A mother and her two daughters who died when their car skidded on oil and crashed into an oncoming vehicle might not have died if a leaking crane had been properly maintained.

A sheriff ruled that the spill on the A92 at Cyrus, Aberdeenshire, three years ago, appeared to have been caused by a mobile crane which had a hose wrongly installed.

Sheriff Kenneth Stewart said that the Citroen Saxo containing 45-year-old Ann Copeland and her daughters Niamh, aged 10, and seven-year-old Ciara, lost control and skidded into an oncoming Berlingo van because of "contamination" on the southbound carriageway.

The most likely culprit for the leak was a crane operated by William Whyte Cargo Handlers Ltd, which passed along the road shortly before the crash.

The oil leaked out from a hole in a hydraulic hose which had been positioned incorrectly, causing abrasion.

The sheriff said the fault would probably have been noticed if William Whyte Cargo Handlers had a programme of "planned preventative maintenance" in place based "at least" on the recommendations in the manufacturer's manual.

In a written determination, he wrote: "It is likely that proper maintenance of the crane would have resulted in that fault being observed and corrected by re-routing of the hose and as a result it is unlikely that the hose would have failed and caused leakage of hydraulic fluid at the locus, and that the deaths may thereby have been avoided."

Mrs Copeland was a keen athlete and a member of the local Fleet Feet Triathletes club, while the two girls attended St Margaret's Primary School in Montrose.

Several witnesses told the fatal accident inquiry that the A92 was "extremely slippery in places" around the crash site.

Colin McLachlan, who was driving the Berlingo, said: "not even a top rally driver could have done anything with that skid".

The inquiry, held at Stonehaven Sheriff Court over 20 days between March and November 2011, heard that Whyte's now have a "preventative maintenance scheme" in place.

Sheriff Stewart recommended that the UK government "as a matter of urgency" bring in legislation to remove mobile cranes' current exemption from undergoing a compulsory regular roadworthiness test.

He also said William Whyte's employees appeared to misunderstand the purpose of the six monthly lifting operations and lifting equipment regulations 1988 (LOLER) examination, regarding it as an MOT for a crane when in fact it is a test of the safety of a crane's lifting equipment.

No-one from William Whyte Cargo Handlers Limited was available for comment.