What happened
On 15 January 2009, an Embraer 190-200, registration G-FBEH, was operating a scheduled passenger flight from Aberdeen to London Gatwick. While cruising at FL370 over Edinburgh, the Senior Cabin Crew Member observed an ice-blue coloured substance, resembling smoke, emerging from the forward galley sink. Following emergency protocols, the flight crew transitioned the aircraft to emergency power by deploying the Ram Air Turbine (RAT) and disconnecting the engine-driven generators.
This transition caused the cabin lighting to extinguish and resulted in a loud noise from the RAT operation. During this period, the cabin crew attempted to contact the flight deck using the interphone system. Although the 'PILOT' call button illuminated, the flight crew did not respond, and no voice communication could be established. Furthermore, the emergency flight deck access system failed to function under emergency power. The cabin crew, fearing the pilots might be incapacitated, remained concerned until the commander made a public announcement regarding a diversion to Newcastle.
The investigation
The AAIB examined the aircraft's electrical and communication systems. The investigation established that while the initial 'smoke' was likely steam from a water jug, the subsequent loss of communication was due to the specific way the interphone system operates under emergency power. On emergency power, the 'PILOT' call function provides a visual indication in the cabin but does not illuminate the corresponding 'CAB' button in the flight deck, preventing voice contact. Additionally, the investigation found that the emergency flight deck access system relies on flight deck-side actions when the aircraft is powered by the RAT and batteries.
Findings
- The smoke seen in the galley was likely steam from hot water.
- Deficiencies in the interphone system during emergency power usage prevented the cabin crew from contacting the pilots.
- The 'PILOT' call indication provided a false sense of successful connection to the cabin crew.
- The cabin crew were unaware that the emergency flight deck access system would not function under emergency power.
- The operator's manual and training did not adequately cover system behavior during emergency electrical configurations.