Singapore Airlines is offering initial compensation of $25,000 to some of the passengers on a flight from London last month that suffered severe turbulence, leading to one death and multiple severe injuries.

Those with injuries requiring long-term medical care have been offered an advance payment of $25,000. For those who suffered minor injuries in the May 21 incident, the airline has offered $10,000. The carrier said in a social media post on Tuesday that it had sent the offers to passengers on June 10.

A law firm representing some of the passengers said it was advising everyone to seek legal advice before signing anything with Singapore Airlines.

“Our working theory remains that this incident could have been avoided and therefore some fault lies with Singapore Airlines,” said Peter Carter, director of Carter Capner Law. “Our team, which includes very experienced airline captains, believes there is evidence to suggest that the aircraft flew through the top of a thunderstorm or in proximity to one as it passed over an area notorious for thunderstorm activity in the Inter Tropical Convergence Zone.”

Singapore Airlines responded: “We regret that we are unable to comment on the views of other lawyers. SIA is fully co-operating with the relevant authorities in the investigation into this incident.”

Earlier, the airline said it had invited those who sustained more serious injuries “to discuss a compensation offer to meet each of their specific circumstances when they feel well and ready to do so.”

“Passengers medically assessed as having sustained serious injuries, requiring long-term medical care, and requesting financial assistance are offered an advance payment of $25,000 to address their immediate needs. This will be part of the final compensation that these passengers will receive.”

The airline confirmed it had also given passengers S$1,000 (US$740) for immediate expenses following the flight. It said it would provide a full refund of airfares to all passengers, including those who did not suffer any injuries.

One person died and dozens were hurt, including suffering severe spinal and brain injuries, when Flight SQ321 from London to Singapore experienced sudden, extreme turbulence over the Irrawaddy basin in Myanmar. The flight was diverted to Bangkok.

The aircraft dropped 178ft in under five seconds, with passengers experiencing rapid changes in g-force, or vertical acceleration, according to a preliminary chronology of events compiled by Singapore’s Transport Safety Investigation Bureau, the US National Transportation Safety Board, the Federal Aviation Administration, and Boeing.

The flight underwent an “uncommanded” increase in altitude and airspeed while the autopilot was switched on, which the report said was most likely due to the aircraft being hit by a rapid upward movement of air, which lifted it more than 360ft.

Overall the incident lasted just over a minute before the flight returned to its planned altitude.

The preliminary report, based on data from the aircraft’s “black box” flight recorder, said it was probably flying over an area of developing convective activity at 37,000ft when the turbulence hit. Convective weather usually refers to thunderstorms or developing clouds. A probe by the Transport Safety Investigation Bureau is ongoing.

News of the Singapore Airlines payouts came after an Austrian Airlines aircraft on Sunday suffered such severe damage from a hailstorm that its nose cone was torn off and the cockpit windows were severely damaged.

The aircraft, flying from Palma de Mallorca, encountered the storm shortly before arriving at Vienna’s Schwechat Airport. The airline, part of Germany’s Lufthansa Group, said in a statement that the aircraft, including the cockpit windows, aircraft nose, and coverings, had been “damaged by hail.”

“The aircraft encountered a thunderstorm cell during approach to Vienna, which according to the cockpit crew, was not visible on the weather radar,” the airline said. The airline said all passengers on the flight were unharmed.

The crew of the flight — carrying 173 passengers and six crew — issued a Mayday call because of the extent of the damage, the airline said, adding that the flight had landed safely in Vienna.