FASST-CH encompasses the entire airspace. However, the proposed e-conspicuity mandate is focused on airspace class E, considering that 1) class C/D are already well covered by Air Traffic Service (ATS) and 2) the number of manned flights flying exclusively in Class G is close to 0.
1. Is the scope of the FASST-CH initiative limited to airspace class E or is it comprising all airspace (including G)?
2. How does the FASST-CH project use the term ADS-L in the context of FASST-CH?
3. Why is there no technology recommendation for portable ADS-B out devices ?
4. I already have a Mode S transponder. Why should I use ADS-B or ADS-L?
5. I already have a Mode S transponder. Is it possible to obtain special financing for the upgrade to ADS-B out?
6. How can I install external antennas for ADS-L / ADS-B or how do I upgrade to ADS-B out or install a traffic warning system? How much work is involved?
7. What should a pilot-in-command (PIC) consider when using ADS-L on a tablet?
8. What traffic information can I receive with ADS-L?
9. What is the performance of my transmitter?
10. What is antenna diversity and why is it important?
11. Why is FOCA recommending the ADS-L protocol, and how does this align with EASA?
12. ADS-L devices will not be certified. Are there nevertheless recommendations or at least expectations regarding the performance of these devices?
13. What is the difference between ADS-B and ADS-L?
14. How are UAS covered in FASST-CH?
15. Are these technology recommendations future proof?
16. Will my ADS-L device warn me of all (100 %) traffic and what does this mean for the see-and-avoid principle under VFR or IFR?
ADS-L is generally defined by EASA’s technical specifications.
ADS-L “out” is simply a beacon function to transmit an aircraft’s position on the SRD 860 band.
ADS-L “in” is the function to receive other aircraft positions on the SRD 860 band. However, ADS-L devices usually have dual or triple band receivers, for SRD 860, ADS-B 1090 MHz and sometimes UAT 978 MHz.
ICAO is working on the development of standards for "Reduced Performance Devices" operating on the 1090 MHz frequency. These standards would aim to balance the need for situational awareness provided by low-power ADS-B devices with the imperative to maintain the integrity and performance of existing surveillance systems.
Once this work is completed, the technology recommendation will be updated accordingly.
The mandate for Mode S transponders (without ADS-B out) for motor-powered aircraft ensures protection for commercial air traffic via TCAS. This is especially important in CTRs, TMAs and areas where commercial IFR aircraft transit through airspace class E. This mitigation of high severity risks is the reason why Mode S transponders remain a valuable piece of equipment.
However, Mode S transponders without ADS-B out are interrogation dependent. This means that without an interrogation by a ground radar or a TCAS, the transponder will remain silent and is therefore sometimes electronically “invisible” to other GA users. Furthermore, a Mode S transponder, if interrogated only in A/C mode, will reply in the same mode. Some GA users might have traffic warning systems, which only sense Mode S and not Mode A/C (see STSB report nr. 2406).
In contrast, ADS-B and ADS-L broadcast their data automatically at frequent intervals. Therefore, these types of transmitters remain electronically visible to other GA users continuously, even in the absence of interrogations from ground radars or TCAS.
An application for financial support can be submitted to the Special Financing of Civil Aviation (BV87b)). Financial support for e-conspicuity devices and for Upgrading from Mode S to ADS B out is available under this framework.
The installation of antennas, an upgrade to ADS-B out or installation of a traffic warning system can be done with a standard change under CS-STAN or with a supplemental type certificate (STC). This applies to both EASA and non-EASA (annex I) aircraft.
The required work hours for installation depends on the individual aircraft. An antenna installation with diversity (one antenna at the top and one below the airframe) in the best-case scenario takes about 3 hours to complete. In the worst case it could also take multiple days to install. Please contact the avionics maintenance organisation for specific cases.
To integrate a traffic warning system into existing avionics, an installation takes about a full day of work. This can vary, in case the panel is difficult to access and other factors.
The pilot in command of a non-complex aircraft under Part-NCO is solely responsible for using a personal electronic device (PED), including an electronic flight bag (EFB) running an ADS-L application. Commission Regulation (EU) No 965/2012 of 5 October 2012 laying down technical requirements and administrative procedures related to air operations contains more information in article NCO.GEN.125 and its acceptable means of compliance and guidance material.
