Date: 201710
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: Turbulence; 50
Light: Daylight
Aircraft: DA40 Diamond Star
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Seatbelt
Component problem: Failed
Reporter organization: Personal
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Commercial; Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Instrument
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; General Physical Injury / Incapacitation; General Maintenance Action
Contributing factors: Aircraft; Weather
Primary problem: Aircraft

Narrative: After passing northeast bound through a mountain pass; I warned my passengers to expect turbulence. We started to experience moderate turbulence and then encountered a sudden violent drop in altitude. All four of us hit our heads on the roof of the airplane. No serious injuries; but possible head and spinal issues noted the next day. Two headsets were broken. The seatbelts did not prevent head strikes and two seat belts became unfastened. The front right possibly was not securely 'clicked' in place and the right rear came out of floor mount (looks like it was 'clicked' into an inaccessible latch under back seat) and could not be reattached during or after the flight without maintenance assistance.Reported the incident as 'severe turbulence' to Center; telling them we had struck our heads on roof of airplane. They were concerned and asked if we needed assistance. Each controller that followed checked in on how we were doing.The Diamond seat belts are particularly difficult to fasten securely. They are hard for larger persons to reach and securely latch and they did not appear to be effective at preventing head strike. Maybe the lap belts should have been tighter? Wind on the windward side of the pass at this altitude was about 25-30 knots. I did not notice the wind speed at the time of the incident on lee side of pass; but noticed it was over 40 knots (tailwind) as we continued northeast bound toward our destination. We modified course to get farther away from the mountains for the remainder of the flight.

Callback: The reporter stated the seat belt that the passenger in the right seat was using may not have been completely fastened because of the difficulty of accessing the buckle. The reporter stated that in order to ensure that the front seat belts are properly fastened you need to open the door to gain access to the buckle (especially if you're overweight). The reporter also stated one of the seat belts for the passengers in the rear seat became unlatched from the mount (which rendered it ineffective) and had to be reattached by Maintenance. Reattaching the seat belt required removing the rear seat. The reporter also stated that due to the low ceiling; the seat belts; as designed; will not prevent you from contacting the ceiling with your head during turbulence. The reporter stated that he broke his headset as a result of hitting his head on the ceiling.



Synopsis: Diamond DA40 pilot reported encountering severe turbulence while traversing a mountain pass. He and all the passengers hit their heads on the ceiling when the seatbelts became ineffective.