American Airlines flight 748 experienced turbulence enroute to Comunidad De Madi (MAD), Madrid, Spain. As a result of the turbulence, three flight attendants sustained injuries, two being serious, while one passenger sustained a minor injury. The airplane was not damaged, and the flight crew continued to MAD where they were met by emergency medical technicians (EMTs) upon landing. The flight was a regularly scheduled passenger flight from Charlotte International Airport (CLT), Charlotte, North Carolina to MAD. The flight crew reported having a view of lightning at about an 11 o’clock position. The onboard radar also indicated rain ahead of them. Upon confirming that the sky above them was clear of any cloud cover or weather, the flight crew requested an up to 20-mile deviation of course to avoid the weather ahead, to which air traffic control (ATC) approved. As they approached the area where the radar had previously shown that there was rain, the radar was no longer showing rain and the flight crew could see no signs of rain directly ahead of them. The flight crew reported attempts to reference both of their personal weather apps to confirm the weather shown on the cockpit radar but was unsuccessful due to the lack of internet connection. Because of this, the flight crew concluded the weather to have passed and subsequently decided to no longer deviate from the original course. The unexpected turbulence event was experienced soon after. The flight crew reported that the turbulence was sudden and came without warning. The cabin crew reported they were preparing for arrival service into MAD when they experienced a “sudden loss in altitude” and a series of jolts. The flight and cabin crew both reported that the turbulence lasted around 30 - 40 seconds and that flight crew reported that the autopilot disengaged but did not cause a deviation in altitude of more than 200 feet. Three flight attendants reported they were preparing the back galley for meal service when the unexpected turbulence occurred, causing all three flight attendants to be thrown in the air and “slammed” on the floor. The flight attendants also reported that a passenger was thrown in the air and hit their head. After landing, the three flight attendants were seen by EMTs, and all were taken to the local hospital for further care. The flight crew was aware of thunderstorms in the area, subsequently the seatbelt sign was on, but no announcement was made to inform passengers or cabin crew of potential turbulence. The flight crew informed ATC about the injuries and requested EMTs to meet the airplane upon arrival.