Transavia B738 over Balearic Sea on Sep 23rd 2016, turbulence injures 3 cabin crew

Last Update: June 20, 2018 / 15:02:52 GMT/Zulu time

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Incident Facts

Date of incident
Sep 23, 2016

Classification
Accident

Flight number
HV-5625

Aircraft Registration
PH-HXA

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Transavia Boeing 737-800, registration PH-HXA performing flight HV-5625 from Amsterdam (Netherlands) to Palma Mallorca,SP (Spain) with 184 passengers and 6 crew, performed the flight at maximum cruise level FL250. While enroute over the Balearic Sea, outside Spanish Airspace, several minutes before 13:00Z the aircraft encountered turbulence causing injuries to 3 cabin crew. The aircraft continued to Palma Mallorca for a safe landing. The 3 flight attendants were taken to a hospital with serious injuries.

The occurrence aircraft remained on the ground in Palma for 4 hours, then departed for the return flight HV-6512 to Eindhoven (Netherlands) climbing to a maximum cruise level FL240, but then diverted to Amsterdam.

The Dutch Safety Board (DSB) reported that the occurrence was rated an accident. Spain's CIAIAC reported that the accident happened outside Spanish Airspace over International Waters and did not open an investigation, therefore the DSB opened an investigation. The three cabin crew received serious injuries.

On Jun 20th 2018 the DSB released their final report concluding the probable causes of the accident were:

The accident happened because the cabin crew was not warned of possible turbulence and the fasten seatbelt sign was switched on only shortly before the aircraft encountered turbulence. The cabin attendants were not seated with safety belts fastened as they stood up to carry out their duties during unanticipated severe turbulence.

Contributing factors

The late appearance of the convective cloud on the weather radar was probably caused by a very quick development of this cloud in combination with its low reflectivity. There are no signs that the RDR-4000 weather radar did not function properly.

Known relevant and important weather information never reached the pilots because the briefing was prepared well in advance of the flight and was not updated by dispatch before the flight commenced.

Although the crew showed knowledge on the general risks of thunderstorms, the possible effects for the cabin crew and passengers of possible encounters with turbulence were not fully appreciated. Fatigue related aspects might have been a factor in this lack of appreciation.

The procedures of Transavia on how to deal with turbulence do not reflect the latest views of the industry, as reflected in a recent IATA study “guidance on turbulence management”. Preparing the cabin crew and passengers for unanticipated turbulence is not addressed in the company manuals.

The DSB reported that one of the air conditioning systems was inoperative, the aircraft therefore was not permitted to fly above 25,000 feet.

The DSB summarized the events on board:

The flight was uneventful until shortly before top of descent towards the airport of Palma de Mallorca. The flight crew visually spotted two thunderstorm clouds (Cb) which were also visible on the first officer’s weather radar screen. The captain had no weather radar data displayed at that time on his navigation display (ND). The position of the thunderstorms and their routing was such that they were of the opinion that they could fly between them to waypoint “LORES”, where the arrival route to LEPA started.

At 12.49:58 the purser entered the cockpit for a chat. At 12.59:56, the latest landing information of the airport of Palma de Mallorca (ATIS5 information C) was received via ACARS. The weather information included in this information, indicated thunderstorms in the vicinity of the airport, described as “cumulonimbus, thunderstorms without precipitation”. This information led to the remark that the descent might be a bit bumpy. The purser responded with the remark that ”basically they were ready“.

At 13.00:51 the first officer asked if he should “switch the ice on” which was affirmed by the captain. However, FDR data showed that the anti-ice was not switched on. At 13.01:03 it was noticed that the aircraft picked up some ice and the purser made the remark that some ice accumulated on the windshield wipers.

The flight entered clouds shortly before the aircraft crossed the coastline of the Spanish mainland just south of Gerona, around 13.01, and from that moment on the crew had to rely on their weather radar screens for information about the thunderstorms. At 13.02:17 the purser left the cockpit, some 7 minutes before the occurrence took place. After she had left, the expression “thunderstorms without precipitation” was discussed between the flight crew and this led to the remark that it possibly would cause extra turbulence during approach.

Around 13.03 the captain switched on his weather radar screen as well, in automatic mode. The range selected by the captain was 160 NM, and the first officer had 80 NM selected, in manual mode. The DSB was unable to establish the value of the altitude setting of the radar screen of the first officer because he could not remember if or how he changed the altitude settings. Both pilots did not change the gain setting of the weather radar. The distance to the airport was approximately 60 NM at that time. Neither pilot noticed any thunderstorms directly ahead, i.e. in the path of the aircraft, on their weather radar screens. The captain started the crew briefing with information from the EFB6 and the weather information as received via ACARS. At 13.04, about 5 minutes before the occurrence, the engine anti-ice protection was switched on again. Also the pilots discussed the cold weather operation and concluded that the current track was still good to fly in between the clouds visible on the weather radar.

