Soccer Football - Premier League - Leicester City v Burnley - King Power Stadium, Leicester, Britain - November 10, 2018 General view of tributes left outside Leicester City's King Power stadium, after the club's owner Thai businessman Vichai Srivaddhanaprabha and four other people died when the helicopter they were travelling in crashed as it left the ground after their last home match Action Images via Reuters/Craig Brough

LONDON (Reuters) - British air accident investigators looking into the cause of the helicopter crash that killed Leicester City soccer club owner Vichai Srivaddhanaprabha said on Wednesday they are focusing on a problem with the tail rotor system.

The helicopter’s manufacturer has issued a safety alert to all owners of the particular model AW169 involved in the crash, Britain’s Air Accidents Investigation Branch said.

The manufacturer had been told to carry out a “precautionary inspection” of the system which controls the tail rotor.

“Investigation of the tail rotor control system is being carried out as a priority,” the air accident investigators said in a three-page report.

Thai businessman Vichai, 60, was killed last month along with four others when the helicopter crashed outside the King Power Stadium in the central English city of Leicester after a Premier League match.

Vichai bought the unheralded central England side in 2010 and went on to stun the soccer world by beating odds of 5,000/1 to win the Premier League title in 2016.

Investigators have so far found that at the time of the crash the weather was good with clear visibility.

The aircraft reached an altitude of approximately 430 feet before plummeting to the ground, investigators said.

They said the helicopter hit the ground in an “upright position on a stepped concrete surface”.