West Atlantic B734 near East Midlands on Oct 12th 2018, electrical failures

Last Update: September 5, 2019 / 16:14:35 GMT/Zulu time

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Photo of West Atlantic G-JMCR, Boeing 737-400 — West Atlantic G-JMCR, Boeing 737-400 (Photo credit: Alec BHX/KKC / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Oct 12, 2018

Classification
Report

Airline
West Atlantic

Flight number
QY-1444

Departure
Amsterdam, Netherlands

Destination
East Midlands, United Kingdom

Aircraft Registration
G-JMCR

Aircraft Type
Boeing 737-400

ICAO Type Designator
B734

A West Atlantic Boeing 737-400 on behalf of EAT Leipzig, registration G-JMCR performing flight QY-1444 from Amsterdam (Netherlands) to East Midlands,EN (UK) with 2 crew, had been dispatched with the left hand generator (Gen #1) inoperative under minimum equipment list requirements, the APU was providing electrical power instead together with the right hand generator (Gen #2). The aircraft had just begun the descent into East Midlands when the crew experienced an unusual array of electrical failures, however, managed to perform a safe landing at East Midlands despite numerous degraded and failed systems.

On Sep 5th 2019 the AAIB released their final report concluding the probable causes of the serious incident were:

This serious incident was caused by the incorrect racking of generator control unit (GCU) 2 which moved forward in flight initially causing an intermittent and then total disconnection of the electrical connector. The aircraft was not designed to operate with the GCU disconnected and the crew were presented with an unusual situation that was not covered in the QRH.

The activities surrounding the management of the faults on G-JMCR during the previous 12 days, and the actions of the crew in handling the emergency, indicates a weakness in the operator’s policies and procedures for the management of risk. Engineers were not always given sufficient time to investigate the faults, with the result that fault finding was often repeated and not finished. Work at a number of locations was not recorded as having been carried out in the aircraft documentation. The aircraft was dispatched from its main operation base with an ADD and flew through a number of locations where it could have been cleared, which was contrary to the procedures in the Operation Manual.

Communication between LMC, the commander and the Part 145 organisation at Amsterdam was ineffective in highlighting the underling technical problems on the aircraft. The engineer was unaware of the full history of the faults and the concerns that LMC conveyed to the commander that there was a “serious electrical fault on the aircraft”. The engineer was tasked with resetting the generators and spent less than 30 minutes at the aircraft. Despite the ongoing concerns with the electrical systems previously raised by a number of engineers and crews, and the unusual set of failures that occurred during the landing at Amsterdam, LMC did not carry out any form of risk assessment or ensure a deeper investigation was carried out before the aircraft departed Amsterdam. While the commander had the ultimate decision on accepting the aircraft, he was new to the company and may have relied on the advice of the engineers without being aware that the engineer had only been tasked with resetting the generators.

The operator had previously identified that there was a need to restructure LMC, introduce the post of Defect Controller and provide staff with further training to improve their competency.

The AAIB reported the aircraft had originated in Leipzig and was flying to Amsterdam. The AAIB described the following sequence of events:

At 2243 hrs, the aircraft departed from Leipzig and the flight was without incident until the landing at Amsterdam when the co-pilot’s flight instruments, which are powered by the No 2 electrical system, intermittently blanked and several electrical warning lights on the overhead panel illuminated intermittently. The crew were unable to determine the cause of the problem and concluded that Gen 2 had failed, leaving the APU generator providing the only electrical power to the AC busses. They attempted to select the APU generator to provide power to the No 2 electrical system, but it would not connect. The aircraft was taxied to the parking stand and shut down.

The crew were aware that the MEL did not allow the aircraft to dispatch with only a single generator functioning and, therefore, the crew contacted the operator’s Line Maintenance Control (LMC) who arranged for an engineer in Amsterdam to attend the aircraft. After around 30 minutes, the engineer arrived at the aircraft and was briefed by the commander. He was seen to open the cowlings on the right engine in order to examine Gen 2; he also checked the relevant circuit breakers and Panel M238 on the sidewall of the cockpit. The engineer informed the crew that he had reset a circuit breaker and was confident that this was the cause of the problem but would require the right engine to be run in order to ensure that the engine generator was working correctly. The engine run was performed satisfactorily and the generator on the right engine and the No 2 electrical system worked normally. The engineer cleared the entry in the aircraft technical log and as part of their pre-flight preparation the crew discussed the actions they might take in the event they lost the remaining engine generator. The aircraft departed Amsterdam with the original ADD for an inoperative Gen 1.

The flight was without incident until the aircraft was approximately 60 nm from East Midlands, with the co-pilot as PF, when during the descent the autopilot disconnected, the co-pilot’s screens lost power and his flight instruments failed. The commander took control and disconnected the autothrottle as he was flying the aircraft manually. Numerous lights on the overhead panel and system annunciation panels illuminated and flashed, and multiple aural warnings were generated by the Terrain Avoiding Warning System (TAWS). As both crew members were visual with the runway, the commander instructed the co-pilot to make a PAN call and ask for vectors straight onto the ILS at East Midlands. During the next 20 minutes, and until the aircraft landed, the flight instruments on the co-pilot’s side came on and off numerous times.

The commander manually flew an ILS approach onto Runway 27. The aircraft controls, flaps and gear worked normally although the distracting flashing warning lights and aural callouts continued throughout the approach. On landing, numerous aircraft systems failed including the autobrakes (although manual braking remained available), half the exterior lights and the commander’s speed indications on his electronic attitude display indicator. On reaching the stand, the crew were unable to connect the electrical ground power to the aircraft system. While the flaps were retracted, the flap indication showed them still deployed. No electrical power was available to the cargo door, cargo bay and multiple items on the flight deck.

