Roberta Aguirre
When selecting an alternate airport, pilots must consider the available instrument approach procedures (IAPs) and ensure that they meet the required navigation performance (RNP). RNAV approaches, which utilize GPS/WAAS, offer operational flexibility and are listed with various approach minimums to accommodate different aircraft capabilities. Standard alternate minimums for non-precision RNAV approaches include a ceiling of at least 800 feet and a visibility of two statute miles, but exceptions exist. When planning for an alternate airport, pilots must consider the availability of IAPs other than GPS, as well as the aircraft's equipment and capability to navigate using these approaches. WAAS-equipped aircraft, for instance, can utilize RNAV (GPS) LNAV or circling minima at the alternate airport. Ultimately, while flight planning is crucial, pilots can also coordinate with air traffic control (ATC) to divert to a suitable alternate airport if needed.
| Characteristics | Values |
|---|---|
| Alternate airport considerations | Any required alternate airport must have an available instrument approach procedure (IAP) that does not rely on GPS. |
| GPS-based IAP | GPS users with specific equipment and training may file based on a GPS-based IAP at either the destination or the alternate airport, but not both. |
| Standard alternate minimums | A ceiling of at least 800 feet and a visibility of two statute miles. |
| Non-standard alternate minimums | Some airports may require a forecast of higher ceilings and/or visibility. Refer to the chart for the planned instrument approach for a black triangle with the letter A. |
| RNAV approaches | Utilize GPS/WAAS with varying precision and minimums. Include LNAV, LP, LNAV/VNAV, and LPV. |
| WAAS receivers | Users with WAAS receivers may flight plan to use any IAP authorized for their avionics at the alternate airport with certain restrictions. |
| Practical considerations | If your original destination only has RNAV approaches, your alternate airport must have an approved non-GPS instrument approach procedure available at the estimated time of arrival. |
| RNP 0.3 DA on RNAV (RNP) IAP | Requires authorized users with approved baro-VNAV equipment and verified RNP availability through a prediction program. |
| Avionics considerations | The first generation of IFR-approach GPS receivers were approved for LNAV-only approaches and require verification of RAIM availability. |
| LNAV/VNAV decision altitude | Aircraft with GPS and approach-certified baro-VNAV can achieve LNAV/VNAV decision altitude. |
| Operational flexibility | RNAV approaches list multiple minimums to ensure aircraft can fly the approach even if WAAS is unavailable. |
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What You'll Learn
Alternate airport planning policy
Alternate airport planning policies have evolved over the years, with the Federal Aviation Administration (FAA) issuing updates to its policies. The use of GPS-based Instrument Approach Procedures (IAPs) for alternate airport calculations was previously restricted in many situations. However, in April 2013, the FAA issued a NOTAM on the "Alternate Airport Flight Planning Using GPS and Wide Area Augmentation System (WAAS) Policy Statement," allowing pilots more flexibility in their planning.
According to the current policies, pilots can plan to use a GPS-based IAP at either the destination or the alternate airport, but not at both locations. This means that if an aircraft is equipped with GPS and the pilot has the required knowledge and training, they can utilise a GPS-based approach at their alternate airport. This is a significant change from previous policies, which often prohibited the use of GPS-based approaches at alternate airports.
When selecting an alternate airport, pilots must ensure that it has an approved instrument approach procedure other than GPS that will be operational and available upon arrival. This restriction also applies to conducting a conventional approach at the alternate airport, where GPS-based equipment cannot be solely relied upon. Additionally, the use of WAAS at an alternate airport must comply with specific guidelines, including the use of RNAV (GPS) LNAV or circling minima lines, as outlined in the Code of Federal Regulation (CFR) Part 91 non-precision weather requirements.
It is important to note that alternate airports may have non-standard alternate minimums, requiring higher ceilings and visibility forecasts. These exceptions can be identified by referring to the chart for the planned instrument approach, where a black triangle with the letter A indicates non-standard minimums. When using RNAV approaches, pilots should refer to the standard alternate minimums of a ceiling of 800 feet and a visibility of two statute miles, unless otherwise specified.
To summarise, the alternate airport planning policy allows for the use of GPS-based IAPs at either the destination or the alternate airport, providing flexibility for pilots. However, it is crucial to ensure that the alternate airport has an approved instrument approach procedure other than GPS and that any GPS-based equipment is used in accordance with the regulations.
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GPS-based IAP at alternate airports
For a long time, pilots could not use a GPS-based Instrument Approach Procedure (IAP) as part of their alternate airport calculations. However, the Federal Aviation Administration (FAA) issued a Flight Data Center (FDC) NOTAM in 2013, which allowed pilots to use a GPS-based IAP at either the destination or the alternate airport, but not at both locations.
For GPS-based IAP at alternate airports, pilots may plan for applicable alternate airport weather minimums using the following:
- Lateral navigation (LNAV) or circling minimum descent altitude (MDA).
- LNAV/vertical navigation (LNAV/VNAV) decision altitude (DA) if equipped with and using approved barometric vertical navigation (baro-VNAV) equipment.
- RNP 0.3 DA on an RNAV (RNP) IAP, if they are specifically authorized users using approved baro-VNAV equipment and the pilot has verified required navigation performance (RNP) availability through an approved prediction program.
If the above conditions cannot be met, any required alternate airport must have an approved instrument approach procedure other than GPS that is anticipated to be operational and available at the estimated time of arrival, and which the aircraft is equipped to fly.
