REPUBLIC OF KENYA MINISTRY OF TRANSPORT AND COMMUNICATIONS CIVIL AIRCRAFT ACCIDENT REPORT TRANSWORLD SAFARIS KENYA LIMITED

Transcription

1 REPUBLIC OF KENYA MINISTRY OF TRANSPORT AND COMMUNICATIONS CIVIL AIRCRAFT ACCIDENT REPORT CAV/ACC /6/00 OPERATOR: AIRCRAFT: REGISTRATION: PLACE: TRANSWORLD SAFARIS KENYA LIMITED LINDSTRAND LBL 260A BALLOON 5Y-BLK MARA SAROVA LODGE BALLOON LAUNCHING SITE DATE: 12 TH JULY TIME: 0330 HOURS ALL TIMES IN THIS REPORT ARE UTC ACCIDENT INVESTIGATION BRANCH P.O. BOX NAIROBI TELEPHONE: FAX:

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3 TABLE OF CONTENTS SYNOPSIS FACTUAL INFORMATION HISTORY OF THE FLIGHT INJURIES TO PERSONS DAMAGE TO THE AIRCRAFT OTHER DAMAGE PERSONNEL INFORMATION AIRCRAFT INFORMATION METEOROLOGICAL INFORMATION AIDS TO NAVIGATION COMMUNICATION AERODROME FLIGHT RECORDERS WRECKAGE AND IMPACT INFORMATION MEDICAL AND PATHOLOGICAL INFORMATION FIRE SURVIVAL ASPECTS TEST AND RESEARCH ADDITIONAL INFORMATION NEW INVESTIGATION TECHNIQUES ANALYSIS CONCLUSION FINDINGS CAUSE SAFETY RECOMMENDATIONS

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5 SYNOPSIS The balloon was being prepared for a flight, in the morning of 12 th July The flight was to be for the one pilot and his four passengers. The pilot had conducted the pre-flight checks which included checks for gas leaks, loose ropes and condition of the balloon envelope. The pilot had thereafter, instructed balloon attendants to inflate the balloon envelope with cold air which was done using three fans. On completion of the cool inflation, the pilot instructed the attendants to connect the on ground hot inflation cylinders. The hot inflation cylinders used by the operator were normally filled with butane liquid petroleum gas (LPG). When the pilot put a light to the burner, the cylinder exploded and fragments from the exploding cylinder hit him, killing him instantly and injuring some attendants and passengers. A fire started at the burners, setting on fire the balloon basket. The hot gases from the fire caused the balloon to float into the air and drift in the wind for a distance of about one kilometer, gaining a height of approximately 500 feet. The balloon finally crashed to the ground about one kilometer from the launch site. The contents of the basket were completely destroyed by the fire. 5

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7 1. FACTUAL INFORMATION The balloon had been prepared for a routine flight that was expected to last about one hour. The inflation cylinders -as was the routine- had been filled the night before. Operation of the cylinders required that they be filled with LPG as the fuel and nitrogen gas under pressure for use in pressurised gas discharge to the burners. The balloon attendants had left the lodge before the pilot and the passengers for the launch site which was about three kilometers from the lodge. They prepared the balloon in readiness for the pilot s preflight inspection. The preparation involved attaching all the ropes, basket and gas cylinders as well as spreading the envelope on the ground. The pilot arrived with the passengers shortly after and proceeded to carry out his pre-flight inspections. Once the pre-flight inspection was completed, he instructed the attendants to start the fans for cold inflation of the balloon, which they did. On completion of the cold inflation, the pilot instructed the attendants to connect the hot ground inflation cylinders which they did. He then selected the ground hot inflation cylinder and put a light to the burner. There was an immediate explosion which killed him instantly and injured some of the attendants. A fire started at the burners and some of the attendants and passengers suffered fire injuries. The balloon floated into the air due to the presence of hot gases and drifted in the wind for a distance of about one kilometer before crashing to the ground. The balloon was destroyed by the fire. The basket, the envelope and the gas cylinders were completely destroyed by the fire. All the pressure relief valves fitted to the cylinders blew and released the liquid petroleum gas held in the cylinders into the fire.

8 The injured were taken to hospital in Nairobi and the accident reported. Investigations commenced immediately. The air accident investigation branch of the United Kingdom was notified of the accident as the balloon was manufactured in the United Kingdom. 8

9 1.1. HISTORY OF THE FLIGHT Preparations for the flight had been done on the evening before the flight. These preparations included the filling of inflation cylinders, pressurising the cylinders and booking of passengers. The attendants left the lodge early in the morning before the pilot and his passengers, taking with them the balloon and all the accessories required for the flight. The pilot and his passengers followed shortly after to the launching site. The pilot carried out the pre-flight inspection including a check for gas leaks, entangled ropes and condition of the envelope. After completing the pre-flight checks the pilot proceeded with the cold inflation, followed by preparations for hot ground inflation. On putting a light to the burner of the ground hot inflation cylinder, there was an immediate explosion of the ground hot inflation cylinder which killed the pilot instantly. A fire started, injuring some of the attendants and passengers. The balloon caught fire and floated into the air, to a height of approximately 500 feet. It drifted in the wind finally crashing to the ground about one kilometer from the launching site. The balloon was completely destroyed by the fire. 9

