Description

On 22 October 2009, a Britten-Nornan BN2A Islander (PJ-SUN)being operated by Divi Divi Airlines on a scheduled passenger service from Curaçao to Bonaire in day Visual Meteorological Conditions (VMC) experienced a failure of the right engine as it reached cruise altitude. The Pilot attempted to complete the intended flight but when altitude could not be maintained he was eventually forced to carry out a ditching within a few miles of the destination. Four of the nine passengers received minor injuries but all were able to exit the aircraft before it sank in deep water. Attempts to release the Pilot who was trapped and had been rendered unconscious by the effects of the impact were unsuccessful.

Investigation

An Investigation into the accident was initially commenced by the Directorate of Civil Aviation Netherlands Antilles (DCANA) but on 17 November 2009 the Dutch Safety Board (DSB) received a request from the of the Ministry of Traffic and Transport of the Netherlands Antilles to take over the Investigation and began work immediately. The DSB Investigation sought to established the full circumstances of the accident as well as carry out a review of the emergency services response to it. It was noted that the aircraft was not required to be fitted with either a Cockpit Voice Recorder (CVR) or Flight Data Recorder (FDR), nor had it been so fitted. However recorded radar data showing the progress of the flight was available.

It was noted that the Pilot had achieved his first command relatively recently on the BN2 Islander having gained most of his commercial multi-engine flying experience as a Co-pilot on the DE HAVILLAND CANADA DHC-6 Twin Otter undertaking similar VFR operations to the ones he was now flying on the Islander.

It was established that the aircraft had taken off from Curaçao for Bonaire with all ten seats occupied including the one next to the pilot. Climb to a cruising level of FL035 for the overwater flight to Bonaire had proceeded normally, but when the pilot throttled back to cruise power upon reaching this level, the right engine had failed. After unsuccessful attempts at a restart, the pilot had been observed to feather the failed engine propeller and maintain directional control by use of rudder. Despite the failure occurring whilst the aircraft was still over or very near land - and only about a quarter of the way along the planned route - the Pilot continued the flight towards Bonaire. It was found that although the flight was VFR and the cruise altitude was therefore at the discretion of the Pilot, the normally chosen cruise altitude was 2000 feet. Although no reason for this decision could be determined, the Investigation did find circumstantial evidence in the form of irregularities in the loadsheet prepared by the pilot for the flight which indicated that he may well have been aware that the aircraft was overloaded - the Investigation view on this subject was stated as:

“The ninth passenger and the values for the baggage, cargo and fuel weights were not shown on the load and balance sheet filled in by the pilot…..and the only possible explanation for this is that filling in the weight of the ninth passenger and the correct baggage, cargo and fuel weights would have made the total take-off weight on the sheet higher than 6600 lb. This would have been reason for keeping the aircraft on the ground as it would have exceeded the (absolute maximum) weight limit of 6600 lb that was being applied by Divi Divi Air. The supposition is justified that the pilot must have been aware that the aircraft was being overloaded.”

As the flight progressed, it became apparent that altitude could not be maintained on one engine - radar data (see the diagram below) showed that the aircraft descended at an average rate of approximately 140 fpm from the moment the engine failed until the ditching. Eventually, approaching Bonaire, it became obvious that a ditching would be inevitable. This was performed without flaps set and with the stall warning system sounding as impact with the water approached. Contact with the water resulted in the left front door being torn off such that the cabin rapidly filled with water. However all nine passengers were able to exit the aircraft and formed a group in the water with those wearing life jackets supporting those who were not. The Pilot was trapped in his seat by the distortion of the front of the aircraft caused by the impact and had also hit his head on the cabin structure and been knocked unconscious. Despite efforts by passengers to release him, he was still trapped and apparently unconscious when the aircraft sank shortly afterwards and according to the subsequent post mortem died from drowning.

The Investigation found that although there was no specific ditching procedure in the Aircraft Flight Manual (AFM), instructions for ditching were included in the Divi Divi Air General Operating Manual. These stated that in order to minimise impact forces by landing at as low a speed as possible, the flaps should be selected their maximum setting for any ditching with one engine inoperative. These instructions also stated that “a stall situation should be avoided because it will result in uncontrolled impact with the water surface:. Corresponding pilot training was found to have been provided on these points. In was additionally established that Company Pilot Line Training emphasised that on the Curaçao to Bonaire route, a return to Curaçao should be made “even when engine problems occur past halfway (point) due to the prevailing eastern trade wind, the better landing options on the east coast of Curaçao and the better technical and assistance facilities on Curaçao”.

The reported deformation of the front of the aircraft structure caused during the ditching was confirmed following the recovery of the wreckage – see the illustration below:

In respect of the weight of the aircraft, it was found that on the instructions of the pilot the accident aircraft had been refuelled prior to departure to full tanks. Although it was noted that the Britten-Norman Islander fuel type was not available in Bonaire and so return fuel had to be carried, it was found that a maximum fuel load was sufficient for three return flights on the high frequency service on the Curaçao - Bonaire route and that Pilots often uplifted fuel sufficient for multiple return flights in order to save time.

