August 2012

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Flying through an ash cloud? Here's what Boeing says you should do.

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Boeing Commercial Airplanes, which just officially joined twitter this week, sent out a link today to a 1999 article in Aero magazine, the company's technical journal, about encountering volcanic ash clouds. If you should find yourself inside a volcanic ash cloud, Boeing recommends taking nine steps to getting yourself, your crew and your passengers out of harms way. While you can read the complete article here, I'll went ahead and illustrated the recommendations with photos from a Delta 777-200LR, to give you a sense of the interaction pilots would have in this situation.
Procedures. The following nine procedures are general recommendations. Each operator's flight operations manuals will include more specific directions.

  1. Reduce thrust to idle immediately. By reducing thrust, engines may suffer less buildup of molten debris on turbine blades and hot-section components. Idle thrust allows engines to continue producing electrical power, bleed air for pressurization, and hydraulic power for airplane control.
  2. Turn the autothrottles off. This prevents the engines from increasing thrust above idle. Ash debris in the engine can result in reduced surge margins, and limiting the number of thrust adjustments improves the chances of engine recovery.
  3. Exit the ash cloud as quickly as possible. A 180-deg turn out of the ash cloud using a descending turn is the quickest exit strategy. Many ash clouds extend for hundreds of miles, so assuming that the encounter will end shortly can be false. Climbing out of the ash could result in increased engine debris buildup as the result of increased temperatures. The increased engine buildup can cause total thrust loss.
  4. Turn on engine and wing anti-ice devices and all air-conditioning packs. These actions improve the engine stall margins by increasing the flow of bleed air.
  5. If possible, start the auxiliary power unit (APU). The APU can power systems in the event of a multiple-engine power loss. It can also be used to restart engines through the use of APU bleed air.
  6. If volcanic dust fills the flight deck, the crew may need to use oxygen. Use flight deck oxygen at the 100 percent setting. Manual deployment of the passenger oxygen system is not required because it will deploy automatically if the cabin altitude exceeds 14,000 ft.
  7. Turn on the continuous ignition. Confirm that autostart is on, if available. In the event that the engines flame out or stall, use appropriate procedures to restart the engines. During restart, the engines may take longer than normal to reach idle thrust due to the combined effects of high altitude and volcanic ash ingestion. If an engine fails to start, try restarting it again immediately. Flight crews should remember that the airplane may be out of the airstart envelope if the encounter occurs during cruise.
  8. Monitor engine exhaust gas temperature (EGT). Because of potential engine debris buildup, the EGT can climb excessively. The flight crew should prevent EGT exceedances. Shut down the engine and restart it if the EGT is approaching limits similar to a hung start.
  9. Fly the airplane by monitoring airspeed and pitch attitude. If necessary, follow the procedure for flight with unreliable airspeed.

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