Accident to a Boeing 737 Aircraft. In 1979, a Boeing 737
aircraft on a scheduled flight from Trivandrum to Madras suffered a mid-air explosion about 20 minutes before landing, causing in- juries to the crew and damage to the cockpit instruments and the front toilet area. In spite of multiple emergencies, the pilot contin- ued to fly and made an emergency landing at Madras. The aircraft overshot the runway, the engines got severed, and the undercar- riage and underside were damaged. Although it was known that a mid-air explosion had occurred, it was necessary to provide ma- terial evidence to the Court of Inquiry to establish the cause.
Detailed examination of the wreckage including the nature and extent of damage to the aircraft clearly pointed to the front toilet area as the possible center of explosion. References 5, 6, and 10 provide details of this investigation. A large number of tiny metal fragments were recovered from the front toilet compartment, the cockpit, and the ground below and were studied in detail by optical and scanning electron fractography.
The waste towel receptacle, which is usually kept below the wash basin in the toilet, had disintegrated into fragments that were found to have certain distinct features. They were found twisted and curled. Some of them had holes pierced through them. Some had both sharp and glancing dents. Their orientation indicated ex- plosive damage from the inside to the outside. Curling was pro- nounced along the fracture edges and at the free ends of the tongues of metal around the holes. The signatures of explosive deformation and fracture described earlier could be readily rec- ognized in these fragments (Fig. 6.11).
Further evidence for explosive damage was provided by the nature of damage to the structure and fittings in and around the
Chapter 6: Explosive Sabotage / 49
Fig. 6.12 Bottom skin of the front cargo hold of the Boeing 747 aircraft, retrieved from the ocean. Source: Ref 11
(a)
(d) (e) (f)
(g) (h) (i)
(b) (c)
Fig. 6.11 Signatures of explosive deformation and fracture on fragments retrieved from the wreckage. (a) Reverse slant. (b) Curled fragment. (c) Curved fragment. (d) Dent. (e) Spalled fragment. (f) Petaling and curling. (g) Spikes along fracture edge. (h) Craters on sheet metal surface. (i) Nondescript fragments
front toilet. Guided by these and by tracing the trajectories of projectiles in the damaged front portion of the aircraft, investi- gators established the inside of the waste towel receptacle below the wash basin in the front toilet compartment as the center of explosion. Thus, by fractography, the primary cause of the acci- dent was proved to be the detonation of an explosive. Damage to the underside and undercarriage of the aircraft was secondary and had taken place as a result of emergency landing at high ground speed.
Accident to a Boeing 747 Aircraft. In 1985, a Boeing 747
aircraft on a scheduled flight from Montreal to London en route to India suddenly plunged into the Atlantic Ocean, about 110 miles off the west coast of Ireland. Using state-of-the-art technology, with the help of a remotely operated unmanned submersible ve- hicle known as a search craft aiding repair and burial (SCARAB) vehicle, originally intended for laying telephone cables beneath the ocean floor, the wreckage was located and its distribution doc- umented by extensive underwater photography and videography. The wreckage was distributed over an area of 15 square miles on the floor of the ocean, 6700 feet deep. After studying a few thou- sand underwater photographs and viewing a few dozen video tapes, about 20 pieces of wreckage considered essential for further laboratory examination were retrieved from the ocean floor, with the help of SCARAB and two ships working round the clock for a few weeks. A large number of small fragments could also be retrieved along with the larger pieces. Study of the disintegrated aircraft indicated maximum damage in the front portion of the aircraft, especially in and around the front cargo hold.
The most mangled piece of wreckage was the bottom skin of the front cargo compartment (Fig. 6.12). Severe damages such as holes and tears were seen at 25 different locations on this piece. This accident was yet another instance where the features on ex- plosively damaged pieces did survive further crash impact forces as well as immersion in seawater for several weeks.
