The Tokyo Haneda runway collision was a classic runway incursion chain. A Japan Airlines A350 landed while a Japan Coast Guard Dash 8 was on the runway. The two aircraft collided and both caught fire. Early investigative material released to the public makes clear the smaller aircraft entered the runway without proper clearance and that tower personnel and the arriving crew did not detect the incursion in time to avoid impact.
A lot of readers ask whether airborne collision avoidance systems like TCAS could or should have warned the A350 crew and thus “bypassed” the ground safety breakdown. That is an understandable question from a pilot perspective. But the mechanics and design logic of TCAS make it the wrong tool for this problem.
TCAS II is an air to air system. It looks for other transponder equipped aircraft and issues traffic advisories and, when criteria are met, resolution advisories. Crucially, TCAS incorporates logic to determine whether a target is on the ground and to inhibit RAs near the ground. In the current widely used versions a number of protections are in place to avoid spurious or dangerous commands during landing and taxi phases. For example TCAS switches to a lower sensitivity level when the own aircraft is below about 1,000 feet AGL which inhibits RAs and limits advisories to TAs only. The logic also treats targets it estimates to be on the ground as non threats and will not generate vertical RAs for them. Those design choices are deliberate because RAs at or near the ground can create the very hazard the system is trying to prevent.
Put bluntly, in a touchdown scenario an arriving transport at landing speed is exactly the flight phase where TCAS is least likely to generate an RA against a runway vehicle or stopped aircraft. If the intruder is judged to be on the ground or the own ship is below the RA enable threshold, TCAS will not command an aggressive climb or descent. That is not a failure. It is a safety trade off baked into the system so crews are not given vertical escape commands that could cause controlled flight into terrain, collision with other traffic, or loss of control close to the ground.
The practical implication is simple. Preventing runway incursions is primarily a ground system and human factors problem. Surface surveillance, aural runway occupancy alerts in the tower, unambiguous stop bar lighting, robust ATC procedures, disciplined phraseology, and clear pilot readbacks are what stop an aircraft from being on the wrong runway at the wrong time. The public material around the Haneda event indicates a runway-occupancy warning was recorded by a support system but not effectively noticed in the tower and that certain stop bar lights were out of service under a NOTAM. Those are the kinds of ground side failures that TCAS was not designed to mitigate.
Operational takeaway for crews and operators: do not assume TCAS will be your runway safety net. During approach and landing keep sterile visual scan discipline, crosscheck the assigned runway and lights, call out anomalies as early as possible, and if something looks wrong reject the landing. From an industry perspective, airports and ANSPs need audible, unambiguous runway occupancy alerts and procedures that force immediate action when an alert is triggered. Until ground surveillance and human factors are improved, the risk remains that a fast landing on a night runway can meet an unexpected object and escape both human and airborne electronic detection.
Finally, note that the investigation into the Haneda collision was ongoing and led by Japan’s transport safety authority with international technical assistance cited in public reporting. As of now no public report attributes the accident to any TCAS malfunction or to an intentional bypass of airborne collision avoidance logic. The technical and procedural lessons to prevent a recurrence remain squarely focused on ground surveillance, tower procedures, pilot scanning and unambiguous communications.