Two minutes and 25 seconds before the occurrence, the captain switched his range of the ND back to 80 NM. The first officer had done so almost 4 minutes earlier, and now reduced his range further to 40 NM and subsequently, at 1,5 minutes before the occurrence, to 20 NM. No remarks were made between the pilots about thunderstorms or reasons for the range reduction as the crew briefing continued. At 13.08:37, 40 seconds before the occurrence, the first officer interrupted the captains crew briefing and suggested to maneuver clear of a small red return on their radar screens. The captain agreed and started a 30 degrees right turn in two steps from heading 185 to heading 215. The first officer, in the meantime, asked permission for this from ATC. This was granted immediately, and also instructions were given to descend to FL200. At less than 15 seconds before the occurrence, the captain, too, switched the range of his ND to 20 NM and at 13.09:09 he decided to switch on the ‘fasten seat belts’ sign. As the aircraft turned to the selected heading, a short burst of about 5 seconds of hail was encountered, with associated turbulence lasting 8 to 9 seconds. This happened at 13.09:17, almost 17 NM before waypoint LORES on airway UP84. The flight crew expressed their surprise about the severity of the encountered turbulence, and the captain decided to make a short announcement to the passengers regarding the turbulence.

After the ‘fasten seat belts’ sign was switched on, the three cabin attendants, who had been seated in the pantry in the back of the aircraft, all stood up; two with the intention to check if the passengers had fastened their seatbelts and one in order to check the pantry for any loose items. At the moment they got up, the aircraft encountered the turbulence. All three were smashed to the ceiling and thrown around the pantry, before falling on the floor. The cabin attendants were not aware of expected turbulence.

The purser was seated in the front pantry when the aircraft encountered the turbulence. She was lifted from her crew seat and landed on her crew seat again. She instructed the passengers immediately to take their seat and to fasten their seatbelts. It turned out that some passengers had not fastened their seatbelts during the turbulence. Some of them were also lifted from their seats and landed back on their seats. When the purser checked whether all passengers did follow the instructions, she was confronted with the situation in the aft pantry.

At 13.11:27 the purser then called the flight crew and told the pilots that “we have three people lying on the floor”.7 Three minutes later the purser called the cockpit again to inform the captain that the three cabin attendants had fallen during the occurrence and were not able to stand anymore. She also told the captain that one of the passengers, a doctor, was attending the injured cabin attendants, and that she needed more time to prepare the cabin for the landing. A minute later the captain informed ATC that the flight had encountered “heavy turbulence” and requested three ambulances upon landing as three cabin attendants were seriously injured.

The captain decided not to declare a mayday message because the purser needed more time to stabilize the situation. During the subsequent descent the flight crew circumnavigated several thunderstorms and asked for delaying vectors even though ATC indicated that they would get priority. Fifteen minutes later ATC asked if they needed only three ambulances or also “a doctor on board”. The crew affirmed the three ambulances and the need of a doctor. Two minutes later the purser reported that the cabin was prepared for landing, and that they were ready. At that moment the cockpit crew requested priority for landing and, again, confirmed the need for a doctor. An uneventful landing was made on runway 06L at Palma de Mallorca at 13.41:36.

The DSB analysed the weather situation:

Satellite images of the area of the accident show the build-up of clouds between the southeast coast of Spain and the island of Mallorca between 13.00 and 13.30. The two thunderstorm clouds seen by the flight crew are clearly visible. The images also show that between these two clouds, another cloud was quickly developing. This cloud developed in size, both horizontally and vertically. Furthermore, the dBz (indicator for number of drops per volume unit) also increased quickly. The blue color on the satellite image of 13.00 showed a low dBz; between 12 and 18. According to the RDR-4000 manual, this would result in no or a very low return. At 13.10 the dBz was increased to 30-42, which must have been visible on the ND. This was confirmed by the crew statements.

Shortly before the occurrence, hail was audible on the CVR. This hail was not visible on the weather radar in the form of a strong return. Thunderstorms with large amounts of wet hail return stronger signals than those with rain or dry hail. This suggests that the audible precipitation consisted of dry hail, and/or that the core of the hail shaft was very narrow. Also the meteorological information “cumulonimbus, thunderstorms without precipitation” that was received, indicated that these clouds contained no or little precipitation resulting in low reflectivity that could be detected by the weather radar. The difference between the satellite images of 13.00, 13.10 and 13.20, which was the time frame in which the occurrence happened, is a strong indication that this Cb was developing very quickly during that time. This indication is supported by satellite images of the height of this Cb: the height of its top increased between 13.00 and 13.10 from about 5-7 kilometers to about 10-12 kilometers, so it almost doubled in 10 minutes.

