Investigators have revealed a fourth incident involving a Boeing 787 deviation from the localiser path, during an ILS approach to runway 25R at Hong Kong last year.

The incident occurred to an Ethiopian Airlines 787-8 which had been arriving on 18 July.

It had been cleared for the ILS approach to 25R but, shortly after passing the RIVER waypoint, the aircraft “kept diverging” to around 1nm north of the approach path, says the Hong Kong Air Accident Investigation Authority.

The twinjet (ET-ASG) also descended to an altitude of 3,700ft, coming within 570m horizontally of terrain rising to 3,277ft.

Air traffic controllers transmitted a warning to the crew and instructed the flight to climb to 4,500ft, after which the aircraft positioned for another ILS approach and a safe landing.

While none of the 235 occupants was injured, the incident bears a remarkable similarity to three other events – all involving 787s – which took place over the following three months, all in the vicinity of the RIVER waypoint during approaches to 25R.

The RIVER waypoint is about 16nm from runway 25R and close to the Tai Mo Shan peak.

Two of the three subsequent incidents occurred to Virgin Atlantic 787-9s while the other involved an Etihad Airways 787-9.

Ethiopian’s service had been arriving from Manila, in darkness, at the time of its deviation. Weather conditions and visibility were good, according to meteorological data from Hong Kong airport.

All of the events are under investigation.