23:49:00 - Springbok Two Niner Five, eh Mauritius, eh, good morning, eh, go ahead

23:49:07 - Eh, good morning, we have, eh, a smoke, eh, eh, problem and we're doing emergency descent to level one five, eh, one four zero

23:49:18 - Confirm you wish to descend to flight level one four zero

23:49:20 - Ya, we have already commenced, eh, due to a smoke problem in the airplane

23:49:25 - Eh, roger, you are clear to descend immediately to flight level one four zero

23:49:30 - Roger, we will appreciate if you can alert, eh, fire, eh, eh, eh

23:49:40 - Do you wish to, eh, do you request a full emergency?

23:49:48 - Okay Joe, kan jy ... vir ons {Okay Joe can you ... for us}

23:49:51 - Springbok Two Nine Five, Plaisance

23:49:54 - Sorry, go ahead

23:49:56 - Do you, eh, request a full emergency please a full emergency?

23:50:00 - Affirmative, that's Charlie Charlie

23:50:02 - Roger, I declare a full emergency, roger

23:50:04 - Thank you

Map of Flight Progress from Point of Fire Detection to Impact with the Ocean © Gregory Maxwell, 2014

23:50:40 - Springbok Two Nine Five, Plaisance

23:50:44 - Eh, go ahead

23:50:46 - Request your actual position please and your DME distance

23:50:51 - Eh, we haven't got the DME yet

23:50:55 - Eh, roger and your actual position please

23:51:00 - Eh, say again

Two second later at 23:51:02 the Plaisance controller asked the crew for a position report to which the pilot responded that, "Now we have lost a lot of electrics, we haven't got anything on the ... aircraft now."

23:51:12 - Eh, roger, I declare a full emergency immediately

23:51:15 - Affirmative

23:51:18 - Roger

23:52:19 - Eh, Springbok Two Nine Five, do you have an Echo Tango Alfa Plaisance please

23:52:30 - Springbok Two Nine Five, Plaisance

23:52:32 - Ya, Plaisance

Further communication with the crew occurred at 23:52:33 with the controller requesting an ETA at Plaisance, the crew estimated a 00:30 arrival.  At 23:52:50 the controller overhead an inadvertent transmission from the pilot, "Hey Joe, shut down the oxygen left."  After this transmission their was 8 minutes and 44 seconds of silence until the next transmission. 

00:01:34 - Eh Plaisance, Springbok Two Nine Five, we've opened the door(s) to see if we (can?) ...we should be okay  

Then at 00:01:36 the pilot again is overheard giving instructions to the flight engineer, but most of the conversation was unintelligible.

00:01:45 - Donner se deur t... (Close the bloody door) (?)

00:01:57 - Joe, switch up quickly, then close the hole on your side

00:02:10 - Pressure (?) twelve...thousand

00:02:14 - ... ...Genoeg is ...Anderster kan ons vlug verongeluk (is enough...Otherwise our flight could come to grief)

00:02:25 - Carrier way only

00:02:38 - Eh Plaisance, Springbok Two Nine Five, do (did) you copy

00:02:41 - Eh negative, Two Nine Five, say again please, say again

At 00:02:43 the pilot reported that he was 65 nautical miles out, this report was misunderstood by the Plaisance controller to be distance from the airport instead of the next waypoint Xagal.  At that moment in actuality SAA295 was about 145 nautical miles from the safety of Plaisance Airport.  

00:02:45 - Confirm sixty fie miles

00:02:47  - Ya, affirmative Charlie Charlie

00:02:50 - Eh, roger, Springbok eh Two Nine Five, eh re you're recleared flight level five zero.  Recleared flight level five zero.

00:02:58 - Roger, five zero

00:03:00 - And, Springbok Two Nine Five copy actual weather Plaisance Copy actual weather Plaisance. The wind one one zero degrees zero five knots.  The visibility above one zero kilometers, and we have a precipitation in sight to the north.  Clouds, five octas on six zero zero, one octa five thousand feet. Temperature is twenty two, two two.  And the QNH one zero one eight hectopascals, one zero one eight over.

00:03:28 - Roger, one zero one eight

00:03:31 - Affirmative, eh and both runways available if you wish

00:03:43 - And two nine five, I request pilots intentions

00:03:46 - Eh we'd like to track in eh, on eh one three

00:03:51 - Confirm runway one four

00:03:54 - Charlie Charlie

00:03:56 - Affirmative and you're cleared, eh direct to Foxtrot Foxtrot.  You report approaching five zero

00:04:02 - Kay

There were no further transmissions from the aircraft and the approach controller at Plaisance tried unsuccessfully for the next 30 minutes to re-establish communication with the aircraft but there was only silence in response.  The aircraft crashed into the Indian Ocean at approximately 00:07:00, the time being established by examining two damaged wrist watches recovered from pieces of carry-on baggage.

