Avoiding Deadlocks Is Not Enough: Analysis and Resolution of Blocked Airplanes

TL;DR

This paper analyzes a transient blocking phenomenon in two-aircraft encounters, develops a mathematical model, and proposes an intention-aware, decentralized resolution strategy to prevent prolonged parallel flights and reduce collision risks.

Contribution

It introduces a novel analysis of blocking mode in airplane encounters, differentiates it from deadlocks, and presents a decentralized resolution strategy with adaptive priorities.

Findings

Blocking occurs under less restrictive conditions than deadlock.

The proposed strategy effectively resolves blocking without central coordination.

Simulations validate the analytical model and strategy effectiveness.

Abstract

This paper is devoted to the analysis and resolution of a pathological phenomenon in airplane encounters called blocking mode. As autonomy in airplane systems increases, a pathological phenomenon can be observed in two-aircraft encounter scenarios, where airplanes stick together and fly in parallel for an extended period. This parallel flight results in a temporary blocking that significantly delays progress. In contrast to widely studied deadlocks in multi-robot systems, such transient blocking is often overlooked in existing literature. Since such prolonged parallel flying places high-speed airplanes at elevated risks of near-miss collisions, encounter conflicts must be resolved as quickly as possible in the context of aviation. We develop a mathematical model for a two-airplane encounter system that replicates this blocking phenomenon. Using this model, we analyze the conditions under which blocking occurs, quantify the duration of the blocking period, and demonstrate that the blocking condition is significantly less restrictive than that of deadlock. Based on these analytical insights, we propose an intention-aware strategy with an adaptive priority mechanism that enables efficient resolution of ongoing blocking phenomena while also incidentally eliminating deadlocks. Notably, the developed strategy does not rely on central coordination and communications that can be unreliable in harsh situations. The analytical findings and the proposed resolution strategy are validated through extensive simulations.