B738, en-route, near Cuneo northwest Italy, 2021
B738, en-route, near Cuneo northwest Italy, 2021
On 25 July 2021, a Boeing 737-800 which had previously been manoeuvring visually around storm cells over the Alps during the initial descent into Nice turned back on track believing the avoidance action was complete but was then unable to avoid penetrating a further cell during which severe turbulence caused a serious injury to one of the cabin crew and a lesser injury to another. Multiple aircraft in the area had been simultaneously requesting track deviations at the time with ATC displays not showing weather returns. In the absence of plans to introduce this, a corresponding safety recommendation was made.
On 25 July 2021, a Boeing 737-800 (SE-RPE) being operated by Norwegian Air Sweden on a scheduled passenger flight from Copenhagen to Nice as NAX 3646 was unable to avoid briefly penetrating a storm cell during a descent previously conducted in day VMC. One unsecured member of the cabin crew sustained a serious injury and another a minor one. The flight was completed without further event and landed at its destination twenty minutes later where both injured cabin crew were taken to hospital.
An Investigation was carried out by the French Civil Aviation Accident Investigation Agency, the BEA, using relevant FDR and CVR and recorded ATC data. No information on pilot or controller experience was recorded but the Captain was recorded as having been PF. It was noted that:
- the actual weather conditions experienced during the second half of the flight were in line with the significant weather chart valid for the time.
- aircraft weather radar settings are not saved in the FDR and it was therefore not possible to determine its configuration during the flight.
- Milan ACC controllers did not have weather radar returns on their screens and “there are currently no plans to change this”.
On transfer to Milan ACC whilst still in the cruise at FL 370, the flight reported being on a southerly heading to avoid storm cells and the controller responded by asking for notification when the flight was able to proceed directly to the ‘BORDI’ waypoint. The crew acknowledged this request but noted that “there were Cb clouds ahead, over a distance of 80 nm". After one minute, the flight requested a deviation 20° onto 215° to the right for weather avoidance (point 1 in the first illustration below) which was approved.
After around five minutes, the flight was transferred to a different sector and on advising their weather avoidance heading were asked to report ready to turn left for FPL waypoint ‘BORDI’ which the crew estimated would be in about another 40nm. A couple of minutes later, the controller asked if the flight was now able to begin tracking direct to ‘BORDI’ and on receiving an affirmative response, the flight was transferred to another Milan ACC control sector.
On checking in with the new frequency and accepting re-clearance to FL340, the flight confirmed that it was now able to turn back towards the ‘BORDI’ waypoint and was so cleared and transferred to yet another sector where further successive descent re-clearances to FL 310, FL 270 and finally FL 170 were given with a request to be at FL270 before reaching ‘BORDI’ (point 4 in the first illustration below). After a further five minutes, it became clear to the crew that another deviation to the right would be necessary and a request for 20° to the right was made and approved (point 5 in the first illustration below) subject to stopping the descent at FL 210. Following a subsequent request from the controller as to how long this heading deviation would be required for, the crew responded with “a further 10nm”.
After two minutes on this deviation, the flight advised that it was again able to turn left towards ‘BORDI’ (point 7 in the second illustration below) and this was approved, again with a requirement to descend to FL 170 and be at this level on reaching.
The ground track of the flight final 50 minutes of the flight. [Reproduced from the Official Report]
A close up of the ground track where the storm cell was entered against a rainfall radar recording. [Reproduced from the Official Report]
Almost immediately this left turn had been made, the Captain observed the appearance of a new storm cell ahead and remarked “this one will make a bang” adding that he had put the ‘Fasten Seat Belt’ sign on. He then called “engine anti-ice on” and almost immediately (point 8 in the second illustration below), a sudden background noise was recorded, indicative of the impact of sudden heavy precipitation on the windshields.
A pronounced and rapid fluctuation in both airspeed and vertical acceleration followed accompanied at one point by an uncommanded roll which was sufficient to trigger a EGPWS ‘BANK ANGLE’ Alert which caused the Captain to disconnect the AP. After 25 seconds, the noise of rain on the windshields ceased and the Captain was recorded as saying “and now we are out” with all turbulence ceasing a few seconds later (point 11 in the second illustration below).
Twenty seconds later, passing approximately FL210, the flight was transferred to Nice APP and the Captain received a cabin crew injury report and an ambulance to meet the flight on arrival was arranged. Twenty minutes later the aircraft landed off an RNP approach at Nice.
The Investigation was concerned at the absence of weather radar returns available as a background on the ATC controller displays, noting that the situation and no plan for rectification also applied in France where a previous related Safety Recommendation relating to a 2013 Serious Incident had not been followed by any action.
The following new Safety Recommendation was therefore made:
- that the European Union Aviation Safety Agency in coordination with EUROCONTROL:
- Conduct a global review of existing systems and those being developed that display near-real-time weather images on the radar screens of air traffic controllers and their use by Air Navigation Service Providers as part of the flight information service, with the aim of facilitating meteorological avoidance strategies developed by flight crews.
- On the basis of the above review and other available data, identify the system specifications, tools and working methods that would be most suitable for use by European Air Navigation Service Providers in order to facilitate weather avoidance strategies developed by flight crews.
The Final Report was published simultaneously in English translation and in the definitive French language version on 17 October 2022.