Jet2 B733 at East Midlands on Sep 3rd 2014, electrical problems resulting in smoke in cabin
Last Update: August 14, 2015 / 20:23:26 GMT/Zulu time
Passengers reported the aircraft went around just prior to touch down and landed on its second round, it appeared however the (public) audio system had failed during the second approach. While taxiing towards the terminal a burning smell became obvious and smoke appeared in the cabin.
The airline reported electrical problems resulted in smoke in the cabin and a precautionary evacuation.
The United Kingdom's Air Accident Investigation Branch (AAIB) reported a serious incident at East Midlands by an airliner in the evening of Sep 3rd 2014 and dispatched an investigation team on site.
In the evening of Sep 4th 2014 The Aviation Herald received information indicating first preliminary examination of the aircraft suggests the electrical problem was related to relay R1. That relay R1, connecting the Battery Busbar, had already caused two incidents on Boeing 737-300 G-EZYN on Mar 22nd 2005, AAIB investigation report and on Boeing 737-300 G-THOJ on Aug 13th 2006, AAIB investigation report. In both occurrences the crew had noticed progressive abnormal announciator indications, one crew up to and including the loss of the DC Battery Bus and loss of standby ADI. As result of the investigation into G-EZYN a safety recommendation 2005-65 had been issued which was also directly relevant to G-THOJ according to AAIB findings and may, according to current information, also be relevant to G-GDFT. Safety recommendation 2005-65 reads: "It is recommended that the Federal Aviation Administration require that the Boeing Airplane Company examine the various electrical configurations of in-service Boeing 737 aircraft with the intention of providing operators with an Operations Manual Procedure that deals with loss of power from the Battery Busbar." The AAIB had analysed for G-EZYN: "The loss of the Battery Bus on Boeing 737-300/400/500 aircraft results in the loss of a number of significant systems which, on some aircraft, can include the Standby Attitude Indicator. The integrity of the main attitude displays on EFIS equipped aircraft can also be compromised due to the loss of cooling." and stated: "Checklist procedures for electrical system malfunctions cannot reasonably be expected to cater for failures of individual components down to relay level, so the crew were left to conduct their own diagnosis. This they did successfully, to the extent that they identified zero volts on the Battery Bus and the static inverter. However, there were no drills for this condition so they took no additional action, although normal operation, at least on this aircraft, could have been restored by moving the Standby Power switch to the ‘BAT’ position."
On Aug 14th 2015 the AAIB released their final report concluding the probable cause of the serious incident was:
The electrical difficulties experienced in this aircraft were as a direct result of the loss of continuity between the R1 relay terminals. This was due to one of its terminals loosening in its insulated mounting over an indeterminate period of time and moving away from the contactor, thus breaking continuity. It is possible that this was caused by an overtightened terminal nut weakening the terminal and insulator soldered joint whilst at the same time being under a degree of tension or side load from the heavy gauge electrical cables.
The AAIB reported that the aircraft was descending towards East Midlands when the commander wanted to make an announcement to the passengers and realized the PA System had failed. The AAIB wrote: "The flight crew then noticed indications of other, seemingly unconnected, failures which included faults with: the left equipment cooling fan; a radio; the weather radar; the autobrake; and the power supply to the standby attitude indicator and standby compass. In addition, indications of terrain, reference speeds, engine fuel flow and N1 (low speed compressor) rpm disappeared from the pilots’ displays. The crew discussed the situation, diagnosed that the aircraft had a problem with the battery busbar, but commented that there were no Non-normal Checklists (NNC) in the Quick Reaction Handbook (QRH) to help them. They also noted that the battery on its own was capable of providing power to systems for approximately 30 minutes. The commander told ATC that the aircraft had suffered a partial electrical failure and asked for expeditious routing to East Midlands Airport."
The flight crew aborted the first approach as there were no indications of the status of the landing gear. A low approach did not succeed in establishing whether all gear was down due to darkness. While positioning for another approach the first officer used the observation ports in the floor of the main cabin and determined that all gear was down and locked. The aircraft landed safely and taxied towards the stand, when cabin crew in the forward cabin smelt smoke and observed mist rising near the overwing exit doors. In the meantime the flight crew also observed an acrid smell in the cockpit, hearing the lead flight attendant knock the door (as she could not contact the cockpit due to the failure of the interphone) the flight crew opened the door and instantly thought the smell had become worse. Smoke detectors activated throughout the aircraft, the crew declared Mayday and initiated an emergency evacuation.
The AAIB summarised: "The pilots were not sure whether the battery was discharging and did not know which additional systems would be lost if it discharged fully. Despite the fact that both engine driven electrical generators were functioning normally, the pilots decided that it would be sensible to attempt to land within 30 minutes from when the symptoms were first observed. This was because they expected a fully charged battery to be able to power connected systems for at least 30 minutes. Despite uncertainty over the exact nature of the failure, the pilots were content that they knew which systems would be unavailable during the landing."
The AAIB analysed: "The reproduction of the electrical power distribution system symptoms after the incident and the rectification by replacement of the R1 relay, confirmed the failure of the R1 relay as being causal. In order to lose power to the battery bus there needs to be a loss of continuity between the A or B terminals; for this to happen one or both of the terminal post must be permanently misaligned or become ‘out of reach’ of the contactor plate. The continuity checks in situ, with power off, (ie the relay in a de-energised condition) were inconclusive, probably due to the terminals being loose. Forensic examinations by an independent laboratory and by the OEM offered differing conclusions as to why the terminals became loose. ... Previous incidents have shown that a secondary effect of the R1 relay failure can result in smoke within the cabin and cockpit. The loss of the DC Bus causes the R320 ground sense relay to drop out causing the ACM cooling turbo fans to stop. Without the forced air cooling, the ACM will overheat over a period of time as it is in constant receipt of heated air from the engine compressor. As a result any oil residue and dust within the ACM and ducts will start to produce vapour, smoke and fumes. The examination of the ACMs showed that the lubricating oil in the sight glasses appeared to be discoloured and overheated indicating the possibility of heat distress."
This article is published under license from Avherald.com. © of text by Avherald.com.
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