Schweizer Sturmforum

Turbulence is a definite candidate as a contributing factor. There is an isolated storm at (1.6,-31.5) that appears suddenly at 0200Z just as the A330 enters the main MCS cluster. From a turbulence perspective it is by far the most dangerous formation found on the loop. However it is 10-25 km to the left of UN873 and it is doubtful the crew would have been deviating at this time. Other cells like this one embedded within the main MCS may have caused severe turbulence. Young updrafts are particularly dangerous to flights because they contain significant rising motion yet precipitation fields have not yet fully developed and airborne radar signatures are weak, reducing the likelihood the crew will deviate around the cell. Another concern is the extensive upper-level dry air shown on the SBFN sounding (not counting the anvil debris at 350-300 mb), which may have contributed to enhanced evaporative cooling in and around the anvil and aggravated the turbulence experienced by the flight, especially around the margins of anvil clouds and towers. It is worth considering that cumulative periods of heavy turbulence crossing through the cluster may have caused minor internal damage that progressed in some way into an emergency.