Air carrier flight crew reported severe turbulence in cruise flight.
Synopsis
Air carrier flight crew reported severe turbulence in cruise flight.
Narrative
Flying at FL350; we were cleared to deviate 55 nm west of course to circumvent a solid line of thunderstorms that was in excess of 100 nm wide; centered along our route of flight. We were cleared direct BWG; which was just under the west edge of the thunderstorm line; and deviated further west as we went around the west end of the storm. As we proceeded northwest to give additional clearance to the storm; MEM Center asked how much further north we needed to go and we told him we could turn northeast now as the weather radar was clear. He cleared to turn northeast direct HAGAL and made no mention of any weather along the route. We were in high clouds; so visibility was nil and EFVS (Enhanced Flight Vision System) was ineffective. Radar was showing absolutely no weather. Suddenly; we hit a wall of water that could have contained hail as far as we knew based on the sound (post-flight inspection found no damage) and severe turbulence which resulted in an immediate semi-controllable left bank (approximately 20 degrees) and an inability to accurately read the instruments. The PF (Pilot Flying) reduced the thrust manually and left the autopilot engaged. The turbulence was so severe; I got thrown to the right side over the armrest and the CA (Captain) was bounced up in his seat and hit his head on the HUD (Heads Up Display) projector housing (no injury). The hand mic; which was laying across my lap; was thrown off to the side. After about 30 seconds; the turbulence abruptly ended as we broke out into CAVU VFR conditions. NO LAND 3 was now displayed on the ASA (subsequently cleared itself after an ATC directed go-around at IND). Looking at Flightaware this morning; I see that an isolated thunderstorm is shown on our route of flight. I am not aware when that weather snapshot was taken; but it correlates with where we experienced the turbulence.At no point did we see any weather (not even light rain) on weather radar (we both had weather radar displayed); at no time did MEM Center advise us of the storm; and as soon as we exited; when I advised ATC of the severe turbulence and to have other aircraft avoid the area; he made no mention of seeing the weather on his system. We were running the weather radar tilt between 0 and +2 degrees. After we exited the weather; while troubleshooting why we may not have seen the weather; I noticed that the tilt was showing -2 when I expected it to show -10 (I tilted the radar down til the ground return equaled our AGL altitude). It is likely the tilt error was off that significantly due to the turbulence and probably didn't exist prior; but I have no way to know. Unobserved severe thunderstorm along the route of flight.Recommend continued installation of new weather radar in fleet.
Second reporter narrative
We had previously been deviating for weather east of BWG. We deviated west to hit BWG then we're told to proceed towards HAGAL on the GIIBS3 arrival to IND. We were heading towards HAGAL and we're asked if we were clear of weather and could take a turn towards GLNCH. We both confirmed the radar was clear and I did not see anything in EFVS (Enhanced Flight Vision System). Approximately 1 minute after turning towards GLNCH we dropped suddenly; heard very heavy rain; the plane banked left nearly 30 degrees and was shaking violently. My head just barely touched the HUD combiner during the initial drop. I pulled the power back to control the speed and monitored the autopilot to make sure it did not disengage. The ASA (Autoland Status Annunciator) then showed NO LAND 3 and would not reset. The entire event lasted roughly 30 seconds. We landed uneventfully and made a severe turbulence write up. Clear air turbulence
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.