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N° 33–1996: Ariane 501 - Presentation of Inquiry Board report

23 July 1996

On 4 June 1996 the maiden flight of the Ariane 5 launcher ended in a failure. Only about 40 seconds after initiation of the flight sequence, at an altitude of about 3700 m, the launcher veered off its flight path, broke up and exploded.

Mr Jean-Marie Luton, ESA Director General, and Mr Alain Bensoussan, CNES Chairman, immediately set up an independent Inquiry Board (see ESA-CNES Press Release of 10 June 1996), which has now submitted its report.

The report begins by presenting the causes of the failure, analysis of the flight data having indicated:

A chain of events, their inter-relations and causes have been established, starting with the destruction of the launcher and tracing back in time towards the primary cause. These provide the technical explanations for the failure of the 501 flight, which lay in the flight control and guidance system. A detailed account is given in the report, which concludes:

" The failure of Ariane 501 was caused by the complete loss of guidance and attitude information 37 seconds after start of the main engine ignition sequence (30 seconds after lift-off). This loss of information was due to specification and design errors in the software of the inertial reference system. The extensive reviews and tests carried out during the Ariane 5 development programme did not include adequate analysis and testing of the inertial reference system or of the complete flight control system, which could have detected the potential failure."

Despite the series of tests and reviews carried out under the programme, in the course of which thousands of corrections were made, shortcomings in the system approach concerning the software resulted in failure to detect the fault. It is stressed that alignement function of the inertial reference system, which served a purpose only before lift-off (but remained operative afterwards), was not taken into account in the simulations and that the equipment and system tests were not sufficiently representative.

Without implicating the system architecture, the report makes a series of recommendations for ensuring that the launcher's software operates correctly. The Ariane 5 programme will be taking action in line with all these recommendations, as follows:

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