What is ALT1 in Aviation? (Alternate)

In aviation, the term “Alternate” refers to an alternative airport that serves as a backup to the primary destination airport in case of unforeseen circumstances. ALT1 is the abbreviation used to denote the alternate airport in the flight planning and aviation communication systems. It is crucial for pilots and air traffic controllers to have a clear understanding of the concept of alternates and their significance in ensuring the safety and efficiency of flights.

When planning a flight, pilots must consider the possibility of changing weather conditions, equipment malfunctions, or any other factors that might render the primary airport unsuitable for landing or takeoff. In such situations, having a designated alternate airport becomes vital to provide a reliable destination for the aircraft, ensuring the well-being of the passengers and crew on board.

Importance of Alternate Airports

The selection of an alternate airport is based on various factors, including the aircraft’s range, fuel capacity, weather conditions, runway length, and availability of navigation aids. It is essential to choose an alternate airport that is within the aircraft’s fuel range and can accommodate its size and weight. Additionally, the chosen alternate should have suitable weather conditions, such as visibility and wind limits, to allow for a safe landing.

Alternate airports play a critical role in enhancing the safety of aviation operations. Having a backup destination provides pilots with a viable option during emergencies, diversions, or in situations where the primary airport is congested or temporarily closed. This allows for better flight planning, reduces the chances of unplanned delays, and ensures the continuous flow of air traffic.

When selecting an alternate airport, pilots must consider its location in relation to the primary destination airport. It should be within a reasonable distance, allowing for sufficient fuel reserves in case of diversion. Additionally, the alternate airport should have adequate ground support facilities, including runway maintenance equipment, firefighting services, and passenger handling capabilities.

It is important to note that the selection of alternate airports is not a one-size-fits-all approach. Each flight has its own unique requirements and constraints, and the choice of alternate should be specific to the aircraft, route, and prevailing conditions. Aviation authorities, such as the International Civil Aviation Organization (ICAO), provide guidelines and recommendations to assist pilots and operators in the selection and use of alternates.

Factors Considered for Alternate Selection

Several factors come into play when pilots and air traffic controllers determine the most suitable alternate airport for a particular flight. These factors are essential to ensure the availability of a reliable option in critical situations. Let’s explore some of these key considerations:

1. Weather

Weather conditions play a crucial role in the selection of alternate airports. Pilots assess the current and forecasted weather conditions at the primary destination airport and potential alternates. They consider factors such as visibility, wind speeds, cloud cover, and precipitation to determine the suitability of a particular airport for landing. The chosen alternate should have weather conditions within acceptable limits to allow for a safe approach and landing.

The availability of weather information plays a significant role in alternate airport selection. Pilots can access real-time weather data from meteorological stations, air traffic control, or aviation weather services. This data helps them evaluate the weather conditions en route and at potential alternate airports, enabling them to make informed decisions regarding the choice of an alternate.

2. Runway Length and Surface

The length and surface of the runway at an alternate airport are crucial factors to consider. Aircraft have different runway length requirements based on their size, weight, and performance capabilities. Pilots must ensure that the selected alternate airport has a runway long enough to accommodate the aircraft’s takeoff and landing performance.

Additionally, the runway surface must be suitable for the aircraft’s landing gear and braking system. Runways with poor surface conditions, such as excessive roughness or inadequate friction, can pose safety risks during landing or takeoff. Pilots must assess the runway condition and surface type (e.g., paved, grass, gravel) to determine the feasibility of using the alternate airport.

3. Navigation Aids and Approach Procedures

Alternate airports must have adequate navigation aids and approach procedures to allow for instrument-based approaches in adverse weather conditions. These aids, such as Instrument Landing Systems (ILS), VHF Omnidirectional Range (VOR), and Global Positioning System (GPS), assist pilots in accurately navigating and aligning the aircraft during the approach and landing phases.

The availability and reliability of these navigation aids at alternate airports are critical factors in their selection. Pilots need to ensure that the chosen alternate has functioning and certified navigation equipment to support safe instrument approaches, especially in low visibility conditions.

Moreover, pilots should consider the availability of published approach charts and minimum descent altitudes for the alternate airport. These charts provide detailed information on various instrument approach procedures, enabling pilots to execute safe approaches and landings.


Alternate airports are an integral part of aviation operations, providing a backup destination in case of unforeseen circumstances. Pilots carefully consider various factors such as weather, runway length, navigation aids, and approach procedures when selecting an alternate airport. By having a designated alternate, pilots ensure the safety, efficiency, and continuity of flights, minimizing the impact of any disruptions on passengers, crew, and the overall air traffic system.

For More: What is VDP in Aviation? (Visual Descent Point)