The crew briefed the ground engineers and completed the technical log before continuing to Aberdeen on a replacement aircraft. The engineers later discovered that the GCU for Gen 2, which is located in the flight deck behind the right pilot seat, was not correctly fitted in its housing.

The AAIB describe maintenance activities prior to the occurrence, the aircraft was having problems with the left hand generator for 12 days:

- On three occasions between 1 and 9 October 2018, GCU 2 had been transposed with either GCU 1 or the APU GCU without any documentation having been raised.

- There had been ongoing electrical problems during the 12 days prior to the incident flight when an electrical fault appeared to transfer from the APU generator system to the No 1 electrical system.

- A number of engineers during this period had recorded that the aircraft needed sufficient downtime to fully investigate the electrical faults.

- On 1 October 2018 the aircraft was allowed to operate in accordance with MEL 24-2a as there was ‘insufficient time’ to investigate multiple electrical failures on the ground when the APU generator was on-line.

- On 5 October 2018, an ADD in accordance with MEL 24-1b was raised for ‘GEN 1 tripping TRU 1’, while the aircraft was at the operators main engineering base at East Midlands without the engineers having determined the cause of the fault.

- On 11 October 2018, an RIE was authorised to extend the ADD for Gen 1 without the engineers having identified the cause of the electrical failures.

- On six occasions during the 12 days preceding the incident flight it appears that fault finding was either stopped or not started as there was insufficient time during the turnaround to carry out the work.

- During these 12 days the aircraft frequently passed through locations where there were sufficient maintenance resources to identify the cause of the electrical faults and clear the ADD.

The AAIB analysed:

Cause of the electrical failures

The electrical failures that occurred during the landing at Amsterdam and on the subsequent flight to East Midlands were caused by GCU 2 moving forward in its rack far enough to cause the electrical connectors to disconnect. The flickering lights and screens indicate that initially there was a partial connection that was intermittent, but on landing at East Midlands the GCU appears to have moved forward sufficiently for the connector to fully disconnect. This would have resulted in the loss of: Gen 2; Gen Bus 2; Transfer Bus 2; 115V AC Electronic Bus 2; 28V DC Bus 2; and 28V DC Electronic Bus 2. Electrical System 1 would still have been powered by the APU generator through Gen Bus 1.

The Boeing 737-400 is not designed to operate with the GCU disconnected. While there was no record in the aircraft technical log or worksheets for the previous 12 days of GCU 2 having been disturbed, messages on the company’s FSR stated that it had been disconnected on three occasions during this period as part of the fault finding to clear the ADD on the left engine generator.

Management structure

Since November 2017 the operator had experienced a number of significant changes. There had been an increase of approximately 30% in the number of aircraft and staff with the operator’s main operating base and LMC moving from Coventry Airport to East Midlands Airport. The administration of the AOC and Part M responsibilities also moved from Coventry Airport, to a nearby business park. The operator’s own audit recognised the need to change the management structure of LMC and improve the management of defects and the competency of the staff within the LMC. This serious incident occurred during this transition period.

Flight crew performance

At no stage during the event did the flight crew consult the QRH or attempt to analyse the fault. They did not use either the operator’s suggested decision-making tool DODAR nor any other tool. Given the good weather conditions, the point in the flight when the failure occurred, and the availability of a long runway at East Midlands, the crew were able land the aircraft safely with few issues. Had the crew performed some kind of analysis and discussed options for a safe landing, it is likely that they would have decided that landing at East Midlands was still the safest option.

If the aircraft had been in cloud, with poor weather conditions on the ground, the crew would have faced a challenging recovery with little automation available and with the co-pilot unable to monitor the flight path of the aircraft. The use of a suitable decision-making tool, such as DODAR, would have aided the crew in analysing the problem and agreeing a suitable solution. It would also have prompted them to consider what systems may have been inoperative, and its effect on the approach and aircraft’s landing performance. Although the time available to the crew was only around 15 minutes, this was long enough for such an analysis to be performed without delaying the approach and landing.

Use of the MEL and RIEs

The operator did not appear to use the MEL in the spirit of EASA’s Acceptable Means of Compliance or its own procedures. Rather than using the MEL to allow the aircraft to return to its main operating base where the faults could be rectified, it appears to have been used to enable the aircraft to meet operational commitments. Fault finding, and rectification was frequently stopped before the root cause had been identified and on a number of occasions the aircraft was dispatched from a location where the work could have been carried out. The burnt pins on the feeder cable was a known fault. On 10 October 2018, an engineer correctly identified that there was a FF on Gen 1 and inspected the connector between the engine and pylon but ran out of time to check the connector between the pylon and wing where the burnt pin was located.

The RIE for the defect on Gen 1 should only have been granted in exceptional circumstances. However, while resources were available to identify and fix the fault within the specified time, the RIE was approved to enable the operator to meet operational commitments.

There also seemed to be confusion with operations and engineering staff within the LMC and the Part M organisation as to what constituted a main operating base. It was commonly believed that a number of locations across their operating network that had Part 145 organisations could be considered as a main operating base and that it was acceptable for aircraft to be dispatched from East Midlands with an ADD operating in accordance with the limitations in the MEL. This was, however, contrary to the operator’s Operation Manual.