The father of two women killed in a helicopter crash said he hoped the case would serve as a lesson to pilots after an inquest recorded an open verdict.
Four people died in the 1998 crash near Market Harborough
Andrew Byrne, 36, wife Helen Linhart, 31, and her sister Katie, 26, were flying in bad weather conditions at night, near Gumley, Leics, in 1998.
They were killed instantly, along with their pilot James Coulter.
He had been warned about his "casual attitude" to flying by the Civil Aviation Authority months earlier.
Mr Coulter had taken the trio on a pleasure trip. An inquest after the April 1998 crash recorded verdicts of accidental death for the four victims, but three of the verdicts were later overturned in the High Court.
An inquest jury at Leicester Town Hall returned open verdicts on Thursday into the deaths of the three passengers after coroner Martin Gotheridge told them the evidence did not reveal the cause of the crash.
He said: "We do not have evidence that actually tells us what caused the crash nor do we know for certain who was operating the controls in the helicopter immediately before the impact.
"The only conclusion that I believe you can safely come to here is an open verdict."
'Night Flying dangers'
He said there was not enough evidence for either unlawful killing or accidental death verdicts.
Michael Linhart, 79, and his wife Mary, who have been left to look after their daughter's three children, said the case had highlighted the dangers of night flying.
Mr Linhart, who is battling prostate cancer, said: "It sends a warning to the pilots of helicopters and the public alike of the dangers of night flying.
"If we have saved just one life we have the knowledge that our daughters and son-in-law did not die in vain and this will serve as an everlasting monument to their memory.
"At least their deaths are not seen as an accident any more. It was not an accident. My two daughters and son-in-law died and they should not have."