"Very different" version of civil system provides last-minute automatic avoidance
An automatic collision avoidance system (ACAS) that would provide protection against mid-air collisions between combat aircraft, as well as allow integration of manned and unmanned aircraft in close proximity, has been declared feasible following tests by the US Air Force.
Proof-of-concept tests of Auto ACAS were conducted using an aircraft provided by Eglin AFB, Florida, and were co-sponsored by the Swedish government and the USAF Research Laboratory. Although using similar transponder and interrogation technology to the commercial traffic alerting and collision avoidance system (TCAS), the USAF test team says Auto ACAS is "very different" from its civil counterpart because it provides last-minute, automatic avoidance rather than early deconfliction.
Tests were conducted using a standard Lockheed Martin F-16CG, the Edwards AFB-based VISTA NF-16D and a third "virtual" F-16 for co-operative and non-co-operative test runs. Over 32 flights, 43 sorties and 72 flight hours, the test team accomplished 343 "successful" simulated collision runs from 586 attempts. Some 38% of the collision runs involving two real aircraft were effective, compared with 59% when a virtual aircraft was involved.
The tests were aimed at proving the viability of an ACAS that automatically took control from the pilot when the system sensed the presence of an intruder within an "uncertainty" cone, and that a collision was imminent. It was then programmed to safely manoeuvre the aircraft away from the threat and immediately return control to the pilot. The USAF believes the system would be a great potential aid to reducing the number of mid-air collisions, of which there were 41 between 1993 and 2002, leading to 89 fatalities. The technology is also vital for the future use of unmanned air vehicles in national US airspace and within mixed formations with manned aircraft, says the air force.
The team says test pilots "never aimed for a head-on collision, but always for at least a 200ft [60m] offset", and were warned of the danger by the closure of chevrons that appeared on the head-up display. The results indicated the system always prevented a collision, but not always with the 200ft-plus buffer, and mostly with about 100ft to spare. It also gave control back to pilots in dangerous or exposed moments such as "inverted, and 30-40° nose down in some cases", says the test team, which "recommended that an operational system recover to a safer level hand-off".
Source: Flight International
