These are the commercial jet engines you see, like the Boeing 777, 747, Airbus A330 and A380s. Though there is a considerable reduction of the engine thrust, at these altitudes the lower drag associated with low air density means a more economical flight with a higher True Air Speed.
Crepitus in the knees may be caused by knee injuries such as meniscus tears. These are fairly common in people who play sports, jog, or run. A meniscus tear can cause crepitus as the joint moves. Chondromalacia patella is a dull ache behind the kneecap, usually caused by overuse or injury. There will be damage to the undersurface cartilage covering the kneecap.
What Causes Joint Crepitus? Common causes of creptius include: Air bubbles popping inside the joint. This popping does not cause pain. Tendons or ligaments snapping over the joint's bony structures. This snapping sometimes causes pain. Arthritisâtypically either osteoarthritis or rheumatoid arthritisâthat causes a jointâs articular cartilage to degenerate. While arthritis often leads to pain, not everyone with joint degeneration will experience it.