Bird strikes are an ever-present danger to aircraft. When birds are ingested into jet engines, they can cause severe damage and even engine failure. But modern jet engines are designed to withstand bird strikes to some degree. In this article, we’ll look at whether jet engines can survive bird ingestion and what factors determine the outcome.
What Happens When a Bird Is Ingested Into a Jet Engine?
When a bird flies into a jet engine fan or compressor, several things can happen:
– The bird can be chopped up by the fan blades and pass harmlessly through the engine core. This causes little or no damage.
– The bird can partially block the airflow into the engine, causing the engine to stall or flameout. This requires the engine to be restarted once the obstruction has cleared.
– The bird can break off fan blades, bend compressor blades, or damage other internal components. This can cause an engine surge, vibration, power loss, overheating or other operational issues.
– The bird strike can destroy key components like compressor blades or combustor parts. This usually necessitates a full engine replacement.
The most severe bird ingestion events cause catastrophic secondary damage. For example, broken compressor blades can pierce the engine casing, fuel lines, sensor wiring and other systems. Or liberated blades and disk fragments from the engine can penetrate the aircraft fuselage or fuel tank. These situations can lead to emergencies like uncontained engine failures, fires, or the loss of control of the aircraft.
Key Factors That Determine Bird Strike Outcomes
Several factors influence the extent of damage when a bird is ingested into a jet engine:
Bird Size
Larger birds like geese and gulls are more hazardous than smaller birds. Turkeys, ducks, and pigeons can also severely damage engines. The largest birds exceed the engine inlet size and can shear off fan blades during ingestion.
Bird Density and Quantity
Striking multiple small birds may have the same effect as a single large bird. Ingesting a flock of starlings or sparrows can obstruct airflow and lead to engine failure.
Engine Size
Larger engines on widebody jets are more resistant to bird strikes than smaller engines on narrowbody aircraft. The fan blade width and bypass ratio influence the proportion of bird remains passing into the engine core.
Engine Speed
Bird strikes at low altitudes and speeds close to takeoff are more dangerous. The fan and compressor are spinning faster at high power, increasing the likelihood of damage. Bird remains also have less time to exit the engine during climb.
Engine Location
Ingesting a bird in an underwing podded engine may be safer than a strike on an overwing engine. The fuselage can shield critical aircraft systems from liberated debris.
Modern turbofan engines are most vulnerable during takeoff and landing due to the combination of high thrust demands and greater bird activity at lower altitudes. Fortunately, the industry has made strides in designing more bird strike resistant engines.
Jet Engine Standards for Bird Strike Resistance
Aircraft engine certification requires demonstrating bird strike resistance capabilities without unacceptable failures or collateral damage. For example:
- Transport category jet engines must withstand ingesting a 4-pound bird at cruising speed without an uncontained failure.
- A medium-sized bird strike during takeoff must not prevent a safe landing.
- No more than 25% thrust loss after ingesting a specified number of small birds.
In addition, engines must demonstrate structural integrity after bird strikes without any liberation of high-energy debris outside the engine casing. Manufacturers perform extensive ground-based bird ingestion testing to prove these safety requirements.
Jet Engine Design Features for Bird Strike Resistance
Jet engine technology has evolved to handle bird strikes more effectively:
Wide-Chord Fan Blades
Modern turbofans have increased bypass ratios, with shorter and wider fan blades. This allows birds to be chopped into smaller pieces that are less likely to damage downstream components.
Blade Containment
Fan and compressor blades are designed to shear at the base rather than breaking into fragments during bird ingestion. This contained blade failure is less likely to pierce the engine case.
Blade Shields
Some engines have added titanium shields to prevent liberated fan blade fragments from exiting the engine and damaging the aircraft.
Discardable Spacers
Spacers between compressor blade rows are designed to shear and absorb impacts when birds or debris are ingested. This limits damage to actual compressor blades.
Impact Resistant Composites
Engine components like fan cases and cowlings now use tougher composite materials like carbon fiber. This increases impact and penetration resistance during bird strikes.
Expanded Operating Range
Smart engine control systems and surge bleed capabilities enable engines to maintain operability despite airflow disruptions from bird ingestion.
With better blade and case designs, modern engines can tolerate significantly more bird strike abuse before catastrophic failure occurs.
Notable Jet Engine Bird Strike Incidents
Here are some memorable aviation events involving damaging bird strikes on jet engines:
US Airways Flight 1549 “Miracle on the Hudson” (2009)
An Airbus A320 ingested multiple geese into both engines after takeoff from New York’s LaGuardia Airport. With no engine thrust remaining, the pilots safely ditched the plane on the Hudson River. All 155 people on board survived. The airplane was a write-off.
NASA DC-10 Bird Strike Test (1984)
As part of a bird strike research program, NASA intentionally shot birds into the engines of a retired DC-10 airliner. Birds as large as 4 pounds were hurled into the giant GE CF6 engines at 400 mph. The engines were extensively damaged but contained all debris successfully.
Delta Flight 89 Disaster at Boston Logan Airport (1960)
A Lockheed Electra ingested European starlings during takeoff, causing all four engines to fail. The plane crashed into Boston Harbor, killing 62 people. This accident spurred efforts to limit bird populations around airports.
Ethiopian Airlines Flight 604 (1988)
A Boeing 737 sucked pigeons into its engines during takeoff from Bahir Dar, Ethiopia. An engine caught fire and the plane crashed shortly after takeoff, killing 35 passengers.
Ryanair 737 Emergency Landing in Rome (2008)
Multiple starling strikes at Rome Ciampino Airport caused the number 2 engine to lose power. The crew were able to land the plane safely but the engine was destroyed by internal damage.
These examples underscore the potential perils of bird strikes. Yet engine failures are still relatively rare despite frequent minor bird ingestion. Modern jet engines are robust enough to withstand most bird collisions without catastrophe.
Conclusion
Jet engines are designed to cope with bird strikes to a significant degree. Wide-chord fan blades, blade containment features, and impact-resistant casings provide resilience against bird ingestion. Powerplant standards require engines to tolerate large bird strikes without dangerous uncontained failures. Nonetheless, multiple large bird ingestion under low altitude, high thrust conditions remains extremely hazardous. Aircraft designers continue seeking ways to further improve bird strike survivability and prevention. With sound airport bird management and smart flight planning, the risks can be reduced. But eliminating the danger entirely remains an elusive goal.
