Singapore Airlines (SIA) flight SQ321 from Heathrow to Singapore lost 178 feet in altitude in 4.6 seconds as it flew over Myanmar last Tuesday (21 May), according to Singapore’s Transport Safety Investigation Bureau (TSIB). The aircraft, a Boeing 777, was diverted to Bangkok.

A 73-year-old British man, named as Geoffrey Kitchen from Thornbury, died of a suspected heart attack following the incident, while dozens more were hurt – some seriously. SIA on Wednesday (28 May) said 42 of the passengers who were onboard the flight remained in Bangkok, 26 of whom are continuing to receive medical treatment.

The TSIB’s preliminary findings lay out just how quickly the incident unfolded; its report states that after about 20 seconds of "slight" turbulence, the aircraft experienced "a rapid change" in gravitational force (G) over a 0.6-second period "likely resulting in the occupants not belted up to become airborne".

Over a further four-second period, the aircraft’s vertical acceleration changed from -1.5G to +1.5G, which the TSIB said was likely to have resulted in those not belted in to fall back down.

"The rapid changes in G over the 4.6-second duration resulted in an altitude drop of 178 feet, from 37,362 feet to 37,184 feet," said the TSIB. "This sequence of events likely caused the injuries to the crew and passengers.

The report states that during the period of light turbulence that proceeded the major dip in altitude, "it was heard that a pilot called out that the fasten seat belt sign had been switched on".

SIA chief executive Goh Choon Phung has apologised for the "traumatic experience" suffered by the 211 passengers and 18 crew onboard the aircraft, adding SIA’s "deepest condolences" went out to Mr Kitchen’s family.

SIA on Wednesday (29 May) said it was fully cooperating with the ongoing investigation. "We are committed to supporting our passengers and crew members who were onboard SQ321 on that day, as well as their families and loved ones," said the carrier in a statement. "This includes covering their medical and hospital expenses, as well as any additional assistance they may need.

"We deeply appreciate the invaluable assistance provided by the governments of Singapore and Thailand, as well as our many partners and the medical teams in both countries and around the world.

"We are also humbled by and grateful for the encouragement from our passengers and members of the public."