Aviation Investigation Report A98H0003
1.12.1 Wreckage Recovery
22.214.171.124 General (STI1-61)
The search and rescue response to the event was immediate, and included resources from the Canadian Forces (CF) (Department of National Defence (DND)), Canadian Coast Guard (Department of Fisheries and Oceans), the Royal Canadian Mounted Police (RCMP) (Department of the Solicitor General of Canada), and numerous private individuals in boats from the local area. An exclusion zone was put in place to protect the site and to provide security during recovery operations. The exclusion zone was removed on 1 November 1999. Until that time, there was continuous security in place, and no known breaches of security occurred. Recovery and sorting of the wreckage took approximately 15 months to complete.
The wreckage site was located when the submarine HMCS Okanagan homed in on the underwater locator beacons (ULB) from the flight recorders. Various ship-borne underwater imaging technologies, divers, and video cameras on remotely operated vehicles (ROV), provided information about the wreckage condition and dispersion. The main debris field measured approximately 125 by 95 m (411 by 312 feet). The water depth was about 55 m (180 feet).
The focus of the initial recovery phase was on finding and recovering human remains, and on locating the CVR and the FDR. Extensive surveillance of the wreckage field and the surrounding area was completed to assess the various recovery options. Floating wreckage was scattered by wind and water currents, but no major piece of wreckage was found outside the confines of the irregularly shaped, single debris field on the seabed. Some of the wreckage recovery methods, as described in the sections that follow, spread wreckage over a wider area.
Wreckage recovery operations yielded over 126 554 kg (279 000 lb) of aircraft material, which represented approximately 98 per cent of the structural weight of the aircraft. Over 18 144 kg (40 000 lb) of cargo was also recovered.
126.96.36.199.1 Initial Wreckage Recovery Methods (STI1-62)
Initial wreckage recovery activities included collecting debris from the surface of the water, searching shorelines, shallow water dive operations near shoreline areas, and deep dive operations at the debris field.
Divers from the Canadian Navy recovered the FDR on 6 September 1998 and the CVR on 11 September 1998. There was some delay in recovering the first recorder because both recorders were equipped with water-activated ULBs that were transmitting on the same frequency. Once the general area of the beacon signal was located, it was difficult to pinpoint the precise location of either of the recorders.
The ULB attachments were damaged to the extent that they had nearly become detached from the recorder. There is no regulatory requirement that the recorders be tested and certified with the ULBs attached.
Beginning on 12 September 1998, the USS Grapple, a United States Navy (USN) salvage ship, was on site for approximately three weeks, adding additional lift, dive, and ROV capabilities.
The continued use of divers to recover wreckage was assessed as hazardous owing to increasingly inclement weather; deteriorating sea state conditions; water depth; and the sharp, jagged state of the wreckage. It was also recognized that at the rate the wreckage could be recovered using this method, the majority of the wreckage would not be recovered in a timely manner, and that higher-capacity methods would have to be employed.
Between 6 804 and 9 072 kg (15 000 and 20 000 lb) of material was recovered during the initial recovery operations.
Between 13 October and 24 October 1998, two contracted barges, moored together, were used to recover material from the debris field (see Figure 18). A heavy lift crane on the deck of one barge scooped wreckage from the seabed and placed it on the deck of the second barge, where it was sorted and washed. The wreckage was then transported to shore by CCG ships for further processing.
Approximately 68 040 kg (150 000 lb) of wreckage was recovered using this method.
A scallop dragger was used from late October 1998 to mid-January 1999. A scallop rake that was towed behind the vessel scraped the seabed and collected material into a chain-link mesh net. Working 24 hours per day when the sea conditions were suitable, 1 839 tows were completed.
Approximately 34 020 kg (75 000 lb) of wreckage was recovered using this method.
Various ROVs were used throughout recovery operations to provide reconnaissance and recovery capability. A laser line scan and side scan sonar survey was performed to determine the extent of wreckage distribution and to provide detailed information about the seabed. Following the scallop dragger operation, the recovery area was prepared for the next phase by using ROVs to video tape the seabed in and around the site of the debris field. A CF ROV, called the Deep Seabed Intervention System, was used from 26 April 1999 to 14 July 1999 to recover material that would not be suitable for recovery by the planned suction dredge ship method.
Approximately 2 268 kg (5 000 lb) of wreckage was recovered during these operations, and considerable information about the type and location of the remaining debris was acquired.
The final phase of wreckage recovery was conducted in the fall of 1999. It involved dredging the area of the debris field to a depth of about 1.5 m (5 feet) to recover the remaining debris. The dredged material was pumped into the vessel's hopper and transported to Sheet Harbour, Nova Scotia, where it was off loaded into a prepared containment area.
The dredged material was then processed through a mechanical sifter to sort it by size, and deposit it on conveyor belts. The aircraft-related debris was then separated from the other material by hand as it passed by on conveyor belts. About 12 701 kg (28 000 lb) of wreckage was recovered using this method.
The sifting and extraction of aircraft wreckage at Sheet Harbour was completed on 3 November 1999, and the subsequent sorting of this recovered debris was completed on 4 December 1999, 15 months after the occurrence.
- Date de modification :
- Date modified: