Situational Awareness and Technology including FLARM

The CAA’s Class G for the 21st Century Airspace study recognises that the level of risk in class G is acceptable. Statistics demonstrate that the greatest collision risk to gliders are other gliders, and the greatest collision risk to aeroplanes are other aeroplanes. Most collisions occur close to airfields.

Situational awareness, in very simple terms, is a pilots awareness of what is going on around him or her (the CAA’s CAP737 provides detail from p77). Pre-flight planning, thinking ahead whilst airborne, and staying aware of the immediate surrounds by looking for and detecting potential airborne conflicts all contributes to situational awareness.

Lookout is the primary method of collision avoidance in class G airspace. All pilots have a responsibility to ensure that they can maintain effective lookout.

Some pilots choose to use technology to enhance their awareness. Some of that technology is described below.

Please note that it is necessary to avoid any in-cockpit equipment from distracting from the visual lookout scan.


Most glider pilots fly in radio equipped gliders. Correctly used, radio is helpful in building and maintaining situational awareness, including with air traffic controllers. Pre-programming frequencies before flight can prevent head down time and other in-flight hazards caused by distraction. Information about pilot radio licences can be found here.

Use of Traffic and Collision Warning Systems

The BGA encourages the widespread use of traffic and collision warning systems in gliders, motor gliders and tugs.

Pilots should make their own decision on equipage based on compatibility with other systems and as to whether such a system is appropriate for their particular operation. Pilots are reminded that whilst electronic collision warning equipment can enhance pilots’ awareness by providing most useful warnings, such equipment cannot and must not replace a good systematic visual lookout scan.


FLARM is an increasingly popular system and particularly so within gliding.

Each FLARM device determines its position and altitude with a highly sensitive state of the art GPS receiver. Based on speed, acceleration, heading, track, turn radius, wind, altitude, vertical speed, configured aircraft type, and other parameters, a very precise projected flight path can be calculated. The flight path is encoded and sent over an encrypted radio channel to all nearby aircraft at least once per second.

At the same time, the FLARM device receives the same encoded flight path from all surrounding aircraft. Using a combination of own and received flight paths, an intelligent motion prediction algorithm calculates a collision risk for each received aircraft based on an integrated risk model. The FLARM device communicates this, together with the direction and altitude difference to the intruding aircraft, to the connected FLARM display. The pilots are then given visual and aural warnings and can take resolutive action.

There is evidence that some FLARM aerial installations are nowhere near as effective as they could be. We advise owners check their FLARM coverage using the FLARM online tool. The tool is available on the FLARM website here. For LXNAV 9000, 8000, 8080 and Flarm mouse, the tool is here.

You can read more about FLARM technology here.

FLARM has published guidance on aerial installation. You can view it here.

Learn about checking and improving FLARM coverage here.

Other FLARM maintenance guidance is available here.

Other Technology


A transponder provides a signal that is externally interrogated. Depending on the type of interrogation, a transponder sends back a ‘squawk code (Mode A) and/or altitude information (Mode C) to help air traffic controllers to identify the aircraft and to maintain separation. Another mode called Mode S (Mode Select) is designed to help avoiding over-interrogation of the transponder (eg many radars in busy areas) and to allow collision avoidance with similarly equipped aircraft. Mode S transponders are ‘backwards compatible’ with Modes A & C. Transponders represent very limited benefit to the users in uncontrolled airspace. Power use is an issue for any aircraft reliant on battery power.


Automatic dependent surveillance – broadcast (ADS–B) is a cooperative surveillance technology in which an aircraft determines its position via satellite navigation and periodically broadcasts it, enabling it to be tracked. The information can be received by ATC ground stations as a replacement for secondary radar. It can also be received by other aircraft to provide situational awareness and allow self separation.

ADS–B is “automatic” in that it requires no pilot or external input. It is “dependent” in that it depends on data from the aircraft’s navigation system. ADS-B data can be recorded and downloaded for post-flight analysis. ADS-B also provides the data infrastructure for inexpensive flight tracking.

The system relies on two components—a high-integrity GPS navigation source and a datalink (ADS-B unit). There are several types of certified ADS-B data links, but the most common ones operate at 1090 MHz. To obtain ADS-B Out capability at 1090 MHz, one can install a new transponder or modify an existing transponder plus install a certified GPS position source if one is not already present.

The Future Airspace VFR Implementation Group (FASVIG), which is supported by the BGA, is working on a variety of future airspace issues including those relating to ADS-B and associated component and certification issues. If you want learn more, please take a look at the FASVIG website.