France A320 at Bastia on Sep 11th 2016, ground worker electrified
Last Update: December 13, 2020 / 17:45:36 GMT/Zulu time
The occurrence aircraft was able to depart for the return flight with a delay of 30 minutes and reached Paris with a delay of 15 minutes.
The French BEA reported on Sep 22nd 2016, that the occurrence was rated an accident. The ground worker was electrified when connecting the GPU and received serious injuries.
The French BEA released their final report concluding the probable cause of the accident was:
The absence of insulating sheath on the end of the cables of the ground power connector was probably due to damage to the connector:
- following repeated pulling on the cables and not on the connector body to remove the connector or
- following the incident of 22 June 2016.
The absence of sheath led to a short circuit at the three phases of the connector when the latter was plugged into the aircraft receptacle and supplied with power by the simultaneous actuation of selector switch S10.
The BEA summarized the sequence of events:
After the aircraft had come to a standstill on the apron, the ramp agent(2) positioned the chocks on the nose landing gear and then on the main left landing gear after engine shutdown and informed the crew of these actions via the ground interphone connection. The crew informed him that the parking brake was released. The ramp agent checked that the aircraft was stabilized, reported this to the crew and authorized the ground support equipment to be brought forward and the docking of the jetways.
He went to the Ground Power Unit (GPU) whose engine was already in operation, picked up the connecting cable and got ready to connect the ground power connector to the aircraft. As the cable was tangled up, he was not able to do this and asked a ground attendant(3) to untangle it. He then connected the ground power connector to the aircraft. At this moment, witnesses heard an explosion, the ground attendant saw an electric arc of around 30 cm at the connector and the ramp agent was thrown to the ground. The connector stayed connected to the aircraft.
The ramp agent was quickly cared for by the emergency services. The diesel engine of the ground power unit was shutdown.
The BEA described the injuries: "The ramp agent had injuries to his right ear and left thigh linked to the explosion and to his subsequent fall to the ground. He had no burn marks."
The BEA reported a previous incident: "On 22 June 2016 the GPU was involved in an incident. The ramp agent started the tractor without having first removed the GPU tow bar which led to the GPU being moved while it was still connected. It was observed that the GPU ancillary panel on the aircraft was damaged. It was checked and repaired. No action was carried out on the GPU."
The BEA pointed out lessons learned as result of the occurrence:
Mechanical action on selector switch S10 simultaneous with connection of connector to aircraft
The fusion of the phase and neutral cables was necessarily the result of power being present in these cables and the existence of an electrical contact between them.
As no defect was observed on the aircraft’s ground power receptacle and electrical panel, it was possible to rule out that power was supplied due to a malfunction at the aircraft which would have supplied these cables when they were connected and before the supply of the three-phase current produced by the GPU.
The presence of the three-phase power supply on the connector initially required selector switch S10 to be set to the «CLOSE» position whether or not the connector was connected to the aircraft.
The self-hold of selector switch S10 at «ON» allowing the three-phase supply depended on the actual connection of the connector to the aircraft, as selector switch S13 was found in the «AIRCRAFT OUTPUT» position.
In a situation where the phase and neutral electrical cables in the connector touch each other, the short circuit occurs as soon as a 115 V power supply is applied to the connector, in other words, as soon as the «CLOSE» position of selector switch S10 is used, regardless of whether the connector is connected or not to the aircraft.
Given that the «CLOSE» position of selector switch S10 is spring-loaded when the connector is disconnected, closing the circuit requires this switch to be mechanically held in position for a certain time.
It was established that this mechanical action was concomitant with the connection of the connector to the aircraft, as the connector remained inserted after the short circuit. The probability of such a concomitance in the absence of a voluntary action by another person is therefore very low.
The investigation was not able to determine who had actuated the selector switch.
Comparison of risks relating to connecting and disconnecting connector to and from aircraft
In the event of the disconnecting procedure being shortened, physically disconnecting the connector is sufficient to cut off the power supply even when S10 is set to «ON». Mechanically setting the selector switch to the «OFF» position aligns the position of the selector switch with the position of the actual supply control. Ground operators may therefore perceive this as a double safety measure and not necessarily see the importance of the sequence proposed by the disconnecting procedure, all the more so when it requires the operator to go back and forwards between the GPU and the aircraft several times.
Conversely, holding the switch in the «CLOSE» position does not provide this redundancy, this single action immediately supplying the connector.
Any deviation from the procedure for connecting the connector to the aircraft with the intention of anticipating the action on selector switch S10 leads to a particularly dangerous situation for all the personnel who are directly or indirectly exposed.
It is therefore essential to recall that:
- before connecting a GPU to an aircraft, the operator must check that the switch is actually in the «off» position;
- only one agent connects the connector to the aircraft and this same agent then supplies the aircraft with electricity.
This article is published under license from Avherald.com. © of text by Avherald.com.
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