FLIGHT SAFETY SUB-SECTION
ACCIDENT TO ZS-SAS BOEING 747-244B COMBI -FLIGHT SA 295, 27 NOVEMBER 1987.
REVIEW OF IN-FLIGHT FIRE INVESTIGATIONS SINCE 1987AND THEIR RELEVANCE TO A REVIEW OF THE HELDERBERG ACCIDENT
PART 3: SOMETHING HAD TO CATCH FIRE AND FORM THE INITIAL FUEL
IT WAS MOST LIKELY THE INSULATION BLANKETS MENTIONED IN THE MARGO AND BURGOYNE REPORTS AS HAVING BEEN INVOLVED IN THE FIRE.
The insulation blanket material used aboard ZS-SAS was NOT fireproof!
During the writing of the chapter on the Swissair flight referenced earlier, I discovered many reports of the ignition aspects of the insulation blankets that had, until then, been thought of as fire proof.
Specific to the SA295 matter are AN26 and Mylar blankets.
AN-26 is the brand name for a flammable, polyethyleneteraphthalate (PET) film that covers insulation blankets used in hundreds of Boeing aircraft.
Manufactured by Orcon Corp., it's also known as non-metallised Mylar.
The Federal Aviation Administration says it flew on about 1600 Boeing aircraft including these models:
- 727-200 and 727-200F
- 737-200, 737-200C, 737-300 and 737-400
- 747-100, 747-100B, 747-100B SUD, 747-200B (ZS-SAS Helderberg's model) 747-200C, 747-200F, 747-300, 747-400, 747SR and 747SP
- 757-200 and 757-200PF
- 767-200 and 767-300
Many of these aircraft were also wired with Kapton, including ZS-SAS - it is important to note that this was not fitted to the later designed 777, 787 or 747-8 all designed and built after the mid 1990s.
As detailed previously, in 1993 an MD-87 experienced an in-flight fire while on final approach to Copenhagen.
The aircraft sustained "considerable damage" after an electrical arc had ignited an insulation blanket covered with a metallised version of the PET film (metallised Mylar).
Those blankets had passed the FAA's long-standing flammability test - known as the vertical Bunsen burner test - for insulation materials.
A month after the Swissair tragedy - a full five years after the MD-87 incident - the FAA announced it would be improving the flammability test for insulation blankets within six months and would "require that existing materials be replaced with insulation that can pass the new test." In September 2000 the FAA announced the new flammability standard that it had promised. Why did they do this before the final findings of the investigation were revealed? Because they knew it was flammable. They had known for years.
The rule about this did not become final for another three years --a full decade after the MD-87 incident and nearly 20 after the Helderberg accident.
Boeing however, contended that non-metallised Mylar was safer than the MD series aircraft's metallised Mylar insulation.
In June 2002, Delta Airlines told the FAA's fire safety experts that it had experienced an on-board electrical fire when a shorting wire ignited an AN-26 insulation blanket during maintenance. The minutes of a meeting regarding that incident show that "Delta will replace the AN-26 insulation blankets in approximately 150 of its aircraft during each aircraft's next regular heavy maintenance (HMV) - an aircraft goes through an HMV every 6 years."
On April 1 2005 the FAA finally announced that it was going to propose a rule to completely replace this apparently fire proof material in all airliners that were fitted with it. Read their proposal for rule making here. Of interest in that document is the list of types that would be affected. The Helderberg, had it still been in service, would have fallen under the 747-200 category and it would have had its insulation replaced with a safer material that would not burn.
MY PRIVATE AD-HOC TESTING OF METALLISED MYLAR FILM
I have read that the flammability test used when these materials were authorised for use on the Helderberg was that the insulation blanket be held at 45 Degrees, 30cm above a bunsen burner and that the blanket not be penetrated after 30 seconds. The material must not ignite but if it does it must self-extinguish in less than 5 seconds.
On available documantation on the SA295 aircraft, the insulation blankets in the region above the partition between the Helderberg's passenger and cargo areas, above the life raft support beam (where the Margo report mentions signs of arcing) were between 1 and 8 cm above the Kapton wiring (and may even have been touching it in places) and about 2-4 cm above the 115vAC wiring to the cargo bay lighting units. I therefore decided to conduct an ad-hoc test using a butane flame held near the An26 blankets obtained from an aircraft stripper. The butane flame has a temperature far lower than the temperatures known to exist whenever Kapton wires arc.
Beneath the Mylar I placed layers of cardboard.
WHAT HAPPENED THAT MAY BE RELEVANT TO THE HELDERBERG?
1) The Mylar film caught fire within 3 seconds of being exposed to the heat source.
2) The material burnt with a hissing sound and at a very high temperature while giving off thick smoke and globules of flaming material that fell to the cardboard below.
3) The dropping globules carried on burning on the cardboard.
4) The cardboard sheets caught fire within about 5 seconds after one globule of molten insulation material fell onto them.
4) Much of the dripping molten material burned for some time. Of particular interest is that as it burned on the cardboard, it burned down through successive layers with a smaller and smaller area of burnt material as the depth increased.
Where the globules of molten material continued burning for a lengthy period, very little residue was present after the fire was out..
I do not, in any manner, claim that this test is ground breaking. It merely validates what the Canadian Transportation Safety Board found in investigating Swissair 111 and what the FAA found when using a hot wire - and not a flame - to set fire to AN26 insulation.
Many other journalists have written about this in the past and their investigations support my research.
I do not suggest that my test is 100% scientific nor representative of the exact conditions upon the Helderberg. I do believe however, that the following are valid in this regard:
1. Due to the belief at the time that the insulation blankets and the wiring loom were not fire hazards, their role in the accident that befell SA295 was not investigated.
2. The pattern of damage seen on the stacks of cardboard that showed a small burnt area below, with a widening circle of burnt material as you went higher up the pile would, I suggest, have fooled anyone seeing this without knowledge of the properties of Mylar blankets. The natural assumption when viewing this damage would be that a fire had started in the smaller area below and burnt upwards rather than the other way around.
SO? WHAT NOW? READ PART 4 HOW AND WHY THE SA295 FIRE SHOULD BE RE-INVESTIGATED
Click HERE to watch a supposedly non-flammable An26 and Mylar blanket being tested.
Click HERE to read a report about insulation blankets and their flammable nature.