Search and Rescue Efforts

Mauritius search and rescue officials began a search for the aircraft the next day, scanning the ocean for any signs of survivors but it became quickly apparent that the crash was not survivable.  The pattern and type of debris that was found floating on the surface suggested that some catastrophic failure had overtaken the 747.

On November 30th the decision was made to end the search for survivors and focus on the recovery of bodies and aircraft wreckage.  The search was initially focused on the floating debris field which was slowly drifting in a westerly direction.  Helicopters were used to search coral reefs for wreckage that may have become entangled while surface ships recovered floating wreckage.  The surface debris search was suspended after 8 days on December 10th.

Floating debris recovered from the ocean consisted mainly of light cargo, cabin paneling, cabin furnishings, escape slides and rafts in addition to some pieces of carry on luggage.  Secondary parts of the wings were also recovered, such as access panels and pieces of the wing leading and trailing edge.

Map Showing Distance from Mauritius and the Aircraft's Last Known Position Fix © Gregory Maxwell, 2014

Undersea Search

On December 11th the investigators began their search for the CVR (Cockpit Voice Recorder) and FDR (Flight Data Recorder) by utilizing sonar to listen for the underwater pingers attached to the recorders.  The pingers were designed to transmit for a period of 30 days, until such time as the battery supply was exhausted.  A search grid was established based on the aircraft's last known position and the time of impact as established by the wrist watches recovered from carry-on luggage and the rate of drift of the surface debris.   

A vessel from Mauritius was contracted to perform the sonar survey of the ocean bottom.  The survey which lasted from the 12th through the 21st of December revealed some small pieces of debris, which were confirmed to have originated from ZS-SAS after visual examination of the underwater video footage.  The sonar survey was ultimately unsuccessful in locating the aircraft's flight data and cockpit voice recorders.  A second search was commenced using a ship equipped with side scan sonar equipment, and after just three days the main wreckage area was found and marked by underwater sonar beacons resting at a depth of 14,436 feet.

The wreckage of the Helderberg was strung out on the sea floor in two oblong debris fields with the aircraft split into two main sections.  The fact that the aircraft's front and rear section were found in two separate debris areas suggests that it broke up in flight, prior to the impact with the sea surface.  The aircraft debris field on the sea floor was aligned with 320 degrees magnetic, which approximates the direction of the ocean current in the area at the time.  The two main wreckage fields were referred to by investigators as the northeastern and southwestern areas

The northeastern debris field was approximately 2,953 feet long by 1,476 feet wide, and the centers of the two wreckage fields were located 1,968 feet apart.   In between the two main wreckage areas some small pieces of debris and cargo including computers were found strewn about.

The northeast debris field contained 70% of the aft fuselage structure rear of door number four, and included major structural pieces such as the main deck cargo door, horizontal and vertical stabilizers, two sections of the main deck cargo floor, the rear pressure bulkhead, the auxiliary power unit, tail cone and large concentrations of freight contained in the main deck cargo area.

Photo of Wreckage on the Bottom of the Indian Ocean, Fuselage Section is Same Depicted in Graphic Above

The southwestern debris field contained the fuselage structure forward of door number four but unlike the rear section the forward section was highly fragmented.  Major structural items found in this area included three of the four engines, all five landing gear assemblies and major pieces of both wings.

Salvage Operation

Due to the depth of the wreckage and given the technology available at the time of the accident, recovery of the debris was a massive challenge.  Investigators were forced to prioritize recovery efforts to focus on retrieval of key pieces of debris as it was cost prohibitive and unfeasible to attempt to recover every piece of the aircraft debris.  The highest priority was obviously locating and retrieving the the FDR and CVR recorders.  Without this data it would be difficult to discern exactly what the crew were experiencing and how the aircraft was being effected by the fire in the main deck cargo compartment.

With the aid of an ROV with camera equipment the team of salvagers directed by the the investigative team from the South African Civil Aviation Authority photographed 3,940 areas of interest and recorded 806 hours of video of the debris field and main wreckage.

The primary focus of interest for investigators was the main deck cargo compartment where the fire had originated.  The team attempted to recover as much debris from this section of the aircraft as well as the surrounding areas that showed direct heat damage.  They were aided in their efforts to identify pieces of interest by representatives from both South African Airways and Boeing.  However the team's salvage attempts were hampered by the ROV's limitations and ultimately only 25 targets of significance were able to be recovered from the sea bed.  Among the items recovered were the CVR, rearmost galley support structure, sections of the main cargo deck, fuselage skin from the crown of the aircraft and a section of the rear pressure bulkhead.

