Collision tests to assess the potential damage which a drone could inflict on aircraft indicate that airliner windshields are relatively resistant to a strike.

Testing intended to determine the lowest speeds at which critical damage could occur found that cockpit penetration was possible, albeit with a heavier drone, some 4kg, at high closing speeds.

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Farnborough-based technology firm Qinetiq and collision specialist Natural Impacts carried out the research on behalf of the UK Department for Transport, the Military Aviation Authority and pilots' union BALPA.

While the final analysis of the experiments does not give specific details, FlightGlobal understands that the windshield penetration occurred at a substantially higher speed than the 250kt to which aircraft are typically restricted below 10,000ft. The European Aviation Safety Agency, in a similar collision study last October, assumed aircraft would be travelling at a calibrated airspeed of 340kt above 10,000ft.

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Qinetiq's analysis concluded that airliner windshields "could retain integrity" during impacts with drones at typical later-stage approach and landing speeds, even after sustaining substantial damage.

The airliner testing primarily used a cockpit windshield constructed of three glass layers, and the live tests were complemented with the use of computer modelling.

Modelling and testing, says the analysis, showed that severe windshield damage "did not occur" at higher altitudes and speeds with drones in the 1.2kg category.

But it adds that such damage, including structural failure, "could occur" under these conditions with a 4kg drone.

One live high-speed test, using a 3.5kg fixed-wing drone against a simpler windshield comprising only two glass layers, resulted in penetration. The analysis says the construction of a drone, including the exposure of metal parts, is crucial to the severity of an impact.

But the analysis also points out that the probability of encountering a heavy drone at high speeds – the combination which can cause critical damage – is "significantly less" than the risk of a collision with a toy device.

BALPA claims the testing, despite demonstrating the resilience of aircraft windshields, are a "robust verification" of its concerns over the drone collision threat.

The UK government, as it released the analysis, disclosed that it planned to introduce mandatory registration for drones over 250g and revealed plans for a safety-awareness test for owners.

BALPA is citing additional results of Qinetiq's testing which assessed the effects of drone impact on smaller aircraft types and, in particular, helicopters.

Helicopter tail rotors, and windshields which are not birdstrike-certified, are particularly vulnerable, even below normal cruise speeds, the analysis found. The windshield issue could also apply to general aviation aircraft.

Windshields which are birdstrike-certified "could still be critically damaged" at normal cruise speeds, it adds.

While the analysis has increased knowledge regarding the severity of an impact, it says, a full examination of the risks involved would require additional work in order to estimate the probability of a collision.