General Manager, Butler Avionics
ADS-B and TCAS II are often mentioned in the same breath, but they are not the same system and one does not replace the other. TCAS II actively prevents collisions by interrogating the transponders of nearby aircraft and issuing resolution advisories. ADS-B enriches the crew’s traffic picture through broadcast position data. Installed together, they give a flight crew both a dedicated collision avoidance layer and a broader, earlier view of the traffic environment.
What Is the Difference Between ADS-B Out and ADS-B In?
ADS-B Out broadcasts an aircraft’s GPS derived position, altitude, and velocity to ground stations and to other nearby aircraft, once per second. It is a one way transmission: the aircraft is telling the airspace around it where it is. ADS-B In is the receiving half. An aircraft equipped with ADS-B In picks up broadcast position data from other ADS-B equipped traffic, along with ADS-B rebroadcast data and traffic information service broadcasts relayed by ground stations, and displays that traffic picture directly to the flight crew.
In U.S. airspace, ADS-B operates on two frequencies: 1090 MHz Extended Squitter and 978 MHz Universal Access Transceiver (UAT). A dual link receiver can pick up traffic on both, which matters because the aircraft around you may be equipped for either one depending on where and how high they fly.
How Do ADS-B and TCAS II Work Together?
It helps to be precise about what each system is actually doing, because they solve related but distinct problems. TCAS II is an active system. It interrogates the transponders of nearby aircraft directly, independent of whether those aircraft are broadcasting ADS-B data at all, and uses the responses to compute range, altitude, and closure rate. When a conflict develops, TCAS II issues a resolution advisory instructing the crew to climb or descend. This works regardless of ADS-B equipage on the other aircraft, which is exactly why TCAS II remains the primary collision avoidance layer rather than a supplement to ADS-B.
ADS-B, by contrast, is a broadcast and receive system. It does not interrogate anything, and it does not issue resolution advisories. What it does is significantly enrich the traffic picture a crew sees on their cockpit display, including aircraft and data sources that TCAS II’s active interrogation may present less completely, along with additional context like ground based traffic relayed through TIS-B for aircraft that are not directly ADS-B equipped.
The practical result is a layered system rather than a single point of protection. TCAS II is doing the safety critical interrogation and advisory work. ADS-B is giving the crew a broader, earlier, and more complete situational picture of the traffic environment around them.
Is an ADS-B Equipped Aircraft Protected by TCAS II?
No, and this is one of the most common points of confusion. ADS-B Out is primarily a surveillance requirement: it makes an aircraft visible to air traffic control and to other ADS-B In equipped aircraft. Meeting that requirement does not add collision avoidance logic or resolution advisories to the cockpit. An aircraft can be fully ADS-B compliant and still have no TCAS II protection at all.
The reverse is also true. TCAS II on its own does not provide the broadcast weather, TIS-B traffic, or the wider air to air picture that ADS-B In delivers. That is why the two are best understood as separate but complementary capabilities, and why operators evaluating one should also look at the status of the other.
What Should Operators Consider When Planning an Upgrade?
Every combined ADS-B and TCAS II installation starts with the existing aircraft. The current transponder, GPS position source, and cockpit displays all shape what the integration looks like, and a thorough panel review up front prevents surprises during installation. Operating profile matters as well: aircraft that fly above 18,000 feet or outside U.S. airspace need 1090 MHz Extended Squitter ADS-B Out, while UAT based ADS-B Out is limited to operations below 18,000 feet in the U.S.
Display integration is the next consideration. ADS-B In data is only as useful as the crew’s ability to see it, so the plan should account for how traffic and weather will reach compatible cockpit displays and, where appropriate, portable devices through a wireless gateway.
Finally, operators should pay attention to hardware lifecycle. Avionics manufacturers regularly discontinue and replace units, and the datalink hardware at the center of the ADS-B function is
What Does the Upgrade Process Involve?
For an eligible Learjet 31 or 31A, the process starts with confirming the aircraft against the STC and reviewing the existing panel to plan the integration of all three components. From there, Butler handles parts sourcing and in house installation, using the same certified process whether the aircraft is getting the original GDL-88 or the updated replacement datalink unit. That consistency means the ADS-B and TCAS II functionality delivered to the aircraft is the same either way, even as the specific hardware generation changes.
Why Does This Matter for Operators?
For owners and operators, combining ADS-B and TCAS II delivers both the active protection of a dedicated collision avoidance system and the enriched situational picture that ADS-B In provides. Treating them as a single, integrated upgrade rather than two unrelated projects reduces downtime, simplifies coordination, and results in a traffic picture the crew can trust.
Butler Avionics plans, sources, and installs integrated ADS-B and TCAS II systems in house, with a focus on safety, quality, and end-to-end support. Reach out to discuss your aircraft and start planning the work.
For owners and operators of the Learjet 31 and 31A, this upgrade delivers both the active protection of TCAS II and the enriched situational picture that ADS-B In provides, through a single certified path that Butler keeps current as the underlying components change. Reach out to confirm eligibility and start scheduling the work.
Frequently Asked Questions
Is ADS-B the same thing as TCAS II?
No. TCAS II provides active collision avoidance through transponder interrogation and resolution advisories, while ADS-B provides a broader traffic picture through broadcast data. They can be installed together, but they are not the same system.
Does ADS-B Out compliance give my aircraft collision avoidance?
No. ADS-B Out makes your aircraft visible to air traffic control and to other equipped aircraft. Collision avoidance with resolution advisories comes from TCAS II.
Why does a dual link ADS-B receiver matter?
Traffic in U.S. airspace may broadcast on either 1090 MHz or 978 MHz. A dual link receiver displays both, giving the crew a more complete picture of nearby ADS-B equipped aircraft.
What happens if a component in my system is discontinued?
Manufacturers typically introduce a replacement unit. A shop that follows OEM product changes can identify the current generation equivalent and plan the installation around hardware that remains supported.
Ready to talk through your options?
Whether you need a quick repair or it’s time for a full replacement, Butler Avionics can help you figure out the right path. As a global source for Learjet avionics, we offer FAA and EASA certified solutions with in-house installation available.
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