FLIGHT SAFETY SUB-SECTION
ACCIDENT TO ZS-SAS BOEING 747-244B COMBI -FLIGHT SA 295, 27 NOVEMBER 1987.
A REVIEW OF IN-FLIGHT FIRE INVESTIGATIONS SINCE 1987AND THEIR RELEVANCE TO A REVIEW OF THE HELDERBERG ACCIDENT
PART 4: WHY A NEW INVESTIGATION INTO THE FIRE
During my many years of research into aviation accidents, the one aspect that comes through again and again (with the notable exception of the September 11 2001 crashes) is that the greatest majority of airliner accidents have been just that - accidents occasioned by over confidence, human imperfection, ignorance, assumption and/or a confluence of unplanned and unfortunate circumstances.
Virtually all aviation accidents have fairly logically explained causes. Where some have been initially put down to pilot error or unknown causes, later experience on recurring accidents have led to the revision of the initial findings - such as the Boeing 737 rudder accidents caused by a faulty mechanism.Of interest in those accidents was that the airlines and pilots were initially blamed. The manufacturer pointed the "many other simialr models" that have not crashed so the design "must be safe".
All attempts at getting the investigation into the Helderberg tragedy re-visited have, hitherto, been rebuffed as the authorities have felt - on their version - that the evidence they have been presented by those making the requests is not factual enough to shed new light on the accident.
I doubt very much that the multitude of reports and validated facts about the presence of an ignition source such as Kapton wiring and an initial fuel source in the form of the insulation blankets aboard the Helderberg can be dismissed as insubstantial.
To do so one would have to dismiss the credibility of the respected institutions such as the FAA, the NTSB and its Canadian Equivalent, the AAIB and other similar bodies as well as the many airlines that have wrestled with these materials to highlight, investigate and remove the dangers they posed.
To justify a fresh look at the matter in light of what is now known about the ingition and fire danger posed by these discontinued materials, we have to see if there are any places in the B747-244B Combi cargo area where Kapton and the insulation may have been near to one another and above or near the front right of pallet PR.
This photograph of a B747-200 series Combi Cargo bay reveals that there are at least 10 points where a wiring loom is in direct contact with the insulation material directly above the position of pallet PR. A close look at the image will show that there are other numerous wiring looms in the crown of the fuselage that are also in direct contact or very close to the insulation material.
Image of B747-Combi Cargo Bay PH-BUK on display at an air museum (Courtesy of Walter Van Bel, Belgium.)
THE WHITE OUTLINE: Shows the twin wiring bundles fixed up against the insulation material running the length of the cargo bay. The loom is clamped tightly up against the insulation material at each point where you see a short white clamp. There are at least 10 such clamps above pallet PR, a location where all experts agree, cargo was burnt. Condensed moisture could also have collected at any of these areas and would then have entered any cracks in the wiring loom. Given the knowledge of Kapton wet arc tracking, however, it could have arced and ignited insulation at any point in-between the clamps as well.
THE PINK CIRCLE: This is, as near as is possible to determine and plot on this image, the region of the area of the highest temperatures referenced in the Burgoyne Report.
THE RED OUTLINES MARKED PL AND PR: This gives an idea of where the pallets were. Above pallet PL is the high voltage mechanism for opening and closing the cargo door as well as numerous other wires made of Kapton tied to or clamped against the insulation material.
The partition between the cargo bay and passenger cabin in this aircraft is not as it was in service in the Helderberg. There was a 9G barrier net where the blue curtains are seen in this photo and behind that, a partition with a single width door on the extreme left. As these would interfere with visitor access to the cargo bay more conventional access is in place on the museum aircraft. In other respects the interior of the cargo bay, especially the upper area with control cables, wiring looms, airconditioning ducts and the insulation material is identical to the configuration of ZS-SAS.
