What happened
On December 17, 2017, at approximately 23:45 CST, SkyWest flight 5788, an Embraer ERJ170-200LR (registration N128SY), was performing a scheduled domestic flight from San Francisco International Airport (SFO) to St. Louis International Airport (STL). The flight was operating under 14 CFR Part 121. During the descent, the flight crew realized they had passed the top of descent point for their programmed 3-degree descent path.
To manage the descent, the captain instructed the first officer to select a flight level change. This maneuver caused the descent rate to briefly exceed 5,000 feet per minute and led to an increase in airspeed. Although the first officer deployed the speed brakes per the captain's instruction, the airspeed continued to rise. To avoid an overspeed condition, the captain disconnected the autopilot and performed a manual nose-up pitch correction.
During this sudden movement, a flight attendant preparing the galley was thrown to the floor. The flight attendant sustained one serious injury, specifically an ankle fracture, and was treated at a hospital following the landing. There were no fatalities and the aircraft sustained no damage.
The investigation
The crew reported that the air was smooth with no turbulence at the time of the event. The first officer was on his second day of initial operating experience (IOE) and was acting as the pilot flying, while the captain acted as the pilot monitoring. Air traffic control had previously cleared the aircraft direct to STL and requested the crew maintain their best forward speed.