Sand is being blamed as the primary reason for a series of windscreen fractures that grounded several aircraft at Denver International airport on 16 February (Flight International, 27 February-5 March).

On that day 14 aircraft - owned by Frontier Airlines, SkyWest Airlines and Great Lakes Aviation - were grounded after 23 separate windscreens were hit by debris. US National Transportation Safety Board lead investigator Jennifer Kaiser says investigators have confirmed that all 23 windscreens had been peppered with "foreign object material" before the windscreens cracked. Kaiser says "sand was the glue" that tied all incidents together.

The NTSB will review these findings when Kaiser submits the report, which is currently being finalised in consultation with windscreen manufacturers PPG and Saint-Gobain.

The safety board opened its investigation after a Frontier Airbus A319 experienced a window fracture on climb-out from Denver on a flight to San Francisco. According to the preliminary report, the first officer's front windscreen was "cracking and beginning to burn and spark".

After reporting the situation to controllers and reversing course back to the airport, the captain's side window also fractured. The aircraft landed safely at Denver and there were no injuries.

The NTSB says wind velocities at the time were between 28kt (50km/h) and 36kt, with gusts as high as 44kt, as a cold front passed through the area. All fractures occurred within a 3h period.

Denver airport says it uses US FAA-approved sand "sparingly" and only at gate areas and perimeter entrances, not on taxiways and runways.

Source: Flight International