Risk Mitigation- Bird Hazards
Misconceptions about Bird Hazards.
There are some Common misconceptions about bird strikes which may give pilots a false sense of security and prevent them from reacting appropriately to the threat of a bird strike or an actual event are as follows:-
(a) Birds don’t fly at night, in poor visibility, such as in clouds, fog, rain, or snow.
(b) Birds can detect airplane landing lights, weather radar and avoid the airplane.
(c) Airplane colours and jet engine spinner markings help to repel birds.
(d) Birds seek to avoid airplanes because of aerodynamic and engine noise.
(e) Birds dive to avoid an approaching airplane.
None of the above misconceptions have any scientific data to back them.
Detecting a Bird Strike While in Flight
Visual: Birds seen in close proximity to the airplane or colliding with the airplane, bird remains on windshield, cracked windshield.
Tactile: Vibration of airframe or engine, thrust loss, asymmetric thrust, increased drag, abnormal airplane handling characteristics.
Auditory: Noise of strike or noise attributed to resulting damage: engine surging,
Compressor stalls, aerodynamic noise from damaged radome, loss of pressurization
from pressure vessel penetration.
Olfactory: Smoke, odour, or cooked bird smell.
Engine Indications: Reduction or fluctuation in primary power parameters
(e.g., engine pressure ratio, fan speed, or equivalent), abnormal fuel flow, abnormal
engine vibration monitoring (e.g., error vector magnitude or equivalent),
engine failure, engine exceedances.
Flight Instruments: Loss of data or erroneous indications arising from damage to air
data sensors or angle of attack sensors.
Other Airplane Systems or Structure Affected Directly by a Strike: Damaged communications or navigation antennas, damage to exposed electrical wiring or hydraulic lines, damaged radome or weather radar, broken landing lights, or cascading and multiple effects from sensor damage or engine damage.
The following information provides guidance on managing the risk of bird strikes on aircraft and is for guidance only. It does not supersede any regulatory, manufacturer or aircraft operator policies or procedures.
- The speed of the aircraft at the time of bird hit, is the prime determining factor in level of damage resulting from a collision.20% increase in speed results in a 44% increase in impact force.
- Velocity can refer either to the speed of the aircraft or the rotational speed of the Engine.
- Higher the speed, the more likely, the impact will be damaging.
- Encounters with flocking birds, particularly large flocking birds, are very hazardous.
- Modern jet engines and turboprop blades have technological limits which can be exceeded by impact with birds and other wildlife
- Airframe parts, such as windshields, radomes, slats, empennage, etc., are also vulnerable to bird and wildlife strikes.
- Aircraft and engine certification standards do not adequately consider the cumulative effect of simultaneous damage to the aircraft structure, systems and multiple engines which may result from a flock encounter.
- Be aware that migratory bird seasons, species, flight routes and altitude are very location specific.
- The level of risk from migratory birds may vary widely between your departure airport and destination airport and may cause conflicts with your flight planned route.
- Review NOTAMS, airport briefing notes and the AIP for bird/wildlife warnings for your departure and arrival airports as well as climb and descent routes.
- The Pilots need to be Situationally Aware at all times about the potential bird hazards at different airports, seasons and altitudes. The Bird Strike SOP’s should be followed meticulously.
- It is essential to discuss bird strikes during take-off and approach briefings when operating at airports with known or suspected bird activity.
- Be extremely vigilant if birds are reported on final approach.
- If birds are expected on final approach, plan additional landing distance requirement to account for the possibility of no thrust reverser use if a bird strike occurs.
Responses to a Known or Suspected Bird Strike.
- Fly the airplane and maintain flight path control.
- Monitor flight and engine/ multiple engine failure or thrust loss.
- Attempt to restart engine(s) if situation permits.
- Severe Engine Damage– Shut down engine according to procedure.
- Strong Engine Vibration -Reduce thrust, which will often reduce vibration. Shut down engine as per flight crew operations manuals guidance.
- Multiple Engine Ingestion and Abnormal Engine Indications-Return to departure base or divert to nearest suitable airport.
- Known or Suspected Multiple Engine Ingestion, with Normal Engine Indications-Return to departure base or divert to nearest suitable airport.Re-evaluate decision to continue with extended range twin-engine operational performance standards, extended range operations, or overwater flight because engine damage or performance degradation may manifest later in the flight.
- Known or Suspected Strikes with Large Flocking Birds –Return to departure base or divert to nearest suitable airport since damage may affect aerodynamic lift and drag, subsequent fuel consumption and ability to complete the flight, safely.
- Known or Suspected Airframe Damage or Engine Damage.Maintain or reduce speed, do not accelerate unless necessary for safety of flight or to maintain flight path control.
- Damaged Windshield or Depressurization. Below 10,000 feet, discontinue climb and level off. Above 10,000 feet, descend to 10,000 feet or the minimum safe altitude.
- Known or Suspected Strike with Landing Gear Extended or in Take-off or Landing Configuration with High Lift Deployed-Use available system information to assess possible damage to flight controls and high lift devices, and make minimal and prudent changes in airplane configuration in accordance with the flight phase. Use available system information to assess possible damage to landing gear and associated systems, including exposed electrical, pneumatic, and hydraulic systems, and potential effects on the ability to steer and stop on the runway.
- Known or Suspected Strikes to Air Data and AngleofAttack Sensors-Be aware that this may affect other airplane systems and have cascading effects. Be aware of the potential for loss or erroneous air data and degraded flight control modes, including loss of envelope protection or limiting, unreliable airspeed, propulsion systems in alternate mode.
Taxi & Takeoff
- If birds or other wildlife are noted on or near the runway or departure path –either use another runway not affected by the birds or delay takeoff until the birds have been dispersed by airport personnel.