Examination of Floating Debris

None of the wing components, items from the forward upper deck or from the passenger cabin exhibited any signs of heat damage or soot from smoke exposure.  A portable fire extinguisher recovered from door 2R showed sooting and had a splatter of molten plastic on the bottle.  Investigators also noted that the galley stowage doors and lower portions of cabin door 4R had soot deposits on them.

To the team's surprise, all checked baggage and cargo found and identified as coming from the lower deck cargo hold, beneath the main deck cargo compartment, showed no signs of either heat damage or soot that would suggest exposure to fire. 

However cargo that was identified as having come from the main deck cargo area was heavily scorched and burned, while cosmetic paneling from the passenger cabin adjoining the main deck cargo area had heavy deposits of soot.  In addition the bulkhead door separating the cargo and passenger compartments was distorted due to heat damage and had become delaminated.  The door frame and hinge showed signs of smoke streaking and distortion from heat exposure.  The team also identified heat damage on the number 5 left and right doors, a shelf from the aft coat closet and a section of the left upper side wall lining.

Examination of the Wreckage Recovered from Sea Bed

Smoke and heat damage were identified on fuselage structures recovered and positively identified as being located above the passenger cabin ceiling, as well as areas above the rear galley on a load bearing beam at the back of the passenger cabin.  This beam contained deposits of melted aluminum and nylon material. insulation of wiring in the immediate area was burned away and the wires showed signs of arcing.  These wires were identified as being the AC power leads for the main deck cargo compartment crown lights.

Pieces of the forward left main deck cargo floor were also recovered and contained deposits of both melted aluminum and nylon on the upper surface, but there was no evidence of heat or smoke damage on the underside of the floor panel.  Portions of the outer fuselage sections from the side and crown of the aircraft exhibited signs of heat distortion and paint bubbling.

Main Deck Cargo Compartment Showing Location of Pallets and Position of Key Pieces of Debris Recovered

Lower portions of two of the straps from the 9g cargo barrier net forward of the PR pallet position were damaged by heat exposure below the cabin window level, above that level the straps had been burned away completely.

Heavy sooting and evidence of heat exposure were present on the left and right top panels and upper surfaces of the rear galley unit.  Portions of the outer fuselage skin on the right side of the aircraft adjacent to pallet position PR showed blistering and discoloration of the paint as well as deformation and buckling of the skin.

Sections of the upper half of the aft pressure bulkhead contained heavy smoke deposits and heat discoloration.  The elevator cables were still attached and the control cable aperture seals were damaged. Investigators also discovered light traces of smoke deposits on the back surface of the bulkhead.

Wreckage Observed but Not Recovered from Sea Bed

The team through video footage analyzed major components of the left wing and body gears, the right wing gear and the nose gear and determined the landing gear was retracted at the moment of impact with the sea.

Three of the four jet engines were located and visual analysis showed that all three had experienced severe impact damage.  The distortion of the fan blades suggested that the engines were operating at a low power setting and producing minimal thrust at the moment of impact.

A large section of the fuselage which included most of the main deck cargo door frame was found to have severe heat damage in the crown skin and heavy smoke deposits all the way down to the door frame at the base of the cabin floor.  Pieces of the cargo compartment floor still attached to this segment contained deposits of molten material between the 9g barrier and pallet position PL.  Unlike the the right side, portions of the straps securing the retaining barrier on the left side were still largely intact all be it with noticeable heat damage.

Reconstruction of the Fuselage Section Containing the Main Deck Cargo Door Frame as Shown in Graphic Above

The horizontal stabilizers was found completely intact with elevators still attached.  However the leading edge of the left stabilizer was detached and was bent upwards.  The right stabilizer inboard root rib of the leading edge was deformed which indicated to investigators that the aft fuselage structure had twisted in a counter-clockwise direction.

The vertical stabilizer was found largely intact with portions of the fuselage structure still attached.  Both the upper and lower rudders were still attached to their mountings and there appeared to be no evidence of smoke exposure or heat distortion.

Cargo Manifest

14,588 kg (32,161 lbs) of cargo was loaded into the main deck cargo compartment on six pallets.  The cargo consisted of a mixture of electronic components (computers) and parts, hardware, paper articles, textiles, medicines and sports equipment.  The aircraft was also rumored to have been transporting an undetermined quantity of fire works however after extensive investigation into this theory the team were not able to substantiate this claim.  Tests for traces of nitrates and ferrites on the pieces of cargo and airplane wreckage recovered proved inconclusive.  However even a very small amount of fireworks as noted by the team could have provided a source of ignition because of the inherent instability of the chemical makeup of most pyrotechnic devices.

