Description

On 18 October 2011, a Boeing 777-300 being operated by Etihad Airways on a scheduled passenger service from Manila, Philippines to Abu Dhabi UAE with an augmented flight crew encountered severe turbulence in the cruise in night Instrument Meteorological Conditions (IMC). Two serious injuries and 12 minor injuries were sustained by the occupants as a result and some superficial impact damage occurred to the passenger cabin internal trim.

Investigation

The Incident occurred in international waters and the Investigation was conducted by the Air Accident Investigation Sector (AAIS) of General CAA of the State of the Operator, the UAE. The failure of the aircraft operator to notify the event to the GCAA resulted in the relevant Cockpit Voice Recorder (CVR) recording having being overwritten by the time the unit was removed but DFDR and QAR data was successfully obtained. In respect of the 2 hour CVR, it was also found that in apparent breach of regulatory requirements, it was only capable of recording the area channel for that period and the four separate channels for only 30 minutes.

It was noted that the aircraft commander had completed his upgrade to a first command less than three months previously and that the Operating First Officer was making only his fourth flight following release from type conversion training for unrestricted operation on the aircraft type.

It was found that the Captain had left the flight deck to take a comfort break leaving the operating First Officer as PF and the second First Officer, who was not qualified as a cruise relief pilot “assisting”, initially from one of the supernumerary crew seats before moving temporarily to the left hand seat. It was noted that the cruise relief pilot was not qualified as a cruise Captain.

At the onset of the initial light turbulence the Captain was in a lavatory and had subsequently walked around the cabin. When the severe turbulence began, he had been in the business class cabin and had managed to secure himself in one of the vacant seats there until the turbulence subsided.

It appeared that the aircraft had been clear of cloud prior to the event but an isolated Cumulonimbus (Cb)(Cb) build up had been observed approximately 20 nm ahead - approximately 2 minutes flight time - on track. After some confusion in R/T communications and “a contributory CPDLC uplink delay” which had distracted both pilots, the aircraft course was altered to the right so that the cell was being passed at a range of about 7nm. When abeam of the cell, severe turbulence had occurred for approximately 45 seconds during which the aircraft climbed approximately 600 feet and the stick shaker activated. Recovery was eventually achieved with the cleared level regained and the AP re-engaged but not before a second stick shaker activation had occurred. DFDR data showed vertical accelerations ranging between +1.98g and -0.68g during the excursion and the two stick shaker activations occurring as angle of attack exceeded 6° during high positive ‘g’ loading.

The Captain had not returned to the flight deck until after the event occurred, having taken refuge in a vacant seat in the business class cabin. During the turbulence, the majority of the passengers were in their seats with their seat belts fastened but one was in a toilet compartment and another was exiting one. The former sustained serious injuries.

Based on the witness statements, it appears that the seatbelt sign had been switched on approximately 10 minutes prior to the incident during some minor turbulence. An announcement was made in Arabic and English advising passengers to fasten their seatbelts. However, some belts, including those used by passengers who were subsequently injured, were only ‘loosely fastened’.

A total of seven passenger injuries were detailed by the Investigation. It was found that most of the injured passengers had been seated with their seat restraints fastened. It was noted that after the cabin crew had ‘secured the cabin’, two passengers had nevertheless visited mid cabin toilet compartments. One was in such a compartment when the severe turbulence started and was thrown up the ceiling and then fell down onto the floor. This person had been seriously injured and was subsequently secured on the floor of the adjacent galley by cabin crew. The other of these passengers was returning to their seat when the severe turbulence started and sustained injuries after being thrown against cabin fixtures before managing to reach their seat. Four other passengers impacted the PSU’s above their seats despite reportedly having their seatbelts “loosely fastened”. Several oxygen masks were deployed and the PSUs were damaged as a result of these impacts. One other passenger was reported to have sustained injuries after being “ejected from their seat” and hitting an exit door handle.

During the turbulence, no cabin services were being conducted and subsequently all the carts and containers were stowed in their original stowage which remained intact due to the presence of latches in the locked position. However, it was found that despite the requirement for all passengers to secure themselves prior to the turbulence encounter, none of the twelve cabin crew had been similarly secured and many had been “involved in galley activities”. Of the seven who had been in the various galley areas, six sustained minor injuries and one sustained serious injuries. Two cabin crew who had been in toilet compartments were stated to have sustained minor injuries but both eventually managed to exit these compartments and secure themselves in the nearest available crew seats. Two in the upper crew rest compartment were thrown upwards from their bunks and hit the ceiling but as the compartment ceiling is low, they fell back down onto the mattresses on which they had been lying thus minimising the impact. The Cabin Manager had been seated unsecured in the forward left cabin crew seat and was thrown from the jump seat and fell to the floor before managing to regain the seat and secure herself. All injured cabin crew were reported to have required post flight medical attention.

Given the cumulative effect of multiple cabin crew sustaining various degrees of injury, the Investigation considered that Operator guidance on how to respond to such a scenario was not adequately covered in existing documentation and “a further definition of Cabin Crew Incapacitation relating to the ability to carry out the defined cabin crew safety functions with several cabin crew injured should be reassessed.”

