What happened
On March 24, 2018, at approximately 16:00 local time, a Cessna 172N with registration YR-FLY attempted to take off from runway 15 at Măgura-Cisnădie Aerodrome in Sibiu County, Romania. The aircraft was owned by S.C. Sky Tour Transilvania S.R.L. and operated privately. The flight involved two persons on board: a pilot with 109 hours of experience and a co-pilot/instructor with over 10,000 hours. Both individuals survived the incident without injury.
The crew had assessed the grassy runway as having a layer of snow that appeared frozen underneath. After consulting METAR data from nearby Sibiu Airport, which indicated temperatures around 3°C and broken cloud cover at 5,000 feet, the pilot aligned the aircraft for takeoff. Flaps were set to 10 degrees, and the roll commenced.
As the aircraft accelerated, the pilot noted unusual resistance in the rudder controls. Upon reaching rotation speed, the nose wheel lifted, but the aircraft failed to accelerate adequately. The pilot continued the takeoff attempt, believing there was sufficient remaining runway. However, as the aircraft passed a section of the runway with significant terrain variation and accumulated mud due to poor drainage, braking forces increased dramatically. The aircraft reached the end of the 600-meter runway at minimum speed.
Attempting to maintain level flight immediately after leaving the ground, the pilot inadvertently extended the flaps to 40 degrees instead of retracting or maintaining the initial setting. This sudden increase in drag caused a rapid loss of airspeed and altitude. The aircraft touched down approximately 60 meters beyond the runway threshold, bounced, and then struck the ground violently at three points before hitting a tree with its right wing. The impact severed the tree branch, causing the aircraft to yaw 220 degrees to the right before coming to rest 240 meters from the runway end. The aircraft was destroyed.
The investigation
The Romanian Civil Aviation Safety Investigation and Analysis Authority (AIAS) investigated the occurrence. Key elements examined included:
- Runway Conditions: Runway 15 is a 600-meter grass strip with no lighting system, approved for daytime VFR operations only. On the day of the accident, the runway was covered in wet snow and ice due to partial defrosting from positive temperatures and sun exposure. A lack of drainage systems led to muddy patches along the runway.
- Aircraft Configuration: The Cessna 172N was equipped with main landing gear fairings, which the investigation found contributed to mud accumulation on the wheels, increasing rolling resistance.
- Performance Calculations: Using the Pilot’s Operating Handbook and EU regulations for contaminated runways, the required takeoff distance was calculated at 1,085 feet (330 meters) for a gross weight of 2,067 lbs. While this distance was theoretically within the runway length, the actual performance was degraded by surface conditions not accounted for in standard dry-grass calculations.
- Crew Actions: The investigation noted that neither pilot rejected the takeoff despite realizing the aircraft was not accelerating properly past the midpoint of the runway. The co-pilot, who was also the instructor, did not intervene to call for a abort.
Findings
The primary cause of the accident was the failure to achieve adequate takeoff performance due to an erroneous assessment of the contaminated runway surface and the aerodynamic drag caused by mud accumulation on the main gear fairings. Contributing factors included:
- Inadequate Runway Assessment: The crew underestimated the impact of wet snow, ice, and mud on acceleration, particularly in the second half of the runway where drainage issues created deeper muddy areas.
- Poor Decision Making: The pilot continued the takeoff roll after recognizing insufficient acceleration, rather than rejecting it. The more experienced co-pilot failed to communicate or enforce a rejection decision.
- Configuration Error: After liftoff, the accidental extension of flaps to 40 degrees induced excessive drag at low speed, preventing recovery from the descent.
- Environmental Factors: Positive temperatures and solar radiation caused snow to melt into wet slush and mud, significantly increasing ground friction beyond standard contaminated runway factors.
Safety action
The AIAS issued a safety recommendation to the Romanian Civil Aeronautical Authority (RCAA) to emphasize the importance of accurate assessment of takeoff and landing runway surfaces during civil aviation safety meetings. This aims to improve pilot awareness regarding the specific risks of grass runways in winter conditions, particularly concerning drainage and surface contamination.