CROSS-PLOTTING THE MARGO REPORT WRECKAGE POSITION ON THE AIRCRAFT AGAINST THE BURGOYNE REPORT OF HIGHEST TEMPERATURE AREA BETWEEN BODY STATION 1800 TO 1820 IN THE AREA OF STRINGERS 14-15R PROVIDES THE FOLLOWING RESULT:
THE CORRELATION BETWEEN THE TWO REPORTS STRONGLY SUGGESTS THAT AN UNRECOGNISED FIRE HAZARD WAS NEVER PROPERLY INVESTIGATED
A considered reading of the Margo and Burgoyne reports as well as the inquiry transcript records will show that there are enough references within the record documents to the items now known to be ingredients needed for a fire. It is evident from current knowledge that it was possible for one to have ignited from arcing wiring against the insulation material - especially in the wiring loom above pallet PR. I believe that the the correlation between the reports is too strong to ignore.
This merits, I believe, the CAA of The Republic of South Africa re-visiting the matter along any one (or all) of the following lines of investigation:
If it is, sadly, no longer possible to recover the original wreckage housed on the reconstruction frame in hangar 1 West at Johannesburg International Airport during the original investigation, or to re-examine it. If it was, one could look for evidence of molten insulation blanket material on the floor and on packaging or other cargo material.
With the physical wreckage and other material no longer on hand, then the photographs of same, both in the debris hangar and on the sea bed should be carefully re-examined in light of what is now known about Kapton wire arcing and insulation blanket flammability.
Undertake an investigation using a comprehensive replica of the cargo bay and fuselage just ahead of it. This should use the same type and age of wiring and insulation materials as were present on the Helderberg.
The wiring looms along the right of the cargo bay - and especially where evidence of arcing was found - should be induced to arc to see if this ignites the insulation blankets. Furthermore, the rearwards air flow in the area should be present in order to investigate the development of any fire. The area above the support beam mentioned in the reports could also be a potential source of the fire and thus the materials in that region should be replicated in both their nature and position.
Investigate the effects of the insulation blankets falling in various ways (either totally or in part) or of dropping flaming material onto the cargo to confirm if this could have been ignited and/or in such a manner that the pattern of damage referred to in the Burgoyne and other reports can be re-created.
Re-evaluate the CVR to see if the clicks that were heard were due to electrical pulses caused by arcing wires. These seem to start shortly before the smoke alarm sounded and could very well be the recording of the actual start of the fire. They could laso have been caused by circuit breakers popping and being re-set in the 10-15 minute period leading up to the sounding of the first smoke alarm. This may indicate that an arcing event had occurred in the wiring and the circuit breakers were re-set. If this was done (on the information I have to hand a somewhat routine practice in all airlines) it could have caused a higher temperature event than normal arcing. This could have damaged the metal brackets and stringers as noted in the reports.
These will not be hugely expensive exercises to undertake as the material (either physical or evidential archives) should be at hand.
However, if such investigations are conducted and the premise raised herein is proven inaccurate, the time and energy spent will at least permit a better focus on any further ingnition sources.
On the information now at hand, however, Kapton and the Insulation are the most likely culprits for the tragedy.
PROBLEMS SOLVED BY THIS SCENARIO
The known issues aboard the airliner that the above possibilities address are as foolows:
* The high initial temperature is consistent with the known temperatures occasioned by Kapton arcing - the arcing alone could have cut through stringers and formers of the aircraft.
* The high levels of sooting in the region above pallet PR are explained by the propensity of AN26 blankets to give off large volumes of smoke.
* The damage to the crown section - high above the pallet where the Burgoyne report states only a small fire burned that could not have dmaged items so high up - is explained by the chain-reaciton ignitionof the blankets as the fire travelled upwards.
* The V-Pattern of damage detailed in the Burgoyne report is consistent with flames propagating from the arcing wiring towards the crown of the fuselage.
* The arcing would have caused many circuit breakers to trip.