Most of the cargo was packed using highly flammable polystyrene, polyurethane or polyethelene products, while lighter articles were packed in cardboard cartons.  Heavier items like machine parts were either contained in wood crates or small wooden boxes.  The pallets were noted to have been stacked on average about 2 meters (6.5 feet) high.

CVR Analysis

The salvage operation was able to successfully locate and retrieve the CVR. Unfortunately the DFDR (Digital Flight Data Recorder) which was positioned immediately adjacent to the CVR on the left aft side of the main deck cargo compartment was never located, nor was the QAR (Quick Access Recorder) which was positioned in the main equipment bay forward of the lower cargo hold.

The body of the recorder was damaged from the impact and the paint was blistered from exposure to heat. Electrical wiring insulation was scorched and the solder of some of the wiring joints had melted.  This indicated to the investigators that the unit was exposed to temperatures of at least 183 C (361 F). Examination of the interior of the unit unveiled oily soot deposits that they believed penetrated through an aperture in the front cover.  The heat and resulting damage to the solder joints on the device and the electrical wires running from the CVR through the overhead ceiling of the main deck cargo compartment had caused the device to short circuit and stop functioning.

The CVR was designed to record all verbal communication from flight deck crew members through mics in the oxygen masks, hand held and overhead microphones in the audio selector panels of the captain, first officer and flight engineers stations.  Unfortunately the device was not set up as a hot mic to recorded everything within range of the microphones on the flight deck.  Instead it only recorded when the mics picked up speech between crew members through any of the previously mentioned input devices.  For investigators this meant that vital sounds, instrument indications and warnings possibly were not captured on the CVR tape.

Another problem for investigators is they were not able to sink the CVR recording with the recordings from Mauritius ATC as the CVR record didn't contain either the last HF communication with Mauritius at 23:14:00 nor the the first VHF communication with Mauritius approach control at 23:48:51.  A further issue was discovered when the tapes were played back as only the last 1 minute and 14 seconds of the 29 minute 52 second recording were able to be clearly deciphered.  Despite this the team was reasonable confident that conversations up to the point the fire alarm bell rang were of a personal nature and inconsequential to the accident.  Below are the last 1 minute 14 seconds of the CVR recording.

28:31 - Fire alarm bell (was stopped very quickly by the crew)

28:35 - Intercom chime

28:36 - What's going on now?

28:37 - Huh?

28:40 - Cargo?

28:42 - It came on afterwards

28:45 - Strong click sound hear and simultaneously And where is that?

28:46 - Click sound again

28:48 - Just to the right

28:49 - Say again(?)

28:52 - Main deck cargo

28:57 - Then the other one came on as well, I've got two

29:01 - Shall I (get/push) the (bottle/button) over there

29:02 - Ja (Yes)

29:05 - Lees vir ons die check list daar hoor (Read the check list there for us please) followed by a double click sound

29:08 - The breaker (presumably referring to the circuit breaker) fell out as well

29:09 - Huh (Two click sounds)

29:11 - We'll check the breaker panel as well

29:12 - Ja (Yes)

29:33 - Fok dis die felt dat altwee aangekom het - dit steur mens (Fuck it is the fact that both came on - it disturbs one)

29:36 - Intercom chime (while captain is speaking)

29:38 - Aag shit

29:40 !!! (800 Hz test tone signal commences)

29:41 - Wat die donner gaan nou aan? (What the hell is going on now?)  This is said in a surprised tone of voice.

29:44 - Sudden loud sond

29:46 - Large and rapid changes in amplitude of test tone start

29:51 - End of test signal, very irregular near end

29:52 - End of recording.  There is about 1 second of old recording on this side of the tape.

The test tone which occurs simultaneously on all four CVR channels is and indication that both the audio input and test signal wiring were being affected by exposure to the fire.

Examination of Human Remains

Remains from 8 separate individuals were identified and five were tied to a specific individual and their seat location in the aircraft determined.  Six of the eight persons had extensive injuries to the upper parts of their body including the head, chest and ribs. 

Soot was found in the lower respiratory tract of all eight vicitims.  All the individual remains were tested for the presence of carboxyhaemoglobin.  The results showed saturation levels as high as 60.9% and 67.2%. The tests did not reveal the presence of cyanide in the bloodstream of any of the victims.  The seat assignments of the two individuals with the highest saturation levels were identified as 30E and 40D.  The remaining three people were assigned seats 37A, 37D and 42A.