Many of the important signatures of explosive damage were seen in this piece and on several fragments from this region (Fig. 6.13–6.15). Another important evidence was the mode of fracture
Fig. 6.13 Petaling around holes in the bottom skin of the front cargo hold. Source: Ref 11
Fig. 6.14 Curling of metal tongues. Source: Ref 11
Fig. 6.15 Spikes along fracture edge. Source: Ref 11
(a)
(b)
Fig. 6.16 (a) Fracture in a stantion. (b) Radiograph showing metal curling inward. Source: Ref 11
in the fragments thus generated. This produced further evidence for confirming the cause of the two accidents described previously as in-flight explosion (Ref 10, 11).
In this chapter, methods of identifying damages caused by ex- plosive forces have been described. These have helped in the in- vestigation of accidents to aircraft, caused by deliberate detonation of explosives in flight. The principles can be extended to damages on other structures as well.
of a structural member in the front cargo compartment. This mem- ber, referred to as a stantion, is a square tube in which the fracture was followed by the distinct curling of the metal tongue inward, toward the interior of the tube (Fig. 6.16a). This type of inward curling by more than one turn, shown in the radiograph, Fig. 6.16(b), is certainly a shock wave phenomenon.
The most conclusive evidence was provided by metallography. Metallographic examination was carried out on several fragments retrieved from the front cargo area, on petals around holes, on regions adjacent to the spikes, and on regions close to the curl in the stantion. Twins were seen in the microstructure on all of them. Figure 6.17 shows a typical microstructure revealing twins.
To obtain a further confirmation of the earlier conclusions, frag- ments were also produced in the laboratory by deliberately ex- ploding 2024 aluminum alloy sheets and boxes made out of such sheets. All the features described previously could be recognized
Chapter 6: Explosive Sabotage / 51
REFERENCES
1. H.P. Tardif and T.S. Sterling, J. Forensic Sci., Vol 12 (No. 3), 1967, p 247
2. E. Newton, Can. Aeronaut. Space J., Vol 14, 1968, p 385
3. H.P. Tardif and T.S. Sterling, Can. Aeronaut. Space J., Vol 15, 1969, p 19
4. R.D. Barer and T.S. Sterling, Met. Prog., Vol 98 (No. 5), 1970, p 84
5. R.V. Krishnan, S. Radhakrishnan, A.C. Raghuram, and V. Ra- machandran, Investigation of an Aircraft Accident by Frac- tographic Analysis, Advances in Fracture Research, S.R. Val- luri et al., Ed., Pergamon Press, Vol 5, 1984, p 3677
6. A.C. Raghuram, S. Radhakrishnan, R.V. Krishnan, and V. Ra- machandran, Sci. Age, Vol 3 (No. 8), 1985, p 32
7. V.T. Clancey, Can. Aeronaut. Space J., Vol 14, 1968, p 337 8. J.S. Rinehart and J. Pearson, Behaviour of Metals under Im-
pulsive Loads, Dover Publications Inc., New York, 1954, p
171
9. M. Stelly, J. Legrand, and R. Dormeval, Some Metallurgical Aspects of the Dynamic Expansion of Shells, Shock Waves
and High-Strain-Rate Phenomena in Metals—Concepts and Applications, M.A. Meyers and L.E. Murr, Ed., Plenum Press,
New York and London, 1980, p 113
10. R.V. Krishnan, S. Radhakrishnan, A.C. Raghuram, and V. Ra- machandran, Aircraft Accident Caused by Explosive Sabo- tage, Handbook of Case Histories in Failure Analysis, Vol 2, ASM International, 1993, p 3
11. B.N. Kirpal, V. Ramachandran, J.S. Gharia, J.S. Dhillon, J.K. Mehra, B.K. Bhasin, and S.N. Sharma, “Report of the Court of Inquiry Investigating Accident to Air India Boeing 747 Aircraft VT-EFO, Kanishka on 23 June 1985,“ New Delhi, 1986
Fig. 6.17 Microstructure of a fragment from the front cargo compartment showing twins. Source: Ref 11