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AERO -  Reducing Smoke and Burning Odor Events
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SBO events were analyzed to determine the root cause for each event. Root cause was identified (when possible) down to the component level. Available potential corrective or preventive actions were correlated to the root causes and included in the service letters. Only the top root causes that account for approximately 30 percent of all the reported SBO events are correlated to corrective or preventive action. The results of the studies were provided to operators in service letters that graphically show the predominant root causes (iden­tified by root cause code [RCC] and description), as well as the occurence count of the SBO event (see fig. 2).

Figure 2: Study results for a given airplane model
Root cause codes (RCCs) and operational impacts of SBO events reported for the 757, July 2004 – August 2008.

Minimal Interruption
Cancellation/Out of Service
Air Turnback
Airplane on Ground

RCC 212.001

Recirculation Fan

RCC 790.001

Engine Oil — Over-Servicing

RCC 215.005

Equipment Cooling Fan

RCC 720.001

Engine Fault —
Air Supply Contamination

RCC 561.001

Window Anti-Ice Circuit

RCC 490.001

APU Fault — Air Supply Contamination

RCC 710.001

External Element Ingestion —
Air Supply Contamination

RCC 233.001

Overhead Video Monitor Unit

RCC 243.004

Static Inverter

RCC 253.004

Galley Oven

RCC 215.002

Air Cycle Machine

Number of Occurrences

Because not all SBO events are reported to Boeing, the number of occurrences in figure 2 should be treated on a relative basis. Each root cause is further broken down by an operational impact category, such as delay, diversion, or airplane on ground. Only the predominant root causes are shown in the chart. As a result, not all operational impact categories appear in figure 2. Also, events of undetermined root causes are excluded.


Operators can use the data provided in the associated service letters to initiate action at their discretion to reduce the occurrences of SBO events. The information provided in the service letters is intended for maintenance oper­ations. Flight crew response to in-flight smoke, fire, and fumes is addressed separately in the accompanying article "Flight Crew Response to In-Flight Smoke, Fire, or Fumes."


Most operators would like to locate and stop the cause of the odor, which is often reported as an oil smell or aerosol odor. It can be difficult to identify the odor source, and troubleshooting can result in long airplane downtime and unnecessary engine or auxiliary power unit (APU) changes.

In response, Boeing has developed an oil detection kit that can be used to quickly identify the source of oil leaks or aerosol odors. The kit includes a bleed air sampler and portable infrared spectrometer. Ground crews connect the air sampler to the 3-inch pneumatic ground cart connector and run engine or APU bleed air through the sampler for 10 minutes. The spectrometer and a laptop computer are used to analyze the sample. The kit’s software alerts the user when the sample matches a known contaminant, such as oil or hydraulic fluid.

The oil detection kit works for all Boeing models except the 787 and on all McDonnell-Douglas airplanes. The kit may be ordered online at the Web portal MyBoeingFleet.com by requesting part number J21009.


SBO events can result in expensive operational interruptions. Boeing publishes the most significant root causes for SBO events and correlates these to potential corrective or preventive action in model-specific service letters.

For more information, please contact James Holley at james.a.holley@boeing.com. 

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