What happened
On June 2, 2003, a Cessna Citation II, registered N18HJ, was performing a commercial flight from Falköping, Sweden, to Amsterdam Schiphol. While traversing German airspace, the flight crew began their descent and interacted with Dutch air traffic control. Due to deteriorating weather conditions, the controller suggested a course deviation to either the left or right to avoid cloud cover. The crew elected to deviate to the left, choosing a heading of 180 degrees to maintain better visibility.
While flying at 15,000 feet, the aircraft encountered severe turbulence and the heavy impact of hail. The pilot flying responded by reducing airspeed, activating the anti-ice systems, and disconnecting the autopilot. Passengers were instructed to secure their seatbelts during the three-minute period of intense weather. Although the crew completed the landing at Schiphol without further incident, they only discovered the extent of the damage once the aircraft had stopped on the ground. The impact resulted in substantial damage, including the total destruction of the fiberglass radome and deep denting to the aluminum skin of the wings and fuselage.
The investigation
The investigation, conducted by the Dutch Safety Board in coordination with German authorities, utilized radar data to confirm the aircraft had entered German airspace during the event. Analysis of radar tapes revealed that the N18HJ had flown directly through the center of a cumulonimbus cloud. Investigators also reviewed the crew's flight preparations, noting that while they were aware of forecasted thunderstorms, they had no reason to cancel the flight.
Findings
- The primary cause of the incident was the unexpected penetration of a cumulonimbus cloud.
- The crew's decision to deviate left was intended to avoid weather, but the deviation was insufficient to bypass the squall area.
- The weather radar was not activated prior to the encounter, which prevented the crew from identifying the core of the storm in time to avoid it.
- The crew noted that the radar system required approximately three to four minutes to become operational, making it too late to use once the aircraft entered the clouds.