10 1.2. INJURIES TO PERSONS INJURIES CREW PASSENGERS OTHERS FATAL SERIOUS MINOR DAMAGE TO THE AIRCRAFT The balloon was completely destroyed as a result of fire. The ground hot inflation cylinder exploded into fragments following the pilot s attempt to put a light to it. The balloon basket was completely destroyed by the fire and impact from the exploding cylinder. The envelope was also destroyed by fire. The other cylinders that were in the basket did not explode but their pressure relief valves blew as a result of the high temperature from the fire, releasing the liquid petroleum gas in them. These gases contributed in sustaining the fire OTHER DAMAGE None 10

11 1.5. PERSONNEL INFORMATION The pilot was a male British citizen aged 45 years. He held a Kenya pilot licence number YK-1882-CL(B) issued on the 16 th November His medical was valid from 18 th April 2000 and was expiring on 17 th October At the time of renewing his licence on the 19 th April 2000, his total flying experience was 2816 hours. All the experience was on hot air balloon flying AIRCRAFT INFORMATION The balloon was manufactured by Lindstrand Balloons Limited of the United Kingdom in The model was LBL260A, serial number 385. It was first issued with a certificate of airworthiness for export number E047721/001 by the United Kingdom Civil Aviation Authority on the 2 nd August 1996 and was subsequently exported to Kenya. The balloon was first registered in Kenya as 5Y-BLK on the 22 nd August 1996 and issued with a certificate of registration number The balloon also held a certificate of airworthiness number 1791 issued on the 5 th September The certificate of airworthiness was due to expire on the 22 nd March According to maintenance records held by the operator, the balloon had been maintained by the pilots at regular intervals, in accordance with the manufacturer s recommendations. There was no record of any outstanding maintenance items. 11

12 1.7. METEOROLOGICAL INFORMATION Balloon flights are normally carried out only if there is no significant weather activity. Flights in the Masai Mara are always conducted early in the morning, normally taking off before sunrise. The pilot had determined that the weather was acceptable for the flight that morning. The weather activity at the time was calm with light winds. Weather did not play a significant role in the accident. The accident occurred early in the morning AIDS TO NAVIGATION None were required and none were available COMMUNICATION Communication was not a factor in this accident AERODROME Balloons flights in Kenya s Masai Mara are launched from launch sites normally shielded from weather. The site used by the operator is about three kilometers from the Mara Sarova lodge within the Masai Mara game reserve. No standard aerodrome or aerodrome equipment was available or required FLIGHT RECORDERS None were required and none were fitted. 12

13 1.12. WRECKAGE AND IMPACT INFORMATION The balloon was completely destroyed by the fire that followed the explosion of the gas cylinder. The accident site was littered with fragments from the cylinder which exploded. The fragments were strewn within a radius of approximately one hundred metres. The envelope, the remains of the basket and the other cylinders were recovered about one kilometer from the original accident site. These had remained attached together almost to the final crash site. All the gas cylinders were found empty, with the relief valves popped MEDICAL AND PATHOLOGICAL INFORMATION The pilot died as a result of the impact from the gas explosion. All the other injuries were as a result of burns from the fire which followed the explosion FIRE There was a fire which destroyed the whole balloon and injured passengers and attendants. The existence of what later turned out to be oxygen, and the liquid petroleum gas -used as fuel- in the rest of the cylinders contributed to the fire build up. The filling of the balloon envelope with hot gases from the fire contributed in the removal of the fire from the original launch site as it floated in air and drifted away in the wind. 13

14 1.15. SURVIVAL ASPECTS The accident was survivable. Normally, initial gas ignition and hot inflation of the balloon are carried out before boarding of passengers. This greatly contributed towards the survival of passengers and other personnel as they were not too close to the initial blast. Availability of transport means from the Masai Mara by way of aircraft which fly in and out of the reserve every day contributed in the evacuation of the injured TEST AND RESEARCH The main components of a hot air balloon are the envelope (on which the registration marks are affixed), basket, burner and the fuel cylinders. The envelope was an A type envelope with a volumetric capacity of 260,000 cubic feet. Liquid petroleum gas is stored in special light weight cylinders for in-flight use. The fuel is stored under sufficient pressure to ensure that it is in liquid form. It is this fuel which is used- through the burner system- to heat the air in the envelope, making the balloon to float. The burner system power output is dependent upon the pressure of fuel in the cylinders. Operating pressure range is psi. The liquid petroleum gas fuel pressurisation is achieved either by cylinder heating or direct supply from a high pressure cylinder. The system used in this case for fuel pressurisation was to be nitrogen gas pressurisation, which is normally done on ground. 14

