Some of us are old enough to recall a 737 that made a very successful forced landing on a dike many years ago, due to a dual flameout. I just watched a good documentary on it, as part of the Air Disasters series. I was surprised that it was possible to fly the plane back out again after replacing one of the engines.
The subsequent investigation discovered that the flameouts were caused by a combination of heavy rain and hail when the thrust was reduced for descent, and that this problem wasn't discovered during certification testing because all of the precipitation-resistance tests had been done at cruise thrust. When the thrust was reduced to something like 35%, that's when the problem was found to be reproducible. This resulted in design changes and fleet retrofits to prevent future problems in this scenario.
The documentary is episode 11 of season 3 (entitled Nowhere to Land), and can be viewed on the Smithsonian Channel web site, using one of various video subscriptions to unlock the episode.
https://www.smithsonianchannel.com/details/series/air-disasters/season-3
The subsequent investigation discovered that the flameouts were caused by a combination of heavy rain and hail when the thrust was reduced for descent, and that this problem wasn't discovered during certification testing because all of the precipitation-resistance tests had been done at cruise thrust. When the thrust was reduced to something like 35%, that's when the problem was found to be reproducible. This resulted in design changes and fleet retrofits to prevent future problems in this scenario.
The documentary is episode 11 of season 3 (entitled Nowhere to Land), and can be viewed on the Smithsonian Channel web site, using one of various video subscriptions to unlock the episode.
https://www.smithsonianchannel.com/details/series/air-disasters/season-3