What makes a bird strike different is that it’s an unpredictable collision. If we talk about aircraft collisions with terrain the outcome is predicable bad. All that kinetic energy must go somewhere. So, a high-speed vehicle hitting something that is immovable is not going to end well.
Now, it must be said that some hunting birds can dive at incredible speeds. More typically, a large bird in flight between feeding sites isn’t going to be traveling fast. In fact, it may as well be viewed as a static object relative to an aircraft in flight. A bird in-flight is unlikely to be able to take avoiding action. For a pilot the action of “see and avoid” may work in respect of other aircraft but a bird ahead is no more than a pinprick in the sky.
These factors make aircraft bird strikes inevitable. That said, the range of outcome because of impacts are rarely at the severe end of the scale. One reason for this is the effort made at design certification to ensure an aircraft is sufficiently robust. Damage can occur but if the aircraft design and test processes have been rigorous everyone should get home safely.
I remember paying particular attention to the zonal analysis done by several major manufacturers. In my experience the most difficult designs are for those of business jets and large helicopters. One of the design challenges in both cases is the limited physical real estate within the aircraft structure. Weight is another big consideration. This leads to cramming essential avionics and electrical systems and their interconnections into confined spaces.
Zonal analysis is about ensuring there’s segregation between different systems. Afterall what’s the point of having two Attitude & Heading Reference Systems (AHRSs)[1] and putting them next to each other in the nose cone of an aircraft. That’s not a good design strategy. One damaging impact must not take out two essential independent aircraft systems.
It’s just as important to ensure an aircraft’s wiring isn’t all bundled togther and taken through one connector. That may save money on electrical parts but it’s not going to work after being hit hard by a 5kg goose.
These issues will need particular care in the new electric vertical take-off and landing (eVTOL) aircraft that are on the drawing boards. Choosing a safe architecture, manufacturers must balance the use of creative design solutions, to produce a competitive product, with limited physical space.
A couple of key words in the certification requirements concern hazards that are anticipated. Bird Strike is hazardous and aircraft systems and equipment must “perform their intended function” should it occur. See EASA Special Condition for small-category VTOL aircraft, Subpart F[2].
POST: Good to see the bird strike criteria Joby’s airworthiness criteria: A blueprint for the nascent eVTOL industry – Vertical Mag
[1] https://helicoptermaintenancemagazine.com/article/layman%E2%80%99s-guide-attitude-heading-reference-systems-ahrs
[2] https://www.easa.europa.eu/sites/default/files/dfu/SC-VTOL-01.pdf
John Vincent 