Canada E190 near Toronto on May 25th 2016, fire in avionics bay
Last Update: September 11, 2017 / 15:14:55 GMT/Zulu time
The Canadian TSB reported that maintenance found extensive fire and smoke damage to the Right Integrated Control Center (located in the electronics bay aka avionics bay). However, there was no cockpit indication of fire or smoke as there is no detection capability in that area. An investigation into the occurrence has been opened.
On Sep 11th 2017 the TSB released their final report concluding the probable causes of the incident were:
- At some point, a fluid contaminant came into contact with the top of the right integrated control centre. It could not be determined exactly when or how it was introduced into the avionics compartment.
- The fluid contaminant came into contact with electrical components in one of the alternating current bus bars. This caused arcing, which led to smoke and fire. The resultant failures eventually disabled the main electrical system.
- Within 36 seconds of the initial fault, power was lost to all main bus bars and, as a result, the smoke detector in the recirculation bay and the recirculation fans lost power.
- The smoke that had developed during this time did not travel through the recirculation ducts and onto the detector in a sufficient quantity to trigger a warning before the power supply to the detector was lost.
- Without power, the recirculation fans did not transfer air between the middle avionics compartment and the cabin; as a result, the smoke did not enter the cabin and was not detected by the crew.
- The flight crew followed the instructions in the Quick Reference Handbook’s electrical emergency checklist and delayed resetting the integrated drive generators until the auxiliary power unit was started. As a result, the smoke detector in the recirculation bay remained unpowered during the period of time when smoke was likely detectable.
- Due to the lack of warning of smoke or fire, the flight crew was unaware of the severity of the situation and elected to continue to destination.
Findings as to risk
- If company policies do not restrict outside fluids in areas where they may cause harm to sensitive equipment, then there is a continued risk of contamination causing component malfunctions or failures.
- If flight crews are not fully aware of the severity of the emergency situation and exercise their discretion as provided in the Aircraft Operating Manual to not land at the nearest suitable airport as prescribed in the Quick Reference Handbook, then there is an increased risk that a flight will be continued to destination when safer options exist.
- If flight crew guidance for electrical emergencies does not include an early evaluation of battery discharge or confirmation of a supplementary power source, then there is an increased risk that battery power will be insufficient to ensure that essential equipment remains powered until the aircraft can be landed.
- If flight crews become aware of a situation that may jeopardize safety, but do not declare an emergency with air traffic control, then there is an increased risk that should the situation worsen, the flight will still be airborne due to a lack of priority handling, or that it will land without emergency services standing by.
The TSB reported that 3 of 5 cockpit panels went dark when the aircraft was enroute at FL360 about 4 minutes after levelling off at FL360, and the crew received EICAS messages "ELEC EMERGENCY", "IDG 1 OFF BUS" and "IDG 2 OFF BUS" amongst other messages followed by additional messages a few minutes later. The RAM Air Turbine deployed and restored electrical power about 7 seconds after the fault. The crew informed ATC of an electrical problem however did not declare emergency, the crew decided first to try to restore electrical power. While working the related checklist an APU start was listed by the checklist, however, the APU is limited to FL300 or below, hence the crew requested a descent. Descending through FL300 the crew started the APU and proceeded with the checklist to bring IDG #1 online and subsequently IDG #2. Full power was restored at the time the aircraft levelled off at FL240.
The electrical fault messages cleared from the EICAS except for the TRU2 transformer rectifier unit, TRU1 powered the systems that would have been connected through TRU2 however.
About 7 minutes after the electrical failure the autopilot was re-engaged. The crew advised they had restored some electrical power but still requested vectors and the longest runway available at Toronto as they were planning to land with reduced flaps. All ATC units involved assigned priority to the flight.
The TSB analysed that a contaminant's conductivity would be higher when it is fluid, however, it would be unlikely that any contaminant would remain liquid longer than 6 hours. However, nobody had entered the compartment during the previous 7 months, access to the compartment would require a ladder. Given the difficulty to enter the compartmen it would be possible a beverage container would be brought in and could remain in there unnoticed for a long time. However, it would be highly unlikely that a fluid in that container would remain liquid for 7 months and not evaporate. In addition, no empty beverage container was found. As result the investigation was unable to determine the source of the contamination.
