Engine Thrust Hazards in the
The high levels of thrust generated by today's commercial engines provide for safe takeoff, flight, and landing over a wide range of temperatures, altitudes, gross weights, and payload conditions. However, the exhaust wake from these engines can pose hazards in commercial airport environments. Operators must carefully consider these hazards and the resulting potential for injury to people and damage to or caused by baggage carts, service vehicles, airport infrastructure, and other airplanes.
Power hazard areas
When modern jet engines are operated at rated thrust levels, the exhaust wake can exceed 375 mi/h (325 kn or 603 km/h) immediately aft of the engine exhaust nozzle. This exhaust flow field extends aft in a rapidly expanding cone, with portions of the flow field contacting and extending aft along the pavement surface. Exhaust velocity components are attenuated with increasing distance from the engine exhaust nozzle. However, an airflow of 300 mph (260 kn or 483 km/h) can still be present at the empennage, and significant people and equipment hazards will persist hundreds of feet beyond this area. At full power, the exhaust wake speed can typically be 150 mph (130 kn or 240 km/h) at 200 feet (61 m) beyond the airplane and 50 to 100 mph (43 to 88 kn or 80 to 161 km/h) well beyond this point.
One approach to relating these values to airport operations is to consider the hurricane intensity scale used by the U.S. National Oceanic and Atmospheric Administration. A Category 1 hurricane has sustained winds of 74 to 95 mph (64 to 82 kn or 119 to 153 km/h). At these velocities, minimal damage to stationary building structures would be anticipated, but more damage to unanchored mobile homes and utility structures would be expected. An idling airplane can produce a compact version of a Category 3 hurricane, introducing an engine wake approaching 120 mi/h (104 kn or 192 km/h) with temperatures of 100 F (38 C). This wake velocity can increase two or three times as the throttles are advanced and the airplane begins to taxi.
At the extreme end of the intensity scale is a Category 5 hurricane, with winds greater than 155 mph (135 kn or 249 km/h). Residential and industrial structures would experience roof failure, with lower strength structures experiencing complete collapse. Mobile homes, utility buildings, and utilities would be extensively damaged or destroyed, as would trees, shrubs, and landscaping. At rated thrust levels, a jet engine wake can easily exceed the sustained winds associated with a Category 5 hurricane.
High engine thrust during maintenance activities can cause considerable damage to airplanes and other elements in the airport environment. An example of this problem occurred after an airplane arrived at its final destination with a log entry indicating the flight crew had experienced anomalous engine operation. Subsequent evaluation resulted in replacement of an engine control component, followed by an engine test and trim run to verify proper engine operation. The airplane was positioned on an asphalt pad adjacent to a taxiway, with the paved surface extending from the wingtips aft to the empennage. During the high-power portion of the test run, a 20- by 20-foot (6.1- by 6.1-m) piece of the asphalt immediately aft of the engine detached and was lifted from the pad surface. This 4-inch (10.2-cm)-thick piece of asphalt drifted up and into the core area of the left engine exhaust wake, where it shattered into numerous smaller pieces. The pieces were driven aft at substantial velocity, striking the aft fuselage and left outboard portion of the horizontal tail. The maintenance crew was alerted to the ramp disintegration and terminated the engine run. Subsequent inspection found that the outboard 4 feet (1.2 m) of the left horizontal stabilizer was missing, as was the entire left elevator. Corrective action included replacing the stabilizer and left elevator and repairing holes in the fuselage.
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