What happened
On December 8, 2017, a Cessna 525B Citation CJ3, registration LX-WEB, was performing a non-commercial flight from Farnborough, England, to Annecy Meythet, France. During the approach, the crew encountered snow showers and wet runway conditions. After an initial missed approach due to poor visibility, the crew decided to attempt a second approach, believing the available runway length was sufficient for the contaminated surface.
Upon landing on runway 04, the crew found that braking effectiveness was extremely poor. As the aircraft approached the end of the runway and passed taxiway C, the pilot in command determined that the aircraft could not stop within the remaining distance. To avoid a longitudinal overshoot into obstacles at the runway end, the pilot intentionally steered the aircraft laterally off the runway to the left. The aircraft came to a stop in the dirt approximately 150 meters before the runway end. The aircraft sustained minor damage to its flaps, and the main tires showed signs of abrasion from the use of the emergency brake.
The investigation
The BEA investigation focused on the crew's performance calculations and the software used during flight preparation. The investigation examined the use of the "Guru" application on the crew's Electronic Flight Bag (EFB). It was found that because the operator had not provided specific wet runway data to the software developer, the application applied a 15% margin to dry runway distances. This method resulted in an underestimation of required landing distances for wet runways.
Furthermore, the investigators analyzed the crew's manual application of the Aircraft Flight Manual (AFM) tables. The crew attempted to calculate distances for contaminated runways by using the incorrectly calculated wet runway distance as an input, rather than using the dry runway distance as required by the AFM instructions. This secondary error further reduced the calculated landing distances.
Findings
- The crew's landing performance calculations were fundamentally flawed due to incorrectly using the wet runway distance as the base value when applying AFM contamination tables.
- The EFB software used by the crew underestimated required landing distances on wet runways because it relied on an arbitrary 15% margin rather than the specific values found in the AFM.
- The crew did not recalculate their performance requirements during the second approach, relying instead on the erroneous pre-flight calculations.
- The pilot's decision to intentionally steer the aircraft off the runway prevented a more serious longitudinal excursion into the obstacles located at the end of the runway.