Two maintenance engineers and their supervisor have been charged with manslaughter by the Spanish judge in charge of the judicial inquiry into the 20 August Spanair Boeing MD-82 take-off accident at Madrid Barajas airport, in which 152 of the 172 people on board perished.
The technical inquiry's interim report indicates that the probable cause of the crash was that the crew, having failed to set the flaps and slats to their take-off setting, were not alerted to the omission because the take-off configuration warning did not sound as they applied power to accelerate.
The maintenance engineers were interviewed by the judge because they took action to correct a problem the pilots had reported, and the implication is that their action may have had a bearing on the failure of the take-off configuration warning system to operate.
The pilots had taxied back from their first attempt at take-off because, according to the interim report, they "had detected an overheating ram air temperature probe [RATP], and noted this in the aircraft technical log book [ATLB]".
The report by the Spanish technical investigators continues: "The aircraft returned to the apron...stopped the engines and requested assistance from maintenance technicians to solve the problem. The mechanic confirmed the malfunction described in the ATLB, checked the RATP heating section of the minimum equipment list and opened the electrical circuit breaker that connected the heating element. Once complete, it was proposed and accepted that the aircraft be dispatched."
Electrical circuits normally supply heat to the RATP only when the aircraft is airborne, activated or deactivated via a weight-on-wheels sensor in the nose-gear. The probe shares an electrical link with the configuration-warning system, as well as other functions, through a relay designated R2-5. But according to the interim report, the minimum equipment list consulted the engineers before tripping the RATP circuit breaker permitted that action.
Whether other checks beyond the list were also required, or whether there was an undiscovered electrical circuit logic fault, is not covered in the interim report.
In Spain, as in most countries, a judicial inquiry and action to prosecute individuals runs parallel to the technical inquiry, despite the fact that this contravenes the state's obligations under Chapter 13 of the International Civil Aviation Organisation's Chicago Convention, which sets global standards for aviation practice.