Foreign Object Damage:

The continuing story of US Airways Flight 1549


On Jan.15, 2009, on climb out from KLGA at about 3,200 feet, US Airways Flight 1549 encountered a bit of FOD, or foreign object damage, most likely a flock of migrating Canada Geese. The comment from the cockpit was “Aaah, this is Cactus 1549. We hit birds. We lost thrust in both engines. We’re turning back toward LaGuardia.” The next series of events concluded with the Captain Chesley Burnett Sullenberger III, First Officer Jeffery B. Skiles, and cabin crew Sheila Dail, Doreen Welsh, and Donna Dent making a successful water landing in the Hudson River.

On that January morning the good passengers on Flight 1549 were holding a fist full of aces. They were ever so fortunate to be flying with Captain Sully. I think all of us have thought that if we ever have to ditch, we want Captain Sully to be up front. He is an expert in crew resource management (CRM) and aircraft safety, and a master of the psychology in keeping an airline crew functional during just such events. Captain Sullenberger was a fighter pilot, holds an Airline Transport Pilot Certificate and Commercial Pilot Certificate, and is an expert flight instructor for gliders. This experience was extremely important after the engines stopped, and it became very quiet up front. Captain Sully successfully negotiated the morning rush hour on the Hudson and put the plane down in the ferry route between New York and New Jersey. All 150 passengers and crew were evacuated safely.

That was the happy ending — and now the aircraft and engines are behind closed doors, and forensic detectives continue the technical investigations. Volumes of data will be produced, reviewed, and analyzed before the final NTSB report is written. It will probably be a couple of years before we can read the technical details from this bird strike. However, we can advance the Flight 1549 story a chapter or two with some existing information from the original equipment manufacturers (OEMs), preliminary data from the agencies, and our own knowledge of history.

Aviators and aircraft mechanics have a long and troublesome history with bird strikes. According to his log, on Sept. 7, 1908, Orville Wright’s aircraft hit and killed a bird while flying circles over a field near Dayton, OH. On April 3, 1912, Cal Rodgers, the first person to fly across the country (with Charles Taylor as his mechanic), was flying an exhibition near Long Beach, CA, where it was reported that he struck a seagull, jamming the flight controls. He was killed when his Model EX “Vin Fiz” crashed into the breakers. Data today suggests that the annual cost to the aviation community from bird strikes is upward of $1.2 billion in direct repair cost, as well as lost revenue opportunities to owners and operators. There is no cost that can be assessed to the lives lost from these events.

I was specifically interested in the damage to the engines caused by the bird strikes. Preliminary NTSB forensic evidence on Flight 1549 suggests that the “primary targets” were Canada Geese. Damage from bird strikes begins at the point of impact, usually on the leading edges of the wings and stabilizers, engine nose cones, cowlings, and inlets. Engine ingestion of objects can be catastrophic because of the stacked modular design of the engine, and the energy developed by the rotating mass of the compressors and turbines.

FOD to engines in cases such as bird strikes can trigger succession damage, leading to tiny nicks on the front edges of the fan blades, to full-scale destruction of the compressor and turbine section. Usually when the FOD strikes fan blades, the blades distort and cause tip scrub and curling, as well as the loss of material from the casing. This abrasion can continue into the low pressure compressor, resulting in more damage and debris that can affect the leading edges of the high-pressure compressor blades and vanes. If the damage is great enough to disrupt airflow, the engine loses thrust or may seize completely. Aircraft are likely to incur the most damage during takeoff and climb out when power settings are high, the plane is at a low altitude, and crews have little time and room to maneuver.

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