British air accident investigators looking into the cause of the helicopter crash in which Leicester City owner Vichai Srivaddhanaprabha died 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 on Wednesday.
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, died last month along with four others when the helicopter crashed outside the King Power Stadium following Leicester's home draw with West Ham.
Vichai bought the club in 2010 and went on to stun the football world by beating odds of 5,000/1 to win the Premier League title in 2015-16.
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 falling to the ground, investigators said.
They said the helicopter hit the ground in an "upright position on a stepped concrete surface."