2013 Embraer ERJ 170-100 LR External Power Connection Incident at Nuremberg

Incident Overview and Aircraft Details On 13 March 2013, an Embraer ERJ 170-100 LR, a twin-engine commercial aircraft with a maximum takeoff mass of 37,200 kg, landed at Nuremberg Airport at approximately 10:45 local time. The aircraft, which was French-registered and operated by a French airline, was carrying 77 passengers and four crew members. The flight had been uneventful until the aircraft reached its parking position. ## Sequence of Events A few minutes after the aircraft was parked and the ground power supply was connected, a hissing sound was heard inside the aircraft, and the ground power supply automatically disconnected. An electrical smell was then detected in the cockpit, followed by visible smoke. The pilot-in-command instructed the ground crew to bring the passenger stairs to the aircraft as quickly as possible, and the passengers were asked to disembark immediately via the normal stairs. ## Investigation Findings The German Federal Bureau of Aircraft Accident Investigation (BFU) investigated the incident. The aircraft's external power connection, located on the underside of the fuselage to the left of the nose gear, was found to have no external damage. However, the inside of the connection was covered with melted material, and the connection cables and the circuit breakers above the connection were soot-blackened. The cable bundles running above the connection were also soot-blackened, and the insulation of the pipes was heat-damaged. ## Component Analysis The individual parts of the external power connection (P/N MS90362-3) were examined after removal. It was found that the bolts, cable lugs, and nuts of the connections A, B, and C for the AC phases were melted on the sides facing each other. The three circuit breakers showed heat damage, and their housings were broken. No traces of heat or high currents were visible inside the housings. The insulation mats of the fuselage installed above the connection also showed heat damage. The pins of the connection had no visible damage. ## Ground Power Supply and Fleet Check The ground power supply was checked by the airport's workshop, and no defects were found. The reason for the check was the device's shutdown with the fault message “Generator Short Circuit.” According to the device's manual, the reason for this message is a short circuit detected by the power control. Since the device worked flawlessly during the check, the inspector concluded that the short circuit must have been on the aircraft side. The airline conducted a visual inspection of the external power connections on all its Embraer jets after the incident. The covers were also removed and checked for foreign objects. 25 aircraft were inspected, and in 13 cases, metal parts were found. These included metal shavings, washers, screws, etc. The European Aviation Safety Agency and the holder of the aircraft's type certificate were informed of the findings by the airline and the BFU, respectively. ## Safety Recommendations The aircraft manufacturer, in its capacity as the holder of the type certificate, issued SB 170-24-0057 on 30 September 2015, describing how the upper openings of the external power connection cover could be closed to prevent short circuits caused by foreign objects. Due to these measures, the BFU refrained from issuing a corresponding safety recommendation.