Origin and Propagation of the Fire

The flight crew were first alerted to the presence of a fire in the main deck cargo compartment when a smoke detector alarm signal was triggered on the flight engineer's panel, 28 minutes and 31 seconds into the CVR recording.  About 26 seconds later a second smoke alarm signal also from the main cargo deck alarmed, as noted in the CVR recording with the flight engineer stating "Other one came on as well, I've got two".  At 29 minutes and 5 seconds on the CVR the captain can be heard asking for the main deck cargo fire checklist to be read.  Less than a minute later at 29 minutes 52 seconds the recording ends, this event occurs 1 minute and 21 seconds after the first fire alarm bell was heard on the flight deck, suggesting the spread of the fire was rapid and quickly compromised the electrical system wiring in the crown of the fuselage which included the wiring between the CVR and the flight deck.  

The main deck cargo compartment in the 747-200B Combi is a Class B compartment and is divided into two smoke detection zones, each of which is equipped with dual smoke detection system that is tied to an alerting system on the flight engineers panel on the flight deck.

Origin of the Fire at Pallet Position PR in the Main Deck Cargo Compartment © Gregory Maxwell, 2014

Investigators determined through examination of the wreckage and confirmed by the alarms received from the main deck cargo compartment on the CVR that this was the origin of the fire.  Structures in this section of the airplane had the most damage from both smoke and heat exposure.  With the origin of the fire and area with the highest heat intensity being pallet PR.  However despite recovering almost all of the contents of this pallet the team was unable to determine the source of ignition.  

Cargo retrieved from the sea surface and observed during the underwater wreckage survey that was identified as coming from pallets PR, RR and SR showed varying signs of heat damage, while no cargo from pallets PL, RL or SL found showed any signs of heat damage.  South African Airways was not aware of any hazardous materials being transported according to the waybills of the shipments loaded onto the aircraft. Further the cargo manager for SAA at Taipei stated that he had not been informed of any dangerous cargo that made up the load for SA295.  

Six consignments of electronic equipment were discovered to contain small lithium battery cells which were fitted to the circuit boards, but these cells were considered non-dangerous.

A representative from Taiwan's Commissioner for Customs informed investigators that a random sampling of the cargo on the flight had been undertaken with a computer selecting 10 house waybills and one master waybill.  The inspection revealed that all 11 consignments matched the waybill documentation provided.

The team also followed up on a theory that the South African Defense Force was using the flight to transport weapons or explosive devices, but the Chief of the SADF confirmed to investigators that no such materials were being transported on SA295.  This would be a direct violation of ICAO and UN statutes which expressly prohibit the transport of military hardware and munitions on passenger transport aircraft.

Boeing Emergency Procedures for Main Deck Cargo Fire

The emergency procedures for dealing with a fire in the main deck cargo compartment were part of the Emergency Operations Checklist carried on the flight deck.  The procedures require that the crew don their oxygen masks and if required smoke goggles.  One of the flight attendants at the Captain's request must also don an oxygen mask and portable oxygen cylinder and if directed enter the cargo compartment via the bulkhead door.  After closing the door the attendant in order to gain access to the cargo area and fight the fire must first retrieve the fire extinguisher from its storage area, unclip the cargo barrier to gain access to the pallets and locate and attach the 3 meter long extinguisher nozzle extension.  The attendant must then locate the source of the fire and apply the extinguishing agent. Meanwhile the captain must locate the nearest suitable airfield and land immediately.

In the event that smoke enteres the passenger cabin the flight crew is instructed to follow and execute the Upper and or Main Deck Smoke Evacuation check list depending on the location of the smoke condition. The procedure calls for the non flying pilot to identify the passenger compartments affected by smoke and for the flying pilot to execute and emergency descent to 14,000 feet if and when the smoke condition is identified as severe and an immediate landing is not possible.  

In this situation the flight deck personnel must go on 100% oxygen.  The non-flying pilot must then identify which cabin doors to open to evacuate the smoke.  Before conducting this procedure the aircraft must be depressurized and slowed down to a speed of less than 200 knots.  The flight attendant must then place the involved door in manual mode.  Only at the captain's direction should the doors be opened to evacuate the smoke.

Evidence of Crew's Attempt to Fight Fire

Investigators noted that two of the cargo barrier net clips had been released at their retainer fittings which indicated that someone had entered the cargo compartment from the passenger cabin.  Additional evidence of the crews attempts to fight the fire were seen on the fire extinguisher later identified to have come from door 2R.  The extinguisher from door 2R was recovered on the sea surface and was noted to be full but had deposits of molten cargo barrier material on its housing.  This extinguisher was the only one of the aircraft's 11 total fire extinguishers recovered.  The crew had at its disposal eight 2.5 lb Halon fire extinguishers and three 3.63 lb water extinguishers with which to combat a fire.

