Acoustic search of aircraft CVR/FDR in the ocean floor using USBL/SSBL hydroacoustic positioning systems: Results achieved in real environment operational tests

In August 2011 a helicopter model AW-139 manufactured by AGUSTA WESTLAND crashed in Campos Basin in Pampo Oilfield area at a depth of approximately 100 meters. Unfortunately there were no survivors. Petrobras sent a fleet of 12 RSV and PLSV vessels for the localization of the aircraft´s wreckage in order to recover the bodies and investigate the causes of the accident. After vessels mobilization and approximately 36 hours of search, the wreckage was finally found and the geographical position determined. The ICAO (International Civil Aviation Organization) Annex 6 [4], states that the so-called "black boxes" - CVR (Cockpit Voice Recorder) and FDR (Flight Data Recorder) shall have acoustic devices to allow their localization in case of submersion. It has been agreed on the use of acoustic pingers following AODC standards (Association of Offshore Diving Contractors) whose signal output frequency is 37.5 kHz, resistance to water depths up to 6096 meters and minimum battery life of 30 days. The USBL hydroacoustic positioning systems (Ultra Short Base Line) installed in RSV, PLSV and AHTS vessels are manufactured mostly by the companies Kongsberg and Sonardyne and are designed to operate within a frequency band from 19 to 36 kHz. However, it is possible to detect a frequency of 37.5 kHz with some limitations. This detection capability was unknown to hydroacoustic systems operators at the time of the mentioned accident, which could have substantially, speed up search and salvage operations. Petrobras then began a series of tests in some RSV vessels in order to determine the operational limits of hydroacoustic systems in CVR/FDR pinger detection during SAR operations of wrecked aircraft in the ocean floor. The purpose of this paper is to describe these tests and results.