Relatives of victims of the Shoreham airshow disaster in which 11 men died have expressed their disappointment after the display pilot who crashed a vintage Hawker Hunter jet was cleared of manslaughter.

Andrew Hill, 54, a former British Airways captain who was also an RAF flying instructor, was accused during his trial of flying “too low and too slow” as he attempted a “bent loop” manoeuvre. He claimed he experienced “cognitive impairment” while at the controls, brought on by hypoxia possibly due to G-force.

Up to 20,000 spectators were at the airshow when the 1950s ex-military jet crashed on to the A27 in West Sussex and erupted into a fireball on 22 August 2015.

Facebook Twitter Pinterest The vintage jet just before the Shoreham airshow crash in 2015. Photograph: Sussex police/CPS/PA

The 11 who died were Maurice Abrahams, 76; Dylan Archer, 42; Tony Brightwell, 53; Matthew Grimstone, 23; Matt Jones, 24; Graham Mallinson, 72; Daniele Polito, 23; Mark Reeves, 53; Jacob Schilt, 23; Richard Smith, 26; and Mark Trussler, 54. They all lived in Sussex.

Hill was seriously injured after his cockpit separated from the rest of the aircraft and his seat was thrown clear. He was found partially conscious near burning wreckage.

He told jurors he had no memory of the crash or the events immediately before it and had never watched video footage of it, and he said the devastation caused was a dominant thought in his everyday life. He denied 11 counts of manslaughter by gross negligence.

Shoreham airshow disaster: the 11 victims Read more

Speaking outside the Old Bailey in London following his acquittal, Hill read out the names of the 11 men and said: “I’m truly sorry for the part I played in their deaths.”

Families of those killed wept as the unanimous verdicts were delivered after seven hours of deliberations. The judge, the Hon Mr Justice Edis, acknowledged that the relatives were “enormously upset” and he praised the “very dignified way” they had conducted themselves during the two-month trial.

Matthew Grimstone’s parents, Sue and Phil Grimstone, said the outcome set an alarming precedent for airshows, and they questioned whether displays should be allowed if there was risk of cognitive impairment.

Leslye Polito, the mother of Daniele, a builder, said she was extremely disappointed and felt let down by the justice system. She is one of many who have called for the Shoreham airshow not to take place again as a mark of respect.

The families have called for a “thorough and frank” investigation to prevent future tragedies and will now look to the inquest into the deaths to provide answers.

The prosecution claimed Hill was flying at 2,800ft and failed to select full throttle as he began the ill-fated bent loop. A safe height would have been about 4,300ft, the court was told. He also failed to perform an escape manoeuvre, it was claimed.

Hill, an A-grade student and Cambridge University graduate, was regarded as a respected and competent pilot, the court heard. He joined the RAF after Cambridge, and as a top-performing pilot he was selected as an instructor. He later joined Virgin Atlantic and then moved to British Airways, reaching the senior position of captain.

He was said to have told paramedics after the crash that he had blacked out at the controls. Subsequent medical checks could not establish any condition that might have affected his health, jurors heard.

In hospital he was placed in an induced coma having sustained fractures to his nose, ribs and part of his lower spine, as well as a collapsed lung and serious bruising. He was discharged after a month.

Accounts from survivors read to the courtroom described how they were blown off their feet and then ran for their lives to escape the fireball. Some sustained terrible burns. Of those who died, five were in vehicles. The others were either watching the airshow from a roadside grass verge or waiting to cross the road.

All Hawker Hunter jets were grounded immediately and regulations have since been tightened to limit some displays to flypasts. Shoreham was the greatest loss of life at an airshow since 31 people including the pilot died at Farnborough in 1952.

For a conviction for manslaughter by gross negligence, the jury had to be satisfied that Hill’s conduct was so bad as to amount to a criminal act or omission. Jurors were told that the case hinged on the question of whether the defendant was incapacitated in such as way that he was not in control of the aircraft.

One juror was discharged on the first day of the trial after telling court staff he could never convict anyone over the crash because it was an accident, it can now be reported.

DI Jon Fanner, of Sussex police, said it had been a “long, complex and unique investigation”. While he respected the verdict, it had been “clearly appropriate” for Hill to stand trial, he said.

Sarah Stewart, a partner at the law firm Stewarts, representing some of the relatives, said compensation claims had been settled. She added: “Many families do not look for compensation. They want answers so that future deaths can be prevented.”

She said the families had had to “painfully relive the circumstances of their loved one’s death again and again”. The verdicts went some way towards providing answers, “but it is only one part of the jigsaw”, she said.

Rebecca Smith, of the law firm Irwin Mitchell, representing others affected, said: “While there have been some recommendations from the Air Accident Investigation Branch following their early reports, it is only once the whole event has been examined at the inquest that lessons can be fully learned to prevent something like this from ever happening again.”

Andrew Hill profile

Hill, a trained Royal Airforce instructor who was a British Airways captain at the time of the accident, grew up in Kent where he attended a private boarding school. After graduating in computer science he went straight into the RAF, winning a competition when flying a Jet Provost, and he was ranked a top-performing student and selected to become an instructor.

Training in combat, he took part in active service for a month in the 1990s, monitoring a no-fly zone in northern Iraq. He flew Harrier jets, capable of vertical take-off and landing, and won an award for ideas on improving aircraft safety procedures.

He became a commercial pilot with Virgin Atlantic before moving to British Airways and becoming a captain.

• This article was amended on 9 March 2019 to clarify in the second paragraph that Hill no longer works as a British Airways captain.