# What is “Bird Strike Speed”?

I read through the reference speeds of the Hawker 850XP and I stumbled upon the "Bird Strike Speed". It is specified as "280 KIAS up to 8000 ft".

• What does that speed mean?
• LOL. Maybe its like turbulence penetration speed, its the best speed at which to penetrate a flock of birds? Apparently the speed is different in cold weather. – Devil07 Aug 9 '17 at 13:14
• @Devil07 Yes, in cold weather you have to worry about hitting frozen chickens -- they're harder on the windshields, as the Mythbusters finally figured out (on the 3rd try!). – Ralph J Aug 9 '17 at 20:16

Aircraft structures are required to withstand the structural damage caused by birdstrike. According to 14 CFR 25.571 - Damage - tolerance and fatigue evaluation of structure:

(e)Damage-tolerance (discrete source) evaluation. The airplane must be capable of successfully completing a flