Clear air turbulence

Clear air turbulence is high-altitude turbulence in cloudless air, invisible to weather radar. On May 21, 2024, the Boeing 777-300ER operating Singapore Airlines flight SQ321 out of London flew into severe turbulence over Myanmar. According to the preliminary report of the TSIB (Transport Safety Investigation Bureau), vertical acceleration went from +1.35 g to -1.5 g in 0.6 seconds and the aircraft lost 178 feet in under five seconds. Unbelted passengers hit the ceiling. A 73-year-old British man died, probably of a heart attack, dozens were injured, and the aircraft diverted to Bangkok. Clear air turbulence comes from wind shear around the jet streams, with no cloud and no return on the onboard radar: the crew finds it by flying into it. A University of Reading study found that at a typical North Atlantic point, severe turbulence rose 55% between 1979 and 2020. For the insurer, the hull is almost never touched. The claim falls in passenger liability and is settled under the Montreal Convention on an international flight. Since Air France v. Saks in 1985, an Article 17 accident is an unexpected or unusual event external to the passenger; severe turbulence qualifies, ordinary cruise bumps generally do not. The carrier is strictly liable up to the first tier, 128,821 SDR (special drawing rights) at the time of SQ321, raised to 151,880 SDR on December 28, 2024. Above it, the carrier must prove it was not negligent, and the argument turns on the seatbelt sign and the weather information available. Crew injuries go through workers' compensation.