Despite every attempt being made, it proved impossible for the Investigation to determine why the right engine had malfunctioned. On this subject, the Investigation noted that disassembly and examination of both recovered engines found no indications that parts had overheated or suffered from insufficient lubrication and there were no traces of extraordinary wear and tear. Overall, it was considered that both engines had been in good condition. The magnetos and carburettors were too corroded after seawater immersion to be functionally tested but no mechanical problems were found to indicate that the engines were not capable of producing power.

It was concluded that the left engine was still providing high power up to the ditching. From the statements of the passengers in respect of the attempted restarting of the right engine following its failure, it could be concluded that it did not stop due to an engine seizure and that this conclusion was supported by the absence of any indications of overheating or lack of lubrication of engine parts.

The main focus of the Investigation became what was soon discovered to have been the systemic failure of Divi Divi Air to operate safely and a concomitant systemic failure of the system of Regulatory Oversight to resolve this situation. Although there had not been significant consequences of this in the investigated accident, there were also concerns at the apparent fitness for purpose of the available emergency response ‘system’.

The Investigation concluded that the three Causal Factors which had contributed to the accident were:

• After one of the two engines failed, the flight continued to Bonaire. By not returning to the nearby situated departure airport, the safest flight operation was not chosen – continuing to fly after engine failure was contrary to the general principle for twin-engine aircraft as set down in the Civil Aviation Regulations for the Netherlands Antilles (CARNA) which is to land at the nearest suitable airport.

• The aircraft could not maintain horizontal flight when it continued with the flight and an emergency landing at sea became unavoidable - the aircraft departed with an overload of 9% when compared to the maximum structural take-off weight of 6600 lb. The pilot who was himself responsible for the loading of the aircraft was aware of the overloading or could have been aware of this. A non-acceptable risk was taken by continuing the flight under these conditions where the aircraft could not maintain altitude due to the overloading.

• The pilot did not act as could be expected when executing the flight and preparing for the emergency landing - the landing was executed with flaps up and, therefore, the aircraft had a higher landing speed - the pilot failed to ensure that the passengers had understood the safety instructions after boarding and made insufficient attempts to inform passengers about the approaching emergency landing at sea after the engine failure so that they were unable to prepare themselves sufficiently.

The following three Contributing Factors were also identified:

• Divi Divi Air management paid insufficient supervision to the safety of, amongst others, the flight operation using Britten-Norman Islanders. This resulted in insufficient attention to the risks of overloading. Findings in respect of this factor were formally stated as:
  • Although the maximum structural take-off weight of 6600 lb was used as limit during the BN2 flight operation of Divi Divi Air was accepted by the oversight authority, formal consent had not been granted for this.
  • A standard average passenger weight of 160 lb was in use for BN2 load and balance sheets whilst the actual average passenger weight was significantly higher. This meant that passenger weight was often lower on paper than was the case in reality.
  • A take-off weight of exactly 6600 lb completed on the load and balance sheet had occurred in 32% of a survey of these inter island BN2 flights conducted during the investigation. This is considered to be a strong indication that the luggage and fuel weights completed were incorrect in these cases and that, in reality, the maximum structural take-off weight of 6600 lb was exceeded.
  • Exceedances of the maximum structural landing weight of 6300 lb occurred in 61% of the same survey of inter-island flights.
  • The exceedance of the maximum allowed take-off weight had been recorded for all three of the Britten-Norman Islander aircraft in use and with different pilots.
  • Insufficient attention had been paid to aircraft weight limitations during training.
  • Lack of internal supervision with regard to the load and balance programme.
  • Combining management tasks at Divi Divi Air, which may have meant that insufficient details were defined regarding the related responsibilities.

• The safety equipment and instructions on-board the Britten-Norman Islander aircraft currently being used were not in order. Findings in respect of this factor were formally stated as:
  • Due to the high noise level in the cabin during the flight it is difficult to communicate with the passengers during an emergency situation.
  • The safety instruction cards did not include an illustration of the pouches under the seats nor instructions on how to open these pouches. The life jacket was shown with two and not a single waist belt and the life jackets had a different back than the actual life jackets on-board.

• The oversight of the Netherlands Antilles DCA (currently the Curaçao CAA) of the operational management of Divi Divi Air was insufficient in relation to the AOC authorisation for use of the Britten-Norman Islander aircraft. Findings in respect of this factor were formally stated as:
  • The operational restrictions that formed the basis for using 6600 lb (as a MTOW) were missing in the AOC, in the C of A of the accident aircraft and in the approved General Operating Manual of Divi Divi Air. The restrictions require flight only during daylight, under VMC and when a route is flown from where a safe emergency landing can be executed in case of engine failure.
  • The required (demonstrable) relationship between actual and assumed average passenger weights used for drawing up the load and balance sheet was missing.
  • The failure of Divi Divi Air’s internal supervision system for the load and balance programme.
  • Not noticing deviations between the (approved) safety instruction cards and the life jackets on-board during annual inspections.
  • The standard average passenger weight of 80kg set after the accident offers insufficient security that the exceedance of the maximum allowed take-off weight of flights with Antillean airline companies that fly with the Britten-Norman Islander will not occur.

