Paris-Le Bourget

Before starting the descent to destination, the crew listened to the Le Bourget airport ATIS which indicated the presence of severe icing between 3,000 and 5,000 ft. They carried out the approach applying the manufacturer’s normal procedure for an approach in non-icing conditions, the approach speed selected by the crew (Vref 97 kt) was thus 22 kt below the approach speed in icing conditions and was, according to the manufacturer, close to the stall speed in the event of ice contamination. At 3,000 ft, the crew activated the wing and stabilizer de-ice system for a period of 21 s which corresponded to a complete de-ice cycle. The crew indicated that they observed through the cockpit window that the ice which had built up on wing leading edges had broken up. They then deactivated the de-ice system and did not active it again. This decision was solely based on the visual observation of the wing leading edges. The presence of ice on the wing and stabilizer leading edges observed after the accident shows that ice built up on the aeroplane on final. The following hypotheses can thus be made:
• Either the light and clouds did not allow the crew to determine the actual degree of contamination of the wings.
• Or the shapes and thickness of this built-up ice were visible from the cockpit and in this case:
o after deactivating the de-ice system, the crew no longer actively monitored the leading edges to ensure that there was no formation of ice or,
o the crew observed this build-up of ice but underestimated the consequences of this.
In the conditions of the day, the aeroplane’s weight and the configuration selected by the crew, compliance with the manufacturer’s procedure for an approach in icing conditions would have meant that the aeroplane would not be able to land at Le Bourget airport. This was because firstly, in the event of a go-around with one engine inoperative, the aeroplane’s climb rate was not sufficient to safely clear obstacles. Secondly, the landing distance available was less than the landing distance required by the aeroplane. The crew told the BEA that they were aware of these limitations even before taking off and that they knew that if they had to continuously activate the de-ice system until landing, they would have to divert. Given that it was impossible to meet the operational constraints by strictly complying with the procedure, the strategy chosen by the crew was to carry out the landing according to the manufacturer's procedures for an approach and landing in non-icing conditions while ensuring that ice had not built up on the aeroplane. The captain explained that this was a standard adaptation of the procedure.
The deactivation of the de-ice system had the following consequences:
• The ice that may have built up on the leading edge of the horizontal stabilizer may not have been completely broken up.
• Ice built up again on the aeroplane at the end of the approach.
• The Stall Warning Protection System (SWPS) was not configured to cut in effectively in the icing conditions of the accident: the speed tape displayed on the PFD was not configured to alert the crew that they were flying at a speed close to the stall speed and the aural stall warning and the Stick Pusher protection were not configured to activate at the appropriate angles of attack.
Just before the impact, the aeroplane was flying in low speed and high angle-of-attack envelopes where the aircraft was likely to stall in case of ice contamination of its structure. The recorded flight data did not enable the exact degree of contamination to be determined, but the presence of ice on the leading edges of the wings and horizontal stabilizer observed after the accident confirmed that ice had built up on the aeroplane.