Search for an Ignition Source

In an effort to determine the ignition source of the fire investigators interviewed and made site visits to multiple shippers who's products made up the cargo manifest of SA295.  The team was particularly interested in testing the lithium battery cells installed in many of the computers and electronic equipment, as they had uncovered reports of certain types of lithium batteries exploding in emergency locator beacons.

Six small battery cells, similar to those installed on the electronic equipment shipped as cargo on SA295 was examined.  Two of the battery cells were identified as being composed of a lithium-thionyl chloride, two were lithium-carbon monoflouride and the remaining two were nickel-cadmium.  The tests concluded that the small size of the battery units, most were the size of a small coin, and their low capacity (less than 1900 mA/hr, made them unlikely sources of ignition.  The nickel-cadmium batteries, which were in various states of charge on SA295 were generally accepted as being very safe to transport.  The report further noted that lithium-thionyl chloride cells are generally safe to transport as long as they are stored properly and not subject to excessive heat or physical abuse which could cause them to short circuit and auto-ignite.

Fire's Effect on Fuselage Structure

Investigators were also interested to know how the fire, as it grew in intensity and spread through the cargo compartment affected critical aircraft systems and the airworthiness of the aircraft.  The focus of the analysis was the crown of the fuselage structure above the main cargo compartment where the fire was most intense and damage to aircraft systems occurred.  Under normal operating conditions at cruise altitude the maximum operating maneuvering loads are 1g plus or minus 0.3g assuming a cabin pressure of 8.9 psi.  It is possible that the aircraft loading exceeded 2g's during its emergency descent from FL 350 to FL 140.  The team calculated that the descent took 3 minutes and 30 seconds and the aircraft's nose down pitch angle varied from a high of 15 degrees at the start of the descent to around 10 degrees during the stabilized descent. Investigators considered the possibility that the fuselage crown structure weakened by exposure to the fire was further compromised by the loads placed on it during the emergency descent.

Fire's Effect on Electrically Driven Systems

Electrical wiring and control cables routed through the main cargo deck crown were separated into two corridors or raceways on the left and right crown of the fuselage crown.  These wiring bundles fed various systems in the tail of the airplane including the CVR, DFDR, autopilot systems, yaw damper controls, stabilizer trim controls and cabin interphone system among others.  From the CVR investigators were aware that these systems were being progressively compromised by exposure to fire, as the distinctive popping sound of the circuit breakers could be heard on the flight deck panel through out the recording.  The flight crew also made several comments about the breakers popping.  The fire caused the system wiring to short-circuit resulting in the tripping of the circuit breaker to isolate power to the affected system and triggered a cascade of warning lights and alarms to alert on the flight deck.  In total the team believed that at least 80 individual circuit breakers were tripped.

Fire's Effect on Flight Control Systems

Even with the loss of these electrically powered systems some of which control critical control functions in the elevators and trim controls on the horizontal stabilizer the pilots would still have retained adequate control over the aircraft. Boeing had considered loss of these systems during the design of the aircraft.  Ensuring through rigorous design reviews and testing that loss of these systems would not adversely inhibit the controlability of the aircraft.

For example the horizontal stabilizer trim which was normally electrically controlled and hydraulically operated, could be controlled manually in the event that the electrical system that powered it failed.  The elevator and rudders on the 747 were cable controlled and hydraulically boosted and not dependent on electrics for actuation.  Conversely loss of the yaw damper control was not a critical failure as the system was designed primarily to reduce fatigue loads on the structure during encounters with turbulence.  All of these systems and control units were designed to maximize the handling qualities of the aircraft and provide the most comfortable ride for passengers, not to serve as structural load limiting protections during manual flight modes by the pilot.  In other words the aircraft could still fly safely with the loss of any or all of these control inhibiting systems.

Fire's Effect on Flight Deck Systems

Critical electrically driven flight deck systems were also backed up by standby battery power in case of an electrical failure.  The fact that the pilot was still able to communicate with Mauritius control via VHF radio even after remarking that he had lost all his electrics is a sign that the standby 28v DC bus was still powered. Batteries also supplied emergency power to the No. 1 ILS and marker beacon, secondary artificial horizon instrument, No. 1 Glide Slope receiver, No. 1 HSI, No. 1 ADI, No. 1 INS, main interphone system and the cabin P.A. system.

Design of the Boeing 747 Combi

The aircraft was certified with the idea that in the event of a cargo fire the smoke detection system would quickly alert crews to the threat in sufficient time to locate the source of the fire and extinguish it before it had a chance to take hold and spread out of control.  