Finally, three Other Factors identified as a result of the Investigation as follows:

• he recording system used for the radio communication with Curaçao TWR does not record the actual time so that the Investigation could not accurately determine the timeline related to TWR radio communications.
• The alerting and the emergency services on Bonaire were poorly coordinated and therefore did not operate optimally. Findings in respect of this factor were formally stated as:
  • The incident site command that should have taken charge of the emergency services in accordance with the Bonaire Island Territory crisis plan was not formed.
  • Insufficient multidisciplinary drills had been organised and assessed for executive officials who have a task to perform in accordance with the Bonaire island territory accident crisis plan. They were, therefore, insufficiently prepared for their task.

• The fire service and police boats could not be deployed promptly after the accident.

The Investigation noted the following Safety Action taken as a result of the Accident:

(1) The Directorate of Civil Aviation of the Netherlands Antilles:

• introduced a requirement for all Antillean airline companies flying the Britten-Norman Islander aircraft to base their load sheets on the actual weight of passengers and their hand luggage. Following consideration of data collected during the initial application of this requirement, a new standard weight of 80kg per adult was set for use as an alternative means of calculating the total weight of passengers and their hand baggage.

• complied an inventory of the different types of Britten-Norman Islander in the Netherlands Antilles and their various limiting weights, including the climb-limited take-off weight.

(2) Divi Divi Air:

• introduced a maximum of nine people including the pilot permitted on board each BN2 flight.

• introduced passenger weighing at both Curaçao and on Bonaire on 5

November 2009 and subsequently, as permitted, changed to the new 80 kg standard weight after CAA consideration of the results of this had been sent weekly to the Directorate of Civil Aviation (DCA) for three months.

• has stopped the carriage of newspapers on the first (BN2 operated) flight of the day.
• a maximum refuelling (at Curaçao) to half full after every return flight.

• The maximum allowed take-off weight has been reduced to 6300 lb.

• the standard altitude between Curaçao and Bonaire will now be 3500 feet and the standard altitude for the return to Curaçao will now be 4500 feet.

• It is now required that a check is performed to ensure that passengers are briefed by ground staff and the pilot to ensure completeness.

• All Britten-Norman Islander Safety Instruction Cards have been changed and replaced.

• The Safety Instructions Card is now also shown at the check-in desk.

• The load and balance sheet has been improved and replaced.

• Pilots have received instruction regarding the proper use of the load and balance sheet.

• In future heavier passengers will occupy the four front seats. If the ground staff cannot place the heavier passengers at the front of the aircraft at check-in, the pilot will explain it is better for the aircraft centre of gravity.

• The remaining two Britten-Norman Islander aircraft currently being used have been checked on possible damage as a result of exceeding the maximum structural landing weight. No defects have been found.

Four Safety Recommendations were made as a result of the Investigation:

• that Divi Divi Air should demonstrate to the Curaçao Civil Aviation Authority that the load and balance programme, the pilot training, the safety equipment and instructions of the Britten-Norman Islander aircraft in use are brought up to standard and complies with the legal requirements, and the limitations specified by the aircraft manufacturer, and that the risks of the load and balance programme are chartered and structurally controlled in the safety management system.

• that the Minister of Traffic, Transport and Division of Urban Planning and Housing of Curaçao should ensure that the Civil Aviation Regulations for the Netherlands Antilles (CARNA) are correctly applied and the user specifications by the manufacturer of the Britten-Norman Islander are being applied at airlines that fall under the supervision of the Curaçao Civil Aviation Authority in light of the findings (on operator oversight).

• that the Minister of Traffic, Transport and Division of Urban Planning and Housing of Curaçao should provide the Dutch Secretary of State for Infrastructure and Environment, being the responsible member of the government for Kingdom Affairs , the follow-up status of the ICAO audit 2008 findings in relation to the findings in this report.

• that the Governor of Bonaire, in respect of his responsibility for the support services and the emergency services, should ensure that the alerting process and the emergency (supporting) services are improved by regularly practising with deployment of multiple disciplines, assessment of this practice and taking measures to deal with any shortcomings that may arise.

The Final Report of the Investigation was published on 17 May 2011

Further Reading

• Loss of Control
• Ditching: Rotary Wing Aircraft
• Engine Failure After TakeOff - Light Twin Engine Aircraft
• Passenger Cabin Loading
• Aerodynamic Stall Awareness and Avoidance
• Pilot Workload
• Decision Making
• Continuation Bias