With respect to current SIGMETs the DSB analysed:

During flight crews are able to retrieve actual weather reports via ACARS, as they did with Palma and the alternate Menorca as well as a forecast, but no SIGMETS. The latter have to be transmitted to the aircraft, usually done by Dispatch. Although the issued SIGMETS must have been available to Dispatch, the crew was not informed about this.

According to the tasks of Dispatch, as described in operating Manual A and the OPC Handbook, only a weather check in advance of a flight, during flight preparations is required. Obviously, flight crews are therefore not provided with relevant weather changes or significant weather. According to Transavia procedures flight crews are expected to check that themselves or ask Dispatch to do so. Crews have no knowledge of the issuing of SIGMETS during flight, and can therefore not be expected to perform this task sufficiently. Especially in the case of significant weather, this might lead to dangerous situations.

...

Based on the SWC and weather reports available to the pilots, it was very difficult for the pilots to conclude that the medium and upper levels of the atmosphere were generally instable, and that this is characteristic of rapidly developing thunderstorms.

By not providing the flight crew with the latest weather updates, in particular SIGMETS, Dispatch and Spanish ATC missed an opportunity to warn the flight crew of developing thunderstorms present en route.


The DSB analysed that neither pilot used the gain control of the weather radar and wrote: "According to the Pilots Guide rotating the Gain knob to the maximum (MAX) position increases the sensitivity by approximately 10 dBz. When using different gain settings the presence of the quickly developing Cb could have been noticed in an earlier stage. Furthermore, the Pilot’s guide states: In manual mode, maximum gain is useful when looking at altitude slices above the freezing level where particles are less reflective."

With respect to pilot fatigue the DSB analysed:

Investigation established that both pilots had a small sleep loss, and operated close to the second circadian rhythm while none of the other fatigue factors were present.

The crew missed the signs that sudden turbulence might be present which could hint to effects of degraded vigilance and /or a degraded judgment. This decreased performance of the crew could have been the result of some degree of fatigue

The DSB analysed the flight data:

Between 13.09:14 to 13.09:18 the absolute vertical acceleration went from 1.00g to 1.97g, from 1.97g to -0.2g and from there to 1.66g. The changes between the three peaks, the forces to which the occupants were exposed, are respectively +0.97g; -2.17g and +1.86g. According to ICAO documents accelerations between 0.5g and 1.00g are considered moderate turbulence and accelerations greater than 1.00g are considered severe turbulence.

With respect to response by emergency services the DSB analysed:

Despite the crew’s request for three ambulances and a doctor only two ambulances showed up considerable time after landing of the aircraft. The first ambulance arrived approximately 10 minutes after landing, around 36 minutes after the first request, and it took another 15 minutes before the second arrived and eventually no doctor showed up.

It turned out that neither ambulances nor a doctor were available on the airport of Palma de Mallorca to provide medical assistance because of another medical emergency. The ambulances had to come from an off-airport hospital, which took a considerable amount of time. According to the Aerodrome Emergency Plan (AEP), the airport’s medical doctor must be available for coordination and organization of medical emergency services. In the AEP nothing is mentioned about the availability of ambulances. The DSB considers this not to be in accordance with EU Regulations as it speaks of “commensurate with the aircraft operations and other activities conducted at the aerodrome”.

...

Neither ambulances nor a doctor were present on the airport of Palma de Mallorca to provide medical assistance. If necessary adequate medical assistance and transportation must be available at very short notice under all circumstances.
Aircraft Registration Data
Registration mark
PH-HXA
Country of Registration
Netherlands
Date of Registration
AbejgpqcpAbce Subscribe to unlock
Airworthyness Category
Legal Basis
Manufacturer
The Boeing Company
Aircraft Model / Type
737-800
ICAO Aircraft Type
B738
Year of Manufacture
Serial Number
Aircraft Address / Mode S Code (HEX)
Maximum Take off Mass (MTOM) [kg]
Engine Count
Engine
JkcccfceemhchhkAjcphflbhmfbhfgdcilg Subscribe to unlock
Engine Type
Incident Facts

Date of incident
Sep 23, 2016

Classification
Accident

Flight number
HV-5625

Aircraft Registration
PH-HXA

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

This article is published under license from Avherald.com. © of text by Avherald.com.
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