15 Initial inflation of the envelope is carried out using fans. This is called cold inflation. This is followed by hot ground inflation where the fuel used is from a cylinder outside the basket. Once fully inflated and already floating in air while tethered, the hot ground inflation is disconnected and the inflight cylinders put on line. This is done to improve the payload by taking on board, fuel to be used on the flight only. Passengers are allowed to embark only after the ground hot inflation is concluded. The basket holds the pilot, passengers and the fuel/burner systems. The basket is usually made of woven wicker, with marine grade plywood floor. The wickerwork is woven around stainless steel tubular frames for strength and stability. All loads are carried by stainless steel wires which form a continuous sling around the basket Initial investigation concentrated on the possibility of failure of the cylinder used for ground hot inflation as a result of over-pressurisation or cracks. As the investigation progressed it became apparent that this could not be so. Communication with the cylinder manufacturers however, indicated that the manufacturer was unaware of any instances of cylinder failure due to over-pressurisation during normal operation. 15

16 The working pressure for the gas cylinders is 16 bar, while each cylinder is tested to 32 bar during manufacture. The burst pressure was said to be 64 bar. According to the pressures that companies which fill gas in the cylinders, it was therefore impossible to over-pressurise the cylinders in the absence of fire, by using another cylinder. The pieces of the ground inflation cylinders were studied for pre-accident failure through fatigue stress or cracks. No signs of pre-accident failure were seen. As gas had escaped from all the cylinders during the explosion and the fire that followed, the investigation could not establish the contents of the cylinders destroyed during the accident. The cylinder that had been used for pressurisation of the pre-inflation cylinder was taken to Nairobi and the contents analysed. The cylinder was serial number The cylinder was found to have been filled with pure oxygen, instead of nitrogen gas. The supplier of the gas was requested to present records pertaining to the gas he supplied to the balloon operator. The gas cylinder, from which the ground inflation cylinder had been pressurised, had been supplied to the operator in a batch of six cylinders, serial numbered 40054, 40233, 40277, containing compressed nitrogen, while serial 16

17 number and were 7 cubic meter cylinders containing industrial oxygen. On the delivery note, the cylinder serial number was marked as one of the two containing industrial oxygen. The oxygen was for the operator s use in non-balloon operations. The markings on the cylinder were not very clear, which was considered normal for transit through the rough roads to the Masai Mara game reserve. The operator was found to have no special means to ensure the segregation of the gas meant for balloon operation as opposed to that used for other purposes. This resulted in the mix-up of the nitrogen and oxygen cylinders ADDITIONAL INFORMATION None NEW INVESTIGATION TECHNIQUES None required and none were used. 17

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19 2. ANALYSIS The remains of the failed pre-inflation cylinder were initially studied for pre-ignition failure as a result of pressurisation. On studying the cylinder specifications supplied by the cylinder manufacturer, over-pressurisation of the cylinder during filling was ruled out. Since the cylinder had not exhibited signs of stress or pre-accident failure, analysis ruled out the possibility of over-pressurisation during the gas filling process. The 7 cubic meter cylinder serial number 18458, used to pressurise the failed ground inflation cylinder was taken to the laboratories of BOC in Nairobi and analysed. The contents were found to be pure oxygen. It was therefore apparent that the ground inflation cylinder must have contained a mixture of LPG and oxygen. A mixture of LPG and oxygen would explode immediately there was a source of ignition in the manner that the explosion had occurred. 19

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21 3. CONCLUSION 3.1. FINDINGS The pilot of the balloon was properly trained and qualified. The balloon was properly maintained and was airworthy at the time of the accident. The cylinder serial number 18458, used to fill the ground inflation cylinder, contained industrial oxygen instead of nitrogen. The ground inflation cylinder contained a mixture of liquid petroleum gas and industrial oxygen and a small quantity of nitrogen from previous re-fills. On ignition there was an immediate pressure buildup in the cylinder, resulting in the catastrophic failure of the cylinder. The heat from the fire that followed the explosion of the ground inflation cylinder led to the over-pressurisation of the rest of the cylinders, with a resultant failure of the relief valves, and escape of the liquid petroleum/nitrogen gas mixture. Escaping gases provided more fuel for the fire, leading to the balloon getting airborne and drifting in the wind, away from the launch site. 21

22 3.2. CAUSE The most probable cause of the accident was the explosive ignition of the liquid petroleum/oxygen gas mixture in the ground inflation cylinder. 22

23 4. SAFETY RECOMMENDATIONS 1. Operators should ensure that balloon flight crew can recognise and identify gas cylinders contents through standard colour coding. 2. Crew working on balloon operation should be sensitised to the danger of using the wrong gas to fill balloon gas cylinders. 3. Operators should ensure that required colour coding is visible on all cylinders used in balloon operation. 4. Operators should ensure that gases for use in balloon operation are segregated and stored away from all other gases used by them. Peter M. Wakahia CHIEF INSPECTOR OF ACCIDENTS 23