weather reporting capabilities are preferred. Pilots should analyze overall weather trends and forecasts to assess conditions at potential alternate airports. In areas with limited forecasting tools, pilots may need to rely on Graphical Area Forecasts (GFA) or other approved methods to determine ceiling heights and visibility.
Suitability of Alternate Airports: When selecting an alternate airport, pilots should consider factors such as runway length, approach options, and the availability of necessary services and facilities. Some airports may have specific requirements, such as higher alternate minimums due to terrain considerations or equipment limitations. Airports without weather reporting capabilities or with unmonitored approach equipment are typically not suitable as alternates.
Proximity and Diversion Options: While proximity to the intended destination is a factor, it should not be the sole criterion. Pilots should consider the availability of airports in the vicinity, especially when flying over desolate or mountainous areas. Assessing practical diversion options ensures that pilots have viable alternatives if they need to divert from their planned route.
Fuel Considerations: Regulations mandate carrying enough fuel to reach the destination, the alternate airport, and have sufficient reserve for unforeseen circumstances. This fuel calculation is crucial in the pilot's decision-making process, as it ensures the aircraft can safely reach the alternate airport without compromising performance or violating fuel exhaustion protocols.
Personal Minimums and Prudent Decision-Making: Pilots should also consider their personal minimums and comfort levels. If a pilot is not comfortable flying into low-visibility conditions, they should plan for an alternative with better weather. Additionally, pilots must exercise good judgment and consider factors beyond just legal minimums, as outlined in FAA advisories.
By carefully evaluating these factors, pilots can make well-informed decisions about which airports to file as alternates, ensuring compliance with regulations, maintaining safety margins, and being prepared for unforeseen events during their flights.
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Aerodrome type
Alternate aerodromes are classified into three types: takeoff, en-route, and destination alternates. Takeoff alternates are aerodromes where an aircraft can land shortly after takeoff if it is impossible to use the departure aerodrome. En-route alternates are intended for diversions that become necessary while in transit. Destination alternates, on the other hand, are aerodromes where an aircraft can land if it becomes impossible or inadvisable to land at the intended aerodrome.
According to ICAO, an alternate aerodrome is "an aerodrome to which an aircraft may proceed when it becomes either impossible or inadvisable to proceed to or land at the aerodrome of intended landing, where the necessary services and facilities are available, where aircraft performance requirements can be met, and which is operational at the expected time of use."
When selecting an alternate aerodrome, it is important to consider the prevailing conditions and ensure they meet the applicable operating minima. Additionally, factors such as weather conditions, fuel availability, and the presence of instrument approaches should be taken into account.
In terms of practical considerations, it is worth noting that the filed alternate is not sent to air traffic control (ATC) and is instead kept in an FSS database. Therefore, if a diversion becomes necessary, ATC will need to be informed of the chosen alternate. While the choice of alternate airport is flexible and can be made based on real-time weather information, it is still crucial to have a well-thought-out "Plan B" before takeoff.
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Safety considerations
Safety is a critical aspect of aviation, and choosing an alternate airport is an important consideration in ensuring safe operations. Here are some detailed safety considerations regarding alternate airports:
Weather Conditions:
When selecting an alternate airport, weather conditions play a crucial role. Pilots should refer to accurate and up-to-date weather forecasts to make informed decisions. In the United States, the Federal Aviation Administration (FAA) requires access to "appropriate weather reports and forecasts, or a combination of them" for naming destinations and determining alternates. This includes information about cloud ceiling height and visibility. If the destination airport is predicted to have marginal weather conditions, at least one additional alternate airport should be designated.
Instrument Approach and Navigation:
The availability of instrument approach procedures and navigation aids is essential for alternate airports. Airports without weather reporting capabilities or with unmonitored approach equipment cannot be used as alternates. The use of GPS and WAAS-capable navigators provides additional flexibility in alternate planning, allowing for RNAV approaches at both the destination and the alternate airport. However, it is important to be cautious when solely relying on information streamed to cockpits, as real-time weather information may change rapidly.
Aerodrome Operating Minima:
Alternate aerodromes must meet applicable operating minima regarding weather conditions and available facilities. This includes ensuring that the aerodrome is operational at the expected time of use and can accommodate the aircraft's performance requirements. The specific minima will depend on factors such as the number of engines and the aircraft's mass.
Fuel Considerations:
Regulations require carrying enough fuel to fly to the destination, the alternate airport, and then have sufficient fuel for 45 minutes at a normal cruise speed. This ensures that pilots have adequate fuel reserves in case they need to divert to the alternate airport.
Take-off and En-route Alternates:
In specific circumstances, take-off and en-route alternate aerodromes may be necessary. A take-off alternate is crucial if an aircraft needs to land shortly after departure and cannot return to the departure airport. An en-route alternate is designated when a diversion becomes necessary during the journey. These alternates ensure safety during different phases of the flight.
The "3 Rs" Rule:
Instructors often advise flight students to consider the "3 Rs" rule when selecting an alternate airport. This rule suggests choosing an alternate with Radar coverage, a Restaurant, and Rental Cars, in addition to the legal weather requirements. This ensures not only safety but also a level of comfort and convenience for both pilots and passengers.
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Frequently asked questions
A legal alternate airport is an airport that meets the legal requirements for a pilot to begin an approach to landing. This is determined by weather reports or forecasts, and other criteria such as terrain considerations and aircraft approach category.
It is important to have a "Plan B" in case you need to divert from your original flight plan. This could be due to various reasons such as mechanical failure, sickness, weather conditions, or destination abnormalities. Filing an alternate airport ensures you have a backup option and carry adequate fuel.
When choosing an alternate airport, it is crucial to consider the weather conditions and overall trends in the nearby area. Analyze multiple weather reports and forecasts to determine the best option. Additionally, consider the airport's infrastructure and your aircraft's capabilities. Ensure the airport meets the legal requirements and suits your specific needs.
