TIM ROBINSON reports as Europe's MIDCAS UAV demonstrator project wraps up a successful 'detect and avoid' flight-test campaign.

The flight trials used a modified Alenia Sky-Y UAV fitted with five different sensors. (EDA)

While in recent months much attention has been given to the future potential of small package UAVs operating in civil aerospace, the larger the UAV, the more important that it has a robust sense and avoid (or detect and avoid (D&A)) system in place. Currently, military UAVs are deconflicted carefully, either flying in empty ranges, conflict zones or under close supervision to operate under or thread between ATC-controlled civil air routes.

Yet as the potential of UAVs becomes more and more pent-up — so too are the rules becoming more restrictive. The ability to fly in controlled civil airspace would not only allow larger UAVs to fly cargo, patrol, communications relay, or search and rescue missions (to name but four) — but for military users would allow ferry flights, training missions and give a huge boost in operational flexibility. Notes the European Defence Agency (EDA): “There is an interest from the civil side, but the military have pressing need now, as the dominant user of large RPAS. We work closely with SESAR, and EASA recently issued their concept of operations for RPAS. A D&A system will almost certainly be a requirement for certain classes of RPAS.”

However, to fully unlock the skies the thorny and complex challenge of D&A must be addressed. Unlike the smaller, lighter quadcopters found under 500ft and operated within line of sight, a mid-air collision between a tactical or MALE-sized drone or larger (the Reaper UAV for example has a wingspan of 20m and a MTOW of 10,494lb) and a manned aircraft represents a whole different level of threat.


Inside the GCS (Ground Control Station) for the MIDCAS UAV demonstrator. (EDA)

To that end there are now several projects investigating and de-risking D&A for unmanned air vehicles to allow them to use controlled civil airspace on a regular basis. In the UK, this has been led by the ASTRAEA consortium - which has conducted aerial tests using a Jetstream as a 'surrogate' UAV. Meanwhile in the US, General Atomics and NASA conducted a trial in November using an Ikhana (NASA MQ-9) equipped with three sensors — ADS-B, TCAS and an air-to-air radar, with a view for further trials this summer.   

But Europe has not been sitting still either. At the end of April, the EDA announced that, together with the MIDCAS (Mid Air Collision Avoidance System) consortium, a UAV demonstrator had concluded a successful flight test and simulation campaign to trial D&A technologies.

Formed in 2009, the €50m MIDCAS is the European D&A project, and has as its members Airbus D&S, Sagem, Thales, Diehl BGT Defence, DLR, ESG, Indra, Alenia Aermacchi, Selex ES, CIRA with Saab as the overall team leader.


The trial flights saw a highly modified and upgraded  Alenia Sky-Y RPAS system fly since December 2014, racking up ten test flights over the course of the flight test campaign. Flying from Grazzanise Air Base in Italy, the Sky-Y performed fully automatic avoidance manouevres using both cooperative and non-cooperative sensors. Non-cooperative sensors are especially important as although most commercial airliners will now be equipped with ADS-B, it is GA and light aircraft that may not be squawking or in communication with ATC that present the biggest risk.

To 'detect' both co-operative and non-cooperative targets the Sky-Y RPAS was equipped with ADS-B and an IFF interrogator as cooperative sensors and Radar, EO and IR as non-cooperative sensors. Data from these is then fused to give a picture of potential conflicts. Field of View (FoV) for the non-cooperative sensors, says EDA, is a little below the +/-110 deg in azimuth and +/-15 deg in elevation.

Testing, testing 

As noted earlier, the test flights saw MIDCAS fly the Sky-Y demonstrator from Grazzanise air base, just north of Naples in a segregated test area. There the team first worked up to the unmanned flights by de-risking them using a CASA C212 as a 'surrogate' UAV with the D&A system fitted and a Falcon 20 as an intruder target.

For the real unmanned tests, the Sky-Y was flown with a C-27J tactical transport as a target. The speed of the UAV was typically around 95kt, with the intruder flying around 140kt. Closing speeds, say EDA, depended on the scenarios, with the highest being recorded in head-on conflicts of around 240kt. All tests were flown in daylight, under varying conditions.

Levels of autonomy

HUD from the operators point of view showing suggested evasive manouevre. (EDA)

Detecting an incoming threat, though, is only half the battle. The next stage of the process is 'avoid' and the MIDCAS trials saw the Sky-Y perform a dynamically calculated manoeuvre to maintain separation and avoid conflict. According to EDA, the avoiding action also included warnings to human operators on the ground, before the autonomous system took evasive action from the intruder. The autonomous decision making was spilt into three stages:

1) inform the RPAS pilot of surrounding traffic and any potential conflict

2) alert the RPAS pilot for the need for traffic avoidance, in which case the pilot can choose to activate an automatic traffic avoidance manoeuvre

3)alert the RPAS pilot of a pending collision risk in which case the pilot can choose to make an early activation of an automatic collision avoidance manoeuvre. If not activated by the pilot the system will automatically activate the collision avoidance manoeuvre when necessary.

The autonomous avoidance manoeuvres came in two flavours - a relatively 'benign' traffic avoidance  consisting of a left/right or climb/descent  — along with a more aggressive anti-collision manoeuvre that combined a turn with an up/down at the maximum performance of the UAV.



Derisking D&A is critical for the flexibility of operating larger, more complex UAVs/UCAVs. (Dassault)

With the flying tests and ground simulation activities complete — the MIDCAS team is currently involved in analysing the data and also making it exploitable for partners and interested parties. Says EDA: "One of the aims is to share some IPR (intellectual property rights) between partners and to drive the standardisation process, which is needed for exploitation of any technical results. That said, there is clearly a common interest in the area of standardisation and certification, and there is friendly dialogue facilitated by EDA, but this is bounded by the respective contractual arrangements and related IPR".

These trials then have been an important milestone in proving that larger UAVs can safely share the skies with manned aircraft - even one that all not equipped with IFF or ADS-B and that ATC may be essentially blind to.

Notes the EDA: “The MIDCAS concept of operations is informing the debate at EASA and ICAO, as there is no substitute for actually trying to build and fly things. We currently need to keep technology, standardisation and regulation all moving along together.” 

26 May 2015