The TSB analysed:
The fluid contaminant came into contact with electrical components in one of the alternating current bus bars. This caused arcing, which led to smoke and fire. The resultant component failures eventually disabled the main electrical system.
When the initial arcing began, various systems began to record faults and smoke began to accumulate in the middle avionics compartment. Within 36 seconds of the initial fault, power was lost to all main bus bars and, as a result, the smoke detector in the recirculation bay and the recirculation fans lost power.
The smoke that had developed during this time did not travel through the recirculation ducts and onto the detector in a sufficient quantity to trigger a warning before the power supply to the detector was lost. Without power, the recirculation fans did not transfer air between the middle avionics compartment and the cabin; as a result, the smoke did not enter the cabin and was not detected by the crew.
Once the main power was lost, the smoke likely began to vent overboard from the recirculation bay through the outflow valve, which remained powered through the essential bus. By the time power was restored to the smoke detector when the No. 1 integrated drive generator (IDG 1) was reset, almost 10 minutes later, the smoke had likely dissipated to a level that was no longer detectable.
Because the flight crew received no warning of smoke or fire, they were unaware of the severity of the situation and elected to continue to destination.
The TSB analysed the checklists:
The first action item on the QRH checklist is to start the aircraft’s auxiliary power unit (APU). Although the checklist did not state the maximum altitude at which the APU can be started, the crew knew this limit and did not attempt to start it when they were at 36 000 feet; instead, the crew initiated a descent. Because the aircraft was being operated in visual meteorological conditions and had numerous systems disabled, including the autopilot, the crew decided to complete this descent at a moderate, rather than rapid, rate.
The next 2 items on the QRH checklist covered re-cycling the IDG selectors. The crew understood the order of the checklist items to mean that they should be completed only after the crew had attempted to start the APU. Because the aircraft was being operated above the altitude limit for starting the APU, this checklist sequence resulted in a period of nearly 10 minutes during which the aircraft was without its main power supply while it descended to an altitude at which the crew could attempt to start the APU.
If the main power supply had been restored sooner by re-cycling the IDG selectors shortly after the failure, the re-powered smoke detector may have provided a warning of the fire and smoke, and the crew could have escalated the urgency of their response.
However, the flight crew followed the instructions in the QRH’s electrical emergency checklist and delayed resetting the IDGs until the APU had been started. As a result, the smoke detector in the recirculation bay remained unpowered during the period of time when smoke was likely detectable.
The next item on the QRH checklist is to evaluate battery discharge and possibly manually deploy the RAT. In a situation where the RAT does not deploy or is not able to provide power, aircraft batteries have been demonstrated to supply power to the essential buses for at least 10 minutes. However, further power supply beyond this time is uncertain.
In the unlikely event that the RAT does not deploy successfully after an electrical emergency, and the crew, following current checklist guidance, waits to attempt to start the APU for a similar amount of time, it is possible that the batteries would be depleted and would no longer provide power to the essential buses. In addition, the depleted batteries would not be able to start the APU. In this condition, if the crew did not reach the step in the QRH procedures to re-engage the IDGs, it would be significantly less likely for safe flight to continue, because there would be no engaged source of electrical power.
If flight crew guidance for electrical emergencies does not include an early evaluation of battery discharge or confirmation of a supplementary power source, then there is an increased risk that battery power will be insufficient to ensure that essential equipment remains powered until the aircraft can be landed.
The TSB analysed with respect to declaring emergency:
In addition to the decision to continue to destination, the crew’s perception that an emergency existed only if the power could not be restored led them to delay declaring an emergency with ATC. Once main power had been restored, the crew believed that because they did not require priority for their approach into CYYZ, declaring an emergency was also not necessary.
However, due to the content of the flight crew’s transmissions to ATC, including informing them of complete electrical failure and loss of all navigation, all ATC units treated the flight as an emergency on their own accord, provided priority handling throughout the flight, and instructed emergency vehicles at CYYZ to be on standby.
If flight crews become aware of a situation that may jeopardize safety but do not declare an emergency with ATC, then there is an increased risk that should the situation worsen, the flight will still be airborne due to a lack of priority handling, or that it will land without emergency services standing by.
This article is published under license from Avherald.com. © of text by Avherald.com.
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