- Use of the aircraft’s weather radar does not have any effect upon birds – they do not hear in the X-‐band frequency and the radar power output is too low
- Birds do not regard aircraft on a runway, either with or without illuminated lights, or the spooling of a jet engine, as a threat.
- They will be unlikely to move until you start your takeoff roll which will, in most cases, be too late to avoid collision
- If a bird strike occurs during the takeoff roll the decision to continue or abort the takeoff should be based upon your SOP and aircraft’s flight manual aborted takeoff criteria.
- If departing from an airport with known bird problems or reported bird problems, climbing on the ICAO Noise Abatement Departure Profile 1 will minimize the time and reduce the distance traveled to reach 3,000’ AGL; 95% of bird strikes occur below 3,000’.
- Birds tend to turn away or dive when confronted with an aircraft. If encountering birds, pull up. This strategy will cause you to pass over the birds, reduce your speed to minimize impact damage and limit flight at lower, bird rich, altitudes
- Encounters with flocking birds can result in damage that affects multiple systems which may include engine/engines power loss, flight instrument/flight computer malfunction due to Pitot tube damage, windshield damage, nose wheel steering loss, penetration of fuselage and flap/slat damage.
- Be aware that engine damage from bird ingestion can be difficult to detect with aircraft instrumentation alone.
- After a bird strike, carefully evaluate, the condition of your aircraft and engines prior to deciding to continue your flight.
- A return for precautionary inspection may be in order.
- If operating in an area of known bird activity, use safe operating speeds during climb.
- Slower aircraft speeds will reduce impact force and the probability of damage in a collision.
- Below 10,000’ do not exceed 250 KIAS or minimum clean speed, whichever is greater.
Descent, Approach and Landing
- If operating in an area of known bird activity, slow down.
- Slowing the aircraft will reduce the impact force and probability of damage in a collision.
- Below 10,000’ do not exceed 250 KIAS or minimum clean speed, whichever is greater.
- If landing at an airport with known bird problems try to remain at or above 3,000’ AGL until necessary to descend on the normal 3° descent profile for landing.
- If birds are reported on or near your landing runway request a different runway not affected by the birds or delay landing until the birds are dispersed by airport personnel.
- At approach thrust settings ingested birds may bypass the engine core via the fan, reducing the likelihood of serious damage
- If birds are encountered at approach thrust settings and landing can be made with that thrust setting, continue through the flock and complete the landing.
- A go-‐around attempt (high engine rpm) which enters the flock is more likely to result in serious engine damage and loss of thrust.
- Be ready to transition to instrument flight if windshields become obscured.
- Upon landing after a bird strike, minimize the use of reverse thrust to lower the risk of engine damage caused by bird ingestion.
- Maintenance protocols should be in place to inspect engines and airframes after a bird strike.
- If a bird strike is suspected ensure a maintenance logbook entry is made describing the event in detail.
- If wildlife hazards are encountered ensure the appropriate safety and/or bird strike report is completed and submitted.
- The collection and analysis of data from bird strike reports is a critical tool to identify and correct problems.
Bird Hits- Helicopters.
Helicopters are more susceptible to bird strikes since most of the helicopter operations are conducted at low altitudes below 3000 ft. However, better forward visibility and slow speeds of helicopters help the pilots in detecting and avoiding birds in time. However, if the pilots are not situationally aware and vigilant while flying in areas and altitudes of known bird activity, a bird hit may occur leading to serious damage to the helicopter. Bird hits may cause serious damage to Main Rotor, Tail Rotor, Engines, control surfaces and the Windshield. In some of the bird hits on the Windshield, the pilots have been blinded due to the bird remains hitting the pilots face with consequent incapacitation. Most of the helicopter crashes after suffering a bird strike have been due to panic reaction or incapacitation of the pilots. The recommended immediate action in case of bird hit by the Helicopter Pilots is not to panic, reduce speed in case of vibrations, fly the helicopter and land at any suitable site or nearest helipad or airport, assess the damage and report the incident.
Bird Strike is common and can be a significant threat to aircraft safety. For smaller aircraft, and helicopters, significant damage may be caused to the structure and all aircraft, helicopters especially jet-engine ones, are vulnerable to the loss of thrust which can follow the ingestion of birds into engine air intakes. This has resulted in a number of fatal accidents.
Bird strikes may occur during any phase of flight but are most likely during the take-off, initial climb, approach and landing phases due to the greater numbers of birds in flight at lower levels. Since most birds fly mainly during the day, most bird strikes occur in daylight hours. However, bird strikes during night have also been reported.
Pilots should not rely on on-board weather radar, landing lights, airplane markings, time of day, or visibility to prevent bird strikes.
Flight operations may need to be modified in the presence of known or anticipated bird activity. Delay take-off or landing in the presence of bird activity. Below 10,000 feet, keep speed below 250 knots if operationally possible. Below 2,000 feet, climb at the maximum rate to reduce the flight time exposure to a strike hazard. Descend with idle power and avoid extended low altitude level flight, particularly over water courses, nature reserves, or other areas of known or expected bird activity.
Although it is not possible to avoid all bird strikes, flight crews can take steps to reduce the chance of a bird strike event. If a bird strike does occur, the appropriate action can improve the flight crew’s ability to maintain control of the airplane and land safely. Sound knowledge, better situational awareness, adherence to the SOP’s, Operational Guidelines and alertness particularly during flight in known areas, seasons or airports of heavy bird activity will keep the bird related incident /accidents to the aircraft ,helicopters, to the minimum.
Flight crews and maintenance and line personnel should be encouraged to report all bird strikes because data are essential to quantify and manage the hazard. Reporting bird strikes enables aviation authorities to monitor the risk to aviation and the effectiveness of wildlife hazard mitigation measures.