* The rapid development of the fire is explained (and has been mirrored inother in-flight fires witht hese materials - typically leaving only 5-15 minutes to disaster if the airliner has not landed before that).
* Thie high levels of sooting and the heat damage in the area detailed int he Burgoyne report is acocunted for.
* The high levels of toxic smoke found to have penetrated into the passenger cabin are explained.
* The relatively small areas of fire damge high up ont he pallets of cargo detailed int he Burgoyne and other reports makes sense if they were caused by insulation blankets fallling ont othe palelts while burning.
* The holes burned into the tops of the cargo nets over the pallets are accounted for.
* The inability of the crew to effectively fight the fire is explained.
* The loss of power to the CVR and Data recorders is consistent witht he main wirting loom having undergone severe arcing - it also explains the warbling sound and high-pitched noise recorded ar the end of the recorded data.
* It explains the late onset of the fire after many hours in the cruise - condensation inside the aircraft would have built up sufficiently to pool and run down the formers and collect on the wiring loom.
* It could help to explain the lack of any so-called "death bed" confessions from anyone who may have carried information about sinister causes - it does not discount a sinister cause but the lack of supporting facts for such a cause after so much time is significant.
POSSIBLY THE FIRST KAPTON/AN26 LOSS?
I contend, therefore, that ZS-SAS is, perhaps, the first fatal accident due to the arcing of Kapton wiring igniting insulation materials.
In the case of ZS-SAS, however, fate had conspired to place a pile of combustible materials beneath the burning blankets which, on a normal passenger aircraft, would not have been present. In a similar incident on a full passenger configuration aircraft the risk may well have gone un-noticed save for some burning odour as the insulation smouldered above the service panels and luggage racks that would have limited the amount of oxygen available to sustaint he fire. On ZS-SAS, however, the initial area of ignition was not covered by panelling.
Due to the assumptions made at the time about the non flammable nature of the blankets, however, a frenzied search for a high energy source of ignition within the cargo was launched. The elephant in the room created by the cocktail of Kapton wiring, condensation in the humid interior air near the end of a long flight plus the insulation blanket's propensity to ignite, was, in my view, overlooked.
Considering the record about just how long the information was at hand for the manufacturer and its regulator, however, it is hard not to think that both have conveniently permitted those seeking other sources for the fire to be mis-directed in order to avoid publicity and litigation.
The manufacturer and other authorities that had knowledge of the danger have kept remarkably quiet about these matters. They have, however, replaced both materials in new designs.
Why not remove the wiring from aircraft of that generation still flying then? Simple - they have already removed the insulation and replaced it with non-flammable material. This it is believed, has nullified the proble,. It also of course prevents attornies of those who knwo about the problem from saying - Ha! Got you! You have removed it because you know it is dangerous. THe industry cannot afford to score such an own goal.
It is natural, however, for the US manufacturers and regulators not to wish to have the matter re-visited as they have, so far, not had any burden of responsibility to shoulder. In addition, they will argue, that at the time of the SA295 accident the systems were believed to be safe. They will further point out that action was taken to resolve these issues as soon as the full dangers of the wiring and insulation hazards became apparent.
In any event, retro-active culpability is not and should not be the issue here. The issue is definitive, unsensational resolution of a specific, as yet unexplained airframe loss. The matter goes to the root of the credibility of the Accident Investigation process and profession.
In the circumstances of the day, it is apparent that the investigation into the loss of SA295 was not as thorough, exhaustive or fully scientific as it would be if conducted with current knowledge of these materials and their interaction with one another within the aircraft's fuselage.
The appendices of the Swissair Flight111 report are a treasure trove of data on the number of incidents related to Kapton and insulation fires as well as the dangerous nature of the materials. Simple web searches will reveal most of the intelligence on these two materials.
The FAA and NTSB archives on these issues are another source of information on the matter.
So, a great deal of additional, substantive and factual information is now on hand so that a re-look at the record is well justified.