|Title:||Smoke emergency over North Atlantic, Boeing 747-436, G-BNLL, 13 April 1996|
|Micro summary:||This Boeing 747-436 experienced a smoke emergency over the North Atlantic.|
|Event Time:||1996-04-13 at 1200 UTC|
|Publishing Agency:||Aircraft Accident Investigation Board (AAIB)|
|Publishing Country:||United Kingdom|
|Diversion Airport:||London Heathrow Airport, London, England|
|Site of event:||2.5 hours into London to San Francisco flight|
|Departure:||London Heathrow Airport, London, England, United Kingdom|
|Destination:||Seattle-Tacoma International Airport, Seattle, Washington, USA|
|Airplane Type(s):||Boeing 747-436|
|Type of flight:||Revenue|
|Diverted to:||London Heathrow Airport, London, England|
|Executive Summary:||Approximately 2.5 hours into a flight from London to San Francisco, the flight deck filled with "hazy, acrid fumes". The 'Smoke Air Conditioning Drill' was carried out, which included the donning of flight deck oxygen masks and switching off the flight deck humidifier. However, although the fumes did not intensify, the smell remained. Accordingly, the decision was made to return to Heathrow where an uneventful landing was made. |
Subsequent investigation confirmed that the flight deck humidifier unit smelt strongly of burned insulation. This unit is connected to the aircraft potable water system, and generates an atomised water spray which is introduced into the flight deck air conditioning ducts. The spray is produced by a rotating, vaned disc, which is driven by a three-phase, 115 volts AC motor. Water is drawn,via an aspiration tube, from a chamber at the base of the unit.
Before disassembly, the unit was run on a test bench, where it was found to be very noisy in operation. After stripping, it was found that the motor bearings were dry and badly worn, although they had not in fact failed. A small amount of rubbing had occurred on the rotor as a result of the worn bearings, and there was evidence of intense heat around the motor, with areas of charred insulation.The vaned disc was encrusted with heavy limescale deposits, which conceivably could have caused out-of-balance forces that contributed to bearing wear. It was also noted that additional limescale deposits had almost completely blocked the aspiration tube, thereby significantly reducing the effectiveness of the humidifier.
The records indicated that the unit had been fitted to the aircraft about 11 months earlier, and had achieved more than 4,700 flyinghours.
|Learning Keywords:||Operations - Cabin or Cockpit Smoke|
|Operations - Maintenance|
|Other - Manufacturing Issues|
|Close match:||Engine failure and evacuation, Airbus A319, November 2, 2001|
|In-Flight Fire Leading to Collision with Water, Swissair Transport Limited, McDonnell Douglas MD-11 HB-IWF Peggy's Cove, Nova Scotia 5 nm SW, 2 September 1998|
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