It was noted that the pre flight weather briefing material had indicated the likelihood of encountering embedded Cumulonimbus (Cb) on the planned track over the Bay of Bengal and that such a situation was typical of the southward movement of the Inter Tropical Convergence Zone (ITCZ) in the northern winter.

The Investigation documented Findings on Crew Competence as follows:

• The Flight Crew were unfamiliar with the use of the Weather Radar
• The two First Officers were unfamiliar with CPDLC and Datalink procedures
• The Flight Crew employed non standard procedures in respect of cabin safety communications prior to turbulence
• The Flight Crew were not familiar with the requirements for flying offset tracks or with weather deviation procedures in Reduced Vertical Separation Minima (RVSM) airspace if a revised ATC clearance cannot be obtained.
• the Cabin Crew failed to adhere to prescribed SOPs for Turbulence Safety and in particular failed to ensure that cabin crew and passengers were secured in their seats during turbulence.

Having accepted that the cause of the occupant injuries and cabin trim damage was the encounter with severe turbulence, the Investigation concluded that a combination of Flight Crew factors contributed to the late track deviation:

• Inadequate crew coordination
• Inadequate Crew Resource Management
• HF Communications difficulties
• The absence of the Captain from the flight deck during the FIR transition and subsequent radio communication problems.
• The late recognition of the adverse weather on the weather radar
• The Captain’s delayed return to the flight deck immediately after the severe turbulence encounter (affected) the normalisation of the CRM environment.

It was also concluded that the Cabin Crew had contributed to the severity of the consequences of the turbulence encounter by:

• Not effectively monitoring the passenger use of the lavatories when the seat belt sign has been switched on.
• Performing routine cabin crew organisational duties when the seat belt sign is on in the galley and associated areas.

The failure to identify the incident as ‘Category B’ event in accordance with the Etihad Emergency Response Procedures Manual, which was found to give an example of such an event as violent and extreme air turbulence resulting in serious injury to one or more persons, was noted. It was observed that “the appropriate categorisation would have activated the Emergency Response Centre with all the necessary resources involved in the assistance to the passengers, coordination with the investigative authorities and recovery of the operations”.

Ten Safety Recommendations were made as a result of the Investigation as follows:

• The Aircraft Operator should review their internal procedures for the immediate notification of Accidents/Serious Incidents to the GCAA Duty Investigator.
• The GCAA should revise CAR Part IV, CAR-OPS 1.700 (b) for large passenger aircraft operators to specifically mandate the requirement for 4 channel uncombined/non mixing CVR LRU’s.
• All Aircraft Operators using pooled CVR procedures involving the L3 FA2100 CVR should ensure that all CVRs should be MOD-DOT #7 modification compliant pending a revision of GCAA CAR Part IV, CAR-OPS 1.700 (b).
• The Aircraft Operator should develop procedures which prevent maintenance engineering or the maintenance provider from tampering with flight data recorders either inadvertently or otherwise. This procedure shall be robust and form part of the notification to the GCAA DI as in the first Recommendation.
• The Aircraft Operator should review the policy for activation of the Emergency Response Plan (ERP) where there are passenger and crew injuries requiring medical intervention.
• The Aircraft Operator should determine an emergency procedure to manage several injured cabin crew following a major severe turbulence event and develop an acceptable contingency policy to mitigate the risks.
• The Aircraft Operator should ensure that its Training & Standards Department reviews the training and re-currency requirements for the following:
  • the training syllabus for the use of weather radar.
  • the training syllabus for the operational use of CPDLC and other Data link communications.
  • the provision of user guide material to pilots on weather radar and CPDLC operational usage.
  • the provision of pilot guidance material on weather deviation procedures in RVSM airspace.
  • the Human Factors Training policy and the Crew Resource Management dynamic management and decision making procedures when the Captain is not on the flight deck.
  • current cabin security procedures during turbulence for service level 1, 2 and 3.
  • the management of Interruptions and Distractions [Coping with unexpected distraction, disturbance and contingency in the cockpit requires the use of techniques to lessen the effects of any disruption in the flow of on-going cockpit activities].
  • Threat and Error Management (TEM) (TEM) Techniques specific to adverse weather.
• The Aircraft Operator should introduce a procedure for managing reduced mobility/injured cabin crew as result of an in-flight safety events which affect the cabin crew fitness to operate if the (number of) cabin crew (on board) is less than the minimum required for the aircraft type.
• The Aircraft Operator should ensure that cabin crew adhere to the turbulence procedures which require them to secure themselves and the passengers as CCM SEP 7.3.5 Manual/OM-A 8.3.12.
• The Aircraft Operator should re-emphasise the turbulence procedures for passenger safety in respect of the use of lavatories and the use of seatbelts during turbulence events.

The Final Report of the Investigation was made available in late 2012.

Further Reading

• Monsoon
• Turbulence
• Situational Awareness
• Weather Radar: Storm Avoidance