Rotana E145 near Al Ain on Sep 12th 2015, PFD1, MFD1 and EICAS went blank, electrical odour in cockpit
Last Update: November 17, 2016 / 17:52:25 GMT/Zulu time
The United Arab Emirates GCAA released their Final Summary Report concluding the probable causes of the incident were:
The Air Accident Investigation Sector determines that the cause of the No.1 IC-600 failure was the overheating of the power supply printed board assembly (PBA). It is most likely that an internal breakdown of the transformer (T1) caused a short circuit resulting in heat buildup on the PBA. The Investigation could not determine why the transformer (T1) had broken down.
The heat caused the power supply board to disconnect the No.1 IC-600 resulting in PFD1, MFD1, and EICAS displays going blank with a red (X), and the autopilot to automatically disengage.
The GCAA reported the aircraft had accumulated 23,321 flight hours in 21,727 flight cycles.
The GCAA complained that the GCAA learned of the occurrence only through a routine review of the mandatory reporting system delaying the notification by 4 days. By that time the aircraft had already performed several more flights, both cockpit voice and flight data recorders had been overwritten.
The failed primary integrated computer IC-600 was removed from the aircraft and exhibited an odour of burning, its power supply showed thermal damage to the power supply. The IC-600 was sent to the manufacturer for further tests. A component of the power supply was found severly charred to a point, where testing and determination of the cause of the failure was not possible. The manufacturer however concluded based on previous experiences, that the internal transformer T1 had created a short circuit which resulted in a heat build up.
The GCAA analysed:
The failure of No.1 IC-600, caused the PFD, MFD, and EICAS displays go blank, stop displaying data, and to display a red (X). In addition, the failure of No.1 IC-600, being the data processor for the autopilot, lead to autopilot disengagement.
During the Incident flight, when the Commander, who was the PM, pushed the SG button on the No.1 reversionary panel, the display units were recovered.
Since the autopilot functions are only linked to the No.1 IC-600, the autopilot disconnected after the No.1 IC-600 failure. The AUTOPILOT FAIL message appeared on the EICAS and the autopilot could not be re-engaged.
According to the design, if a flight director fails, an FD FAIL message is displayed on the lateral mode annunciator box, and the flight director mode annunciators, and the command cues are removed. The failure of the flight director causes the autopilot to disconnect automatically.
The Investigation did not discuss the sequence of GPWS malfunction messages during descent, and whether that happened before the Commander, as he stated, isolated the AC power during the descent or as a consequence of that.
The Aircraft’s AOM and QRH contained emergency/abnormal procedures related to failures of the displays, autopilot, and the IC-600 (appendix 1).
In the sequence of steps, the IC Failure/IC Bus Failure checklist ends with the crew pushing the corresponding SG on the reversionary panel. The Autopilot Failure checklist ends by disengaging the autopilot.
The differences between the emergency/abnormal procedures and checklists in the AOM and QRH in some topics may cause confusion to the crew and may indicate that part of the procedures are not as up to date as the other part.
For instance, missing the ‘odor condition’ in the QRH’s Electrical System Fire or Smoke checklist can prevent the crew from implementing the checklist in case of odor only.
The lack of an explicit precautionary note about autopilot loss in the case of a No.1 IC-600 failure does not help in preparing the crew mindset for changing the flight from AFCS to manual.
Mentioning in the AOM that the autopilot disconnection aural warning will activate only below 2,500 ft radio altitude, whereas this condition was not mentioned in the QRH, provides vague information to the crew.
The Investigation believes that the discrepancies in the checklists and procedures may add unnecessary workload to the crew in emergency/abnormal situations that require straightforward procedures leading to the recovery of safe conditions.
Crew Performance and Emergency Handling
The crewmembers experience and initial training assisted them in identifying that the cause of disappearance of the PFD, MFD and EICAS data from the screens, and the appearance of the red (X), was the failure of the No.1 IC-600. The Commander, who was the PM, pressed the SG button located on the No.1 reversionary panel in order to switch to the No.2 IC-600. The IC BUS FAIL caution displayed on the EICAS, and the screens were recovered.
The odor sensed later was diagnosed by the crew to be electrical, and both crewmembers believed that the source was the No.1 IC-600 based on the displayed data having been replaced by red (X) marks.
The crew initiated the Electrical System Fire or Smoke checklist and both crewmembers donned their emergency oxygen masks.
When the TERR INOP and GPWS INOP messages appeared on the EICAS, the Commander pushed the AC power button to isolate the affected systems and decided to divert to Al Ain Airport, UAE, due to high terrain near Muscat Airport. This was appropriate action to mitigate the risk of flying above high terrain with a deactivated GPWS.
The crew practiced good crew resource management (CRM) with the copilot manually controlling the Aircraft. The cockpit-cabin communication was managed appropriately and the safety information was exchanged in a timely and accurate manner.
The Commander provided a NITS briefing for a precautionary landing since he believed that the situation did not require evacuation unless smoke developed, in which case he would declare an evacuation. The Commander was the flight crewmember who maintained communication with the cabin since he was the PM.
During the descent to Al Ain Airport, the applicable checklists were actioned normally.
This article is published under license from Avherald.com. © of text by Avherald.com.
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