Human factors are crucial in the use of a tablet (electronic flight bag, EFB). It could easily distract the PIC from other tasks, such as a consistent, continuous visual lookout. Studies have shown that a traffic alert can increase the likelihood of visually acquiring traffic by eight times. A recent study conducted by the UK CAA also showed that an alert by an EFB can lead the pilot to abandon the traffic scan and only focus on a single traffic alert, shifting focus between the EFB and the assumed location in the windscreen. This can increase collision risk with more relevant, closer and electronically invisible traffic. Pilots are urged to continue their visual scan for traffic, even when a traffic alert is given by the EFB, especially when traffic is further away than 2 NM (beyond this distance, the human eye can only detect traffic in ideal conditions).
Further information: New study on Electronic Conspicuity published by aviation regulator | UK Civil Aviation Authority
Traffic information on an EFB can help to strategically avoid "hot spot” areas. It is not meant to be used for tactical avoidance like TCAS, where the avionics issue an action to climb or descend. Strategic avoidance, in contrast, enables the PIC to amend the flight path prior to even getting close to others. For example, the PIC might see multiple gliders or paragliders soaring on one side of a valley. With this traffic information on the tablet, the pilot can decide early, to fly a different route or altitude.
It is recommended to use audio alerts via the intercom or a bluetooth headset, rather than flying “head down”, looking at the EFB. It is essential to keep looking outside and maintain a wide visual traffic scan even if getting a traffic alert!
ADS-L devices are generally multi-mode receivers. They can receive air-to-air traffic data from aircraft equipped with ADS-B and ADS-L. With some devices, the pilot can receive bearingless traffic information about traffic with transponders replying to interrogations in mode C or Mode S (*).
When within the area of a ground antenna with ADS-L SRD 860 traffic uplink, the device may also receive rebroadcasted traffic data. This functionality is linked to the implementation of the FASST-CH ecosystem. More information on the plan and progress of this implementation will be provided in due time on the FOCA FASST-CH web page.
Please consult with the manufacturer to get a complete and up to date view of the capabilities of your device.
(*) The aircraft’s transponder reply mode depends on the interrogation mode of the ground radar or TCAS. Transponder signals can be made electronically visible via multilateration (MLAT) and uplinked via an ADS-L ground antenna. However, in the absence of an interrogation from a ground radar or TCAS, transponders without ADS-B (Mode S and mode C) are not electronically visible.
It is important to check if the system performs as expected. It is possible to test the performance of the transmission signal on the ground or in the air. Detailed information on how to do this in the scope of FASST-CH will follow.
There are multiple antenna options to be considered:
- Device antenna: An antenna directly attached to or within a portable device is a convenient solution but sometimes placed in suboptimal locations. Follow the manufacturer guidance for best placement. The sender’s signal may be almost completely blocked in some directions due to the airframe or other factors.
- Remote antenna: With an extension cable, the remote antenna can be placed in better locations within the cabin.
- External antenna: With one or two external antennas, the signal strength can in many cases be further improved.
Antenna diversity is usually accomplished by connecting more than one antenna to the same transponder. The goal is to reduce signal obstruction by the airframe. This is an important factor in both permanently installed ADS-B and non-certified ADS-L solutions.
Traditionally, transponder antennas have been installed below the fuselage. This ensures reception of the signal on the ground for secondary surveillance radar (SSR). This is suitable for the air-ground use case of SSR. In the scope of the air-to-air use case (to be electronically visible to other aircraft), this is a limitation due to signal obstruction by the airframe. It is ideal to install antennas not only below, but also on top of the fuselage. This is called antenna diversity.
For general aviation aircraft there are also other options available to achieve vastly improved antenna diversity. One example is a dipole antenna integrated into a taillight, which broadcasts both towards the sky and towards the ground. The main advantage of such installations is the lower installation cost, which is supporting the FASST-CH objective to provide fit for purpose affordable solutions to all types of airspace users.
ADS-L is the solution promoted by EASA to make General Aviation Airspace Users electronically visible. The FASST-CH project is aligned with the EASA to ensure seamless flying throughout Europe.
Manufacturers are encouraged to follow best practices and provide instructions for the adequate installation and use of devices, even for uncertified ones. Particularly, the installation of conspicuity devices (or/and its antenna) in an area free from obscuration and in a direct line of sight with surrounding airspace is key for performance. Pilots are encouraged to strictly follow the manufacturer’s instructions for the adequate installation, use and maintenance of the devices.