The basic design of the 9,600 cubic foot compartment it was thought would help ensure that byproducts from the fire like smoke and flames would not penetrate the passenger cabin due to a built in pressure differential between the two compartments.  A 25 cm (.8 in) thick partition fitted just forward of the cargo door separated the passenger cabin from the cargo space.  This partition was not designed to provide an air tight seal but rather to restrict airflow between the two zones.  By controlling the direction of the airflow within the aircraft and air circulation patterns the air pressure in the cargo compartment could be kept at a slightly lower pressure than the passenger cabin which would inhibit transmission of smoke into the cabin in the event of a fire in the cargo compartment.

However this design concept failed to take into account thermal expansion caused by a fire in a real world scenario.  During certification Boeing was required to test the effects of thermal expansion on the 747 combi but the smoke generated from combustion of bundles of tobacco leaves only produced a thermal release of 6,000 BTU's, far below the thermal release experienced during the fire aboard ZS-SAS.  

Following the accident the FAA used a computational model to try to determine whether thermal expansion could have caused flames and smoke to enter the passenger cabin of the aircraft.  For their calculations they used a fire that produced a constant 10,000 BTU's per minute, and the results showed that this rate of thermal expansion would very quickly eliminate the small existing pressure differential between the cargo compartment and the passenger cabin.  The FAA chose the 10,00 BTU figure based on the fact that polystyrene and polyurethane, the most common packing materials used on the cargo on SA295, had thermal expansion rates of 18,100 and 10,300 BTU/lb respectively.  The FAA's calculations seem to be supported by the medical examiner's findings of soot in the respiratory tracts of the human remains recovered, in addition to the heat damage and sooting found in the rear galley.

FAA Review of Certification of Class B Cargo Compartments

In response to the accident the FAA appointed a team to review standards associated with the certification of main deck class B cargo compartments on Combi aircraft like the Helderberg.  After much study and review of the accident record and known facts about the case and other incidents the board concluded the following:

1.  The existing rules, policies and procedures being applied to the certification of class B cargo or baggage compartments in terms of smoke and fire protection are inadequate.

2.  The use of pallets to carry cargo in class B compartments is no longer acceptable.

3.  While entry into the cargo compartment is available, not all cargo is accessible.

4.  It is unlikely that personnel would have the means available to extinguish a fire (particularly a deep-seated fire).

5.  The reliance on crew members to fight a cargo fire must be discontinued.

6.  The quantity of fire extinguishing agent and the number of portable extinguishers are inadequate.

7.  The level of visibility in a smoke filled cargo compartment is not adequate for locating and fighting a fire with a portable fire extinguisher.

8.  Most existing transport airplane smoke or fire detection systems were certified prior to FAR 25 Amendment 25-54 and are incapable of giving timely warning.

9.  There were differences in the smoke testing procedures and criteria used from manufacturer to manufacturer, prior to issuance of FAA Advisory Circular (AC) 25-9.

Inadequate Fire Protection for Class B Main Deck Cargo Compartments

The lower deck cargo holds were both fitted with photo-electric smoke detectors in each of the compartments.  When a smoke alarm was triggers it would result in a warning light being displayed on the flight engineers panel, indicating which compartment sensor had been triggered.  The flight engineer could then by a press of a button automatically discharge the two freon gas fire extinguishers into either the forward or rear cargo compartment.  The same was true of the APU compartment which had a separate semi-automatic fire extinguishing system that could be triggered from the flight deck.

By contrast to combat a fire in the much larger main deck cargo compartment there were no automatic fire suppression systems installed on the 747-200B Combi.  Instead one or more crew members were relied upon to enter the dark cargo compartment, where visibility was most likely limited by smoke and quickly locate the source of the fire and extinguish it.  While in practice this sounded like a feasible solution, the FAA and Boeing never considered the type of fire that occurred on SA295.

Both the intensity of the fire and the temperature made it almost impossible for the crew to effectively fight the fire with hand held extinguishers.  By the time the crew were alerted to the presence of the fire in the cargo compartment it was most likely too late to contain it by the means available.  However even if the crew had been aware of the fire earlier it is difficult to say whether they would have been able to extinguish it, especially if the fire was seated deep within the middle of the pallet near the bottom of the stack as was theorized.

The ability of crew members to reach the fire was also inhibited by the limited space in the compartment. There was not a lot of room between the pallets and side walls for the crew to maneuver around to get in position to fight the fire.  It would have taken both hands to hold the 16 lb extinguisher and the 10 foot long extension wand.  The crew's efforts to extinguish the fire would have had the highest probability of success if the origin of the fire was on the outside of the pallet stack and easily accessible to them from a safe distance. 

The fire that took hold in the PR pallet was very hot and any person in close proximity to it would have been quickly overwhelmed by the radiant heat and been forced to retreat back into the passenger cabin after only a short time.  It is likely that any attempts to fight the fire were quickly abandoned as the fire grew in intensity and the temperature in the compartment began to elevate.

