Relatives of ten servicemen killed when an RAF Hercules aircraft was shot down in Iraq have urged a coroner not to be deterred from conducting a "full, frank and probing" inquiry.

Wiltshire Coroner David Masters was today due to start hearing evidence in an inquest into the tragedy which claimed the life of pilot, Flight Lieutenant David Stead, 35, of Burley-in-Wharfedale.

Sarah Chapman, sister of Sgt Bob O'Connor, 38, who was killed in the crash, said as she arrived at the coroner's court in Trowbridge, Wiltshire, yesterday: "We have waited three years to get to this point. There is only one inquest and it is of paramount importance that it is done correctly, and for truth and transparency to be upheld."

She said the lack of ESF (explosive-suppressant foam) on the stricken aircraft was at the top of her list of concerns.

The foam, which has been fitted on US Air Force Hercules aircraft since the 1960s, prevents fuel tanks exploding if they are hit by enemy fire. Australian Air Force Hercules have had ESF retrospectively fitted.

The MoD's lawyer Jonathan Glasson yesterday told Mr Masters that all RAF Hercules currently flying "routinely" in Iraq and Afghanistan had been, as of December last year, fitted with ESF. He did not say how many aircraft had been fitted.

The RAF Hercules came down between Baghdad and Balad air base on January 30 2005 after enemy gunfire pierced a fuel tank, which exploded blowing off one of the wings. Nine RAF servicemen and a soldier were killed.

It was at the time the biggest single loss of life among British forces in the Iraq campaign.

"It is a travesty that people have got to lose their lives before action is taken," said Miss Chapman, of Cambridge.

The other eight victims of the Hercules crash based at RAF Lyneham in Wiltshire were: RAF 47 Squadron's Flt Lt Andrew Smith, 25, the co-pilot; Master Engineer Gary Nicholson, 42; Flt Sgt Mark Gibson, 34; Australian airman Flt Lt Paul Pardoel, 35, a navigator; and from Lyneham's Engineering Wing, Chief Technician Richard Brown, 40, an avionics specialist; and Corporal David Williams, 37, a survival equipment fitter.

Also on board was Sqn Ldr Patrick Marshall, 39, from Strike Command Headquarters, RAF High Wycombe.

Acting L/Cpl Steven Jones, 25, of Fareham, Hampshire, a Royal Signals soldier, was a passenger on the Hercules.

Families, apart from that of Flt Lt Pardoel, were refused legal aid until two weeks ago.

A spokesman for the Legal Services Commission, which administers legal aid in England and Wales, said the aid was being back-dated to cover the costs of legal work on the case since November 16 last year.

After legal submissions, Mr Masters ruled that an inquest jury was not required.