For GPS users with approved baro-VNAV capability, the current alternate airport planning policy prohibits them from planning to use WAAS vertical guidance at their alternate airport. However, they can plan to use the RNAV (GPS) LNAV minima line or the minima on a GPS approach procedure or conventional approach procedure with “… or GPS” in the title.
The standard alternate minimums for a non-precision approach (RNAV/GPS or VOR) are an 800-foot ceiling and 2-mile visibility. However, there are exceptions, and many airports have non-standard alternate minimums that may require a forecast of higher ceilings and/or higher visibility.
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Standard alternate minimums
It is important to note that not all airports adhere to these standard minimums. Many airports have non-standard alternate minimums, which may require a forecast of higher ceilings and/or visibility. To determine if an airport has non-standard minimums, pilots can refer to the chart for the planned instrument approach and look for a black triangle with the letter A. This symbol indicates that non-standard alternate minimums apply, and pilots will need to refer to the IFR Alternate Airport Minimums reference for the specific requirements.
When selecting an alternate airport, it is crucial to ensure that the airport has an approved instrument approach procedure other than GPS. This restriction includes conducting a conventional approach at the alternate airport using a substitute means of navigation based on GPS. For example, if the RNAV 32 approach at JXN airport looks like a viable option, a pilot can use the standard alternate minimums since there is no black A symbol on the chart. This means they can legally file JXN as an alternate, even if their planned arrival time is after the control tower's closing.
Additionally, pilots should consider the capabilities of their aircraft's GPS system. Older GPS receivers were only approved for LNAV-only approaches and required the pilot to verify receiver autonomous integrity monitoring (RAIM) during the approach. With these systems, pilots can only plan to fly an RNAV approach based on LNAV minimums at either the destination or alternate airport, not both. However, newer GPS navigators with WAAS capability offer more flexibility, allowing pilots to plan RNAV approaches at both the destination and the alternate airport.
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Non-standard alternate minimums
The standard alternate minimums for an airport to qualify as an alternate airport require a forecast of at least 2 miles visibility and at or above 600-foot ceilings for precision approaches, or 800-foot ceilings for non-precision approaches. However, some airports have non-standard alternate minimums that supersede these requirements. These non-standard minimums provide an extra layer of safety and may require a forecast of higher ceilings and/or higher visibility.
To determine if an airport has non-standard alternate minimums, pilots can refer to the chart for the planned instrument approach. A black triangle with the letter A indicates that non-standard alternate minimums apply, and pilots need to refer to the IFR Alternate Airport Minimums reference. If using paper charts, these can be found in the front of the approach chart book. ForeFlight users can navigate to the Airports screen, select the Procedures tab, select Arrival, and then Alternate Minimums.
For example, at Pellston, MI (PLN), if the only option is to fly the RNAV Rwy 5 approach due to strong winds, the forecast would need to be for 900-foot ceilings and 2 miles visibility for Category A and B speeds to file PLN as a legal alternate airport.
It is important to note that non-standard alternate minimums may apply to a specific approach at an airport, but not all approaches at that airport. Additionally, when planning a flight with RNAV approaches, pilots must assume they will be flying to the LNAV minimums, which are higher than LPV minimums, to build extra safety margins.
Furthermore, regulations state that any required alternate airport must have an approved instrument approach procedure other than GPS that is anticipated to be operational and available at the estimated time of arrival, and which the aircraft is equipped to fly. This ensures that pilots do not choose an alternate airport with potentially similar or worse weather conditions than the original destination.
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RNAV approaches
RNAV, or Area Navigation, is a way for pilots to navigate without needing ground-based navigation aids. RNAV approaches use GPS to help pilots land and offer more flexibility than traditional systems like ILS. They are especially useful for smaller airports or those without the budget or terrain to install an Instrument Landing System (ILS). RNAV approaches are now available at thousands of airports worldwide, making more airports accessible under Instrument Flight Rules (IFR).
When selecting an alternate airport, pilots must consider the availability of RNAV approaches. Any required alternate airport must have an approved instrument approach procedure other than GPS that is anticipated to be operational and available at the estimated time of arrival, and which the aircraft is equipped to fly. This restriction does not apply to WAAS users (TSO-C145() and TSO-C146() equipped users).
For GPS users, there are additional considerations when selecting an alternate airport. GPS users must have proper knowledge and any required training and/or approval to conduct a GPS-based IAP. They must also ensure that the conventional approach at the alternate airport can be flown without reliance on GPS.
When determining if an airport has the necessary RNAV capabilities, pilots can refer to the chart for the planned instrument approach. A black triangle with the letter A indicates that non-standard alternate minimums apply, which may require a forecast of higher ceilings and/or higher visibility. For example, at Pellston, MI (PLN), if the only option is to fly the RNAV Rwy 5 approach due to strong winds, a forecast of 900-foot ceilings and 2 miles visibility is needed to file PLN as a legal alternate airport.
Overall, RNAV approaches offer increased flexibility and accessibility for pilots and airports, but careful planning is required to ensure safe and successful flights.
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Frequently asked questions
The standard alternate minimums for an airport with a non-precision approach (RNAV/GPS or VOR) are a ceiling of at least 800 feet and a visibility of two statute miles.
For flight planning purposes, TSO-C129 and TSO-C196-equipped users (GPS users) who have the necessary knowledge and approval to conduct a GPS-based IAP may use GPS equipment at either the destination or the alternate airport, but not at both locations.
Any required alternate airport must have an approved instrument approach procedure other than GPS that is anticipated to be operational and available at the estimated time of arrival, and which the aircraft is equipped to fly.