ADS-B and ADS-L are different e-conspicuity protocols operating at different frequencies.
ADS-B (Automatic Dependent Surveillance–Broadcast) is a certified surveillance technology used primarily in controlled airspace using an aviation protected frequency band (1090 MHz) for real time tracking by air traffic control and other aircraft.
ADS-L (Automatic Dependent Surveillance–Light), on the other hand, is a non-certified, lower-cost alternative intended mainly for electronic conspicuity to improve situational awareness. ADS-L operates on a non-protected frequency band (SRD 860). While it performs a similar function — broadcasting position information — it operates with limited regulatory oversight, making it suitable for general aviation and recreational flying.
FASST-CH focuses on making manned flights visible to each other and to relevant stakeholders. UAS will benefit from this visibility to ensure they remain well clear from manned traffic.
The intention of the FASST-CH project is to recommend technologies which are considered future proof. This is, for example, clearly the case for certified ADS-B out in motor-powered aircraft. On the other hand, the use of smart, affordable, noncertified devices contributes to achieve a net-safety benefit and solve the interoperability issue existing today.
The performance of noncertified devices is not as predictable as would be the case with certified equipment. It cannot be ruled out that during the trial phase of FASST-CH, some portable devices would not perform as initially expected. For example, if the FOCA repeatedly identifies an extremely low range of a certain device, the recommendation can be amended accordingly (e.g. recommend the device for use only in certain aircraft categories or recommend adding external antennas).
This openminded approach is an inherent attribute of FASST-CH and is unique for a project of a civil aviation authority. In 2028, when the e-conspicuity mandate is planned to enter into force (depending on the rulemaking process and stakeholder involvement), the FOCA should have the needed data to assess if certain e-conspicuity devices or installations would not meet the required performance.
Today, ADS-L devices warn the pilot of all traffic using the same protocol (e.g. FLARM, PilotAware); in the future they will warn about all traffic equipped with ADS-L. In case the device is a dual band receiver (SRD 860 + 1090 MHz), the pilot will see ADS-B and Mode S equipped traffic as well.
The objective of FASST-CH is to ensure that every device will warn the pilot of all the surrounding traffic. This will be achieved by following two steps:
- From 2028 on, all traffic will be equipped with either ADS-L or ADS-B / Mode S
- A ground infrastructure will gather data of all conspicuous traffic and rebroadcast e-conspicuity signals.
The following table summarizes what each type of device might be able to warn of, this table is for information purposes only, and you should always check the supplier provided information:
In Out |
Dual Band ADS-L & ADS-B receiver (*) |
Single Band ADS-L receiver |
Single Band ADS-B receiver (*) |
|---|---|---|---|
ADS-L out |
Yes |
Yes |
Ground to Air |
ADS-B out / Mode S |
Yes |
Ground to Air |
Yes |
Proprietary (+) |
Yes if same brand |
Yes if same brand |
No (**) |
(*) An ADS-B receiver is assumed to be receiving as well Mode S signals from surrounding traffic having been interrogated either by a ground radar or an airborne ACAS.
(+) Proprietary refers to existing devices operated on SRD 860 (e.g. FLARM, PilotAware)
(**) It is not envisaged to rebroadcast signals other than ADS-L and ADS-B / Mode S
It is important to remember that even without 100% electronic visibility, these devices contribute to the increase of situational awareness and complement the visual acquisition of traffic.
See and avoid remains fully applicable as per:
- ICAO Annex 2 Chapter 3.2.2 that requires pilots to "maintain vigilance so as to see and avoid other aircraft", and
- Commission Implementing Regulation (EU) 923/2012 (SERA – Standardised European Rules of the Air Regulation), Section 3, Chapter 2 (e.g. SERA.3205) that provides detailed rules on which aircraft has the right-of-way, and reinforces the obligation of seeing and avoiding other traffic.
For a refresher on see-and-avoid best practices, the AC 90-48E - Pilots’ Role in Collision Avoidance and EGAST Leaflet GA 1 Collision Avoidance are interesting reads.
Other frequently asked questions on this topic are available on the EASA website (in English):
Last modification 27.05.2025