The accident occurred at nighttime under foggy conditions while it was taking off after cleared by the controller due to collision with the snowplow that executed runway incursion and stopped on the runway. Most probably, the accident was caused by the combination of the following contributing factors:
- lack of guidance on loss of control over an airdrome vehicle and/or situational awareness on the airfield in pertinent documents defining the duties of airdrome service personnel (airdrome shift supervisor and vehicle drivers);
- insufficient efficiency of risk mitigation measures to prevent runway incursions in terms of airdrome peculiarilies that is two intersecling runways;
- lack of proper supervision from the airdrome service shift supervisor, alcohol detected in his organism, over the airfield operations: no report to the ATM or request to the snowplow driver as he lost visual contact with the snowplow;
- violation by the airdrome service shift supervisor of the procedure for airdrome vehicles operations, their entering the runway (RWY 2) out of operation (closed for takeoff and landing operations) without requesting and receiving clearance from the ground controller;
- violations by the medical personnel of Vnukovo AP of vehicle driver medical check requirements by performing formally (only exterior assessment) the mandatory medical check of drivers after the duty, which significantly increased the risk of drivers consuning alcohol during the duty. The measures and controls applied at Vnukovo Airport to mitigate the risk of airdrome drivers doing their duties under the influence of alcohol were not effective enough;
- no possibility for the snowplow drivers engaged in airfield operations (due to lack of pertinent equipment on the airdrome vehicles) to continuously listen to the radio exchange at the Departure Control frequency, which does not comply with the Interaction Procedure of the Airdrome Service with Vnukovo ATC Center.
- loss of situational awareness by the snowplow driver, alcohol detected in his organism, while perfonning airfield operations that led to runway incursion and stop on the runway in use.
His failure to contact the airdrome service shift supervisor or ATC controllers after situational awareness was lost;
- ineffective procedures that resulted in insufficiently trained personnel using the airfield surveillance and control subsystem A3000 of A-SMGCS at the Vnukovo ATC Center, for air traffic management;
- no recommendation in the SOP of ATM personnel of Vnukovo ATC Center on how to set up the airfield surveillance and control subsystem A3000, including activation and deactivation of the Reserved Lines and alerts (as a result, all alerts were de-activated at the departure controller and ground controller's working positions) as well as how to operate the system including attention allocation techniques during aircraft takeoff and actions to deal with the subsystem messages and alerts;
- the porting of the screen second input of the A3000 A-SMGCS at the ATC shift supervisor WP for the display of the weather information that is not envisaged by the operational manual of the airfield surveillance and control subsystem. When weather information is selected to be displayed the radar data and the light alerts (which were present during the accident takeoff) become un available for the specialist that occupies the ATC shift supervisor's working position;
- the ATC shift supervisor's decision to join the sectors at working positions of Ground and Departure Control without considering the actual level of personnel training and possibilities for them to use the information of the airfield surveillance and control system (the criteria for joining of sectors are not defined in the Job Description of ATC shift supervisor, in particular it does not take into account the technical impossibility to change settings of the airfield surveillance and control system);
- failure by the ground controller to comply with the SOPs, by not taking actions to prevent the incursion of RWY 2 that was closed for takeoff and landing operations by the vehicles though having radar information and alert on the screen of the airfield surveillance and control system;
- failure by the out of staff instructor controller and trainee controller (providing ATM under the supervision of the instructor controller) to detect two runway incursions by the snowplow on the runway in use, including after the aircrew had been cleared to take off (as the clearance was given, the runway was clear), provided there was pertinent radar information on the screen of the airfield surveillance and control subsystem and as a result failure to inform the crew about the obstacle on the runway;
- lack of recommendations at the time of the accident in the Operator's (Unijet) FOM for flight crews on actions when external threats appear (e.g. foreign objects on the runway) during the takeoff;
- the crew failing to take measures to reject takeoff as soon as the Captain mentioned «the car crossing the road». No decision to abort takeoff might have been caused by probable nonoptimal psycho-emotional status of the crew (the long wait for the departure at an unfamiliar airport and their desire to fly home as soon as possible), which might have made it difficult for them to assess the actual threat level as they noticed the snowplow after they had started the takeoff run;
- the design peculiarity of the Falcon 50EX aircraft (the nose wheel steering can only be controlled from the LH seat) resulting in necessity to transfer aircraft control at a high workload phase of the takeoff roll when the FO (seated right) performs the takeoff.

In a report published in January 2013, the French BEA confirmed that the accident was the consequence of an excessive frost accretion on all surfaces and airframe of the airplane. Investigations were able to determine that the aircraft was flying at the limit of its performances in adverse weather conditions with dangerous phenomena such as the accretion of clear ice. This situation caused the frost alarm to activate, and the pilots to increase their altitude. At this moment, the airplane entered a spin and the tail detached due to aerodynamic forces that exceeded its certification/design. Out of control, the aircraft completed several barrels before breaking up and descending to the ground.

Left main gear collapsed upon landing for unknown reasons.