What happened
On 15 January 2009, an Embraer 190-200, registration G-FBEH, was performing a scheduled passenger service from Aberdeen to London Gatwick. While cruising at FL3/70 over Edinburgh, the Senior Cabin Crew Member observed an "ice-blue" colored substance emanating from the forward galley sink. After inspecting the area, the crew found no signs of fire or odor, but the visual appearance of the substance led to concerns regarding a potential fire.
In response to the perceived threat, the flight crew initiated the 'Electrical System Fire or Smoke' procedure. This involved transitioning the aircraft to emergency power by disarming emergency lighting and deploying the Ram Air Turbine (RAT). This transition caused the cabin lighting to extinguish, leaving the cabin in near darkness. During this period, the cabin crew attempted to contact the flight deck via the interphone system but were unable to establish voice communication. The lack of response, combined with the sudden darkness and the loud noise from the RAT, led the cabin crew to fear that the pilots might be incapacitated. They attempted to use the emergency flight deck access system, but were unable to gain entry.
The investigation
The investigation focused on the source of the blue substance and the failure of the communication systems under emergency power. Chemical analysis of the boiler and drip tray from the galley sink showed no evidence of anything other than normal water usage.
Regarding the interphone, investigators found that while the 'PILOT' call button functioned by illuminating a green light in the cabin, the corresponding 'CAB' pushbuttons in the flight deck failed to illuminate, preventing voice contact. It was determined that under emergency power, the interphone system's 'PILOT' function provided a false positive indication of a working connection. Furthermore, the investigation found that the aircraft's flight deck access system relies on manual action from within the flight deck when operating on emergency power, a detail that was not adequately covered in the operator's manuals or crew training.
Findings
- The initial trigger was a visual misinterpretation of water/scale from the galley sink as smoke.
- The transition to emergency power caused a loss of cabin lighting and significant noise from the RAT.
- The interphone system provided a misleading signal that a call had been received in the flight deck when it had not.
- The cabin crew were unable to access the flight deck because the emergency access system requires flight deck intervention when on emergency power.
- There was a lack of specific training and manual guidance regarding system behavior during electrical emergencies.