You don't say?

Well, they got something right.

Commercial airliners are designed to glide at altitude under engine failure. At cruising altitudes over 30,000 ft your looking at somewhere around 20-30 minutes of glide time for most large jet aircraft. My guess is that these particular planes may have some feature or defect which this agency is reporting on which makes it difficult for a pilot to keep the craft in the flight envelope under glide, or reduces glide performance.