In the old days when aircraft were made of wood and linnen and men of steel, birds had no problem avoiding these low and slow aircraft. But these days aircraft are fast and make less noise, birds have trouble staying out of the flight path. Certain area's in your country can be designated as bird sanctuaries and flight in such an area involves a higher risk of bird strike. In this article we discuss the effects of a bird strike, as even a small bird can have big consequences for the aircraft and those on board.

Bird Hazards

The pilot has the responsibility to see and avoid. But in the case of birds that could prove difficult. Most bird strikes happen between 50 and 800 feet AGL, although the risk is not zero at higher altitudes.

Piston engined aircraft have an advantage compared to turbine powered types, they make more noise thus warning the birds to get out of the way. Do keep in mind that some high speed piston aircraft do not give the birds time enough to move out of the way. Think Lancair types. Higher speeds lead also to greater impact forces and possibly more serious results.

A collision has enough energy to create a problem for the aircraft, shattering windscreens, tearing open skins, rupturing hydraulic lines, destroying propellers, turbine blades and more.. you get the picture.

Impact Energy

According to Newton, kinetic energy is defined as: E = 1/2 * m * v², with m (mass) in kg, v (velocity) in meters per second and the result in Joules or kgm²/s².

The above was a little technical but we need it to understand why a bird strike can cause so much damage. Lets take a bird of 500 grams and this bird hits an airplane traveling at 90 Kts (46,3 meters per second). The kinetic energy of the impact is 1/2 * 0,5 * 46,3²= 536 Joules. The airplane is thus hit with an force of 536 kgm²/s². And that will make quite a dent...

Doubling the weight of the bird doubles the impact energy, but if the airplane travels twice as fast (180 Kts) the impact is quadrupled! See: E = 1/2 * 0,5 * 92,6² = 2144 Joules.
Flying low gets a whole new meaning here...

The problem

Any type aircraft has been subject to a bird strike, even I had one while on final for a landing and the bird left a very small dent in the strut of the aircraft. Nothing to worry or do about but the impact could be heard with headsets on and engine running.

Bird sight and hearing
Birds have good vision and hearing and they use these senses to warn them for danger. If you have an colorful aircraft (like yellow) then the bird will see it in advance and has time to move out of the way. Interesting point: birds have a problem telling in which direction a turning aircraft is moving so bird strikes seem to occur more when aircraft are changing their flightpath.

Bird behaviour
As aircraft are only part of the birds natural environment for the last 100 years they have not developed the instinct to handle these man made devices. They all react different to an aircraft. Some will do nothing and move out of the way when its absolutely neccessary, onyl to land a few meters ahead. Other will try to outfly the aircraft, turning in the last second to the left or right. And on occasions they will attack the aircraft thinking it is prey they can eat or to defend their chicks.
Personally I was in the situation once that birds gathered on the runway just before take off and I had to commence the take off slowly to give them time to get out of the way. It worked because the runway had sufficient length, but what to do when the runway is a mere 1000 ft..

Bird control measures

Birds are frightened easily, so unnatural sounds like a loud bang does the trick. Natural bird sounds as distress calls work well too. But as birds need to feed too they sort of 'get used' to these sounds and they ignore these so called threats to their safety. Certificated aerodromes are required to take bird control measures. But when they are not, the pilot and aircraft operator are responsible for the safe operation of the flight. And if birds become a hazard at such airports the need to contact the airport manager to control the problem is mandatory.

Avoiding bird strikes
The pilot is responsible to see and avoid. ATC can advise of possible hazards known to them (PIREPs) and the airport operator will also do his/her best. But in the end its the pilot who must avoid them.
First thing he can do is turn on landing lights and strobes. They must be on when operating in reduced visibility conditions. If you fly regularly below 500 ft (crop spraying) you can protect yourself to become familiar bird nesting and feeding area's. Birds are creature of habit and remain territory they inhabit.

Bird strike reporting
Bird strikes cost a lot of money every year, thus it is important that the ATS unit, airport operator and even the CAA knows about them to take measures to avoid these and reduce danger. In some countries a near miss or strike is an incident/occurrence and needs to be reported. Make sure you check your local rules on this.