As a result of their findings the investigators recommended that no new main deck class B compartment designs be approved to existing class B criteria and that main deck cargo compartments provide a level of safety equal to class C compartments or that cargo be carried in fire resistant containers meeting class C requirements, including smoke detection and automatic fire suppression capability.

Use of the Smoke Evacuation Checklist

When the crew began the emergency descent in preparation to evacuate the smoke from the passenger cabin they would have referenced and completed the Smoke Evacuation Checklist.  Part of this checklist requires that the cabin recirculating fans be turned on again.  These fans had been previously shut off as part of the Main Deck Cargo Fire/Smoke Checklist to help prevent smoke from entering the passenger cabin through the air circulation system and help isolate the cargo compartment air supply.  Unfortunately for the crew of SA295 the Emergency Checklist did not spell out clearly that the smoke evacuation checklist was only to be used if and when the fire in the main deck cargo hold had been extinguished.  But with the smoke situation growing worse in the cabin the crew followed the procedure as dictated in the manual to get rid of the smoke.

The flight crew did not realize by turning on the recirculating fans they actually made the problem much worse as now the smoke and byproducts of the raging fire in the cargo compartment were carried by the ventilation system into the passenger cabin.  This accelerated the spread of the fire, giving it a pathway through the partition and increasing the rate at which toxic smoke and gases were entering the passenger cabin. Investigators believe it is possible that the recirculating fans continued to operate through the rest of the flight absent a loss of electrical power.

Conclusions of the Investigators

What is known is that a fire ignited in the PR pallet, the fire developed rapidly and could not be controlled by crew members.  The fire generated smoke, carbon monoxide and carbon dioxide, some of which penetrated the passenger cabin and possibly the flight deck.  However the complexities of how air flows inside an aircraft cabin when driven by a thermal driver such as a fire, and unknowns such as the rate of penetration into the cabin and the duration the recirculating fans ran makes any definitive conclusion impossible to reach.

The ignition source of the fire was never determined, but an explosion was ruled out based on detailed examination of the aircraft wreckage and the absence of a rapid depressurization of the aircraft, which would have almost certainly followed the detonation of a device in the main deck cargo compartment.  No such event is noted by the crew on the CVR recording.

Nothing listed on the cargo manifest, or waybills on pallet PR could be described as dangerous goods.  Nor had the team recovered any item of cargo from this pallet that seemed suspicious.  But the possibility remained that a mis-declaration or deliberate false declaration on the waybill could have concealed a dangerous shipment from the cargo manager and customs officials in Taiwan.

Whatever the source of the fire was, the packing material and cardboard boxes would have provided sufficient fuel to the fire, in the process allowing it to reach the high temperatures evidenced on the wreckage and potentially caused a flash fire in a matter of minutes.  Investigators believe if a flash fire had occurred in the crown of the main cabin cargo compartment that the temperatures could have reached 2,000 F and the condition could have been sustained from anywhere between 30 seconds and 2 minutes.

The burning of the packing materials produced the smoke, carbon monoxide and carbon dioxide which penetrated the cabin and may have asphyxiated the passengers and possibly even the flight deck crew before the aircraft crashed.

Possible Causes of the Crash

The crew may have been overtaken by the toxic levels of carbon dioxide and carbon monoxide in the air and lost consciousness which resulted in the aircraft crashing.  It is also possible that the levels of smoke in the flight deck and loss of instrumentation lead to disorientation of the flight crew which led to the crash.

The aircraft structure, weakened by exposure to fire may not have been able to withstand the aerodynamic loads imposed on it which led to an in flight break up.  This theory is supported by the two distinct and separate debris fields found on the sea bottom.  Experts from engine maker Pratt & Whitney in their analysis concluded that the engines were rotating at a very slow speed at impact which indicated to them that the airplane was no longer flying but falling or tumbling.

The investigators also considered that the flight control cables were compromised by the fire to the point of failure causing the flight crew to loose positive control of the aircraft's elevators which made the aircraft uncontrollable.

What can be stated with certainty is that the effects from the fire directly led to the aircraft crashing into the sea.  But beyond that conclusion the investigators were not able to precisely identify the chain of events that led to the loss of the aircraft.

Final Thoughts

We will probably never know what happened to the passengers and crew of the Helderberg on that dark night in 1987 over the Indian Ocean.  Although the cause of the crash was never definitely determined the accident and the subsequent investigation did go a long way towards advancing the cause of safety for the flying public.  The regulations pertaining to certification of Combi aircraft and class B main deck cargo compartments were significantly modified and much stricter standards were enacted.  These stricter standards including automatic fire suppression systems were incorporated into the design of the 747-400 Combi model, which continues to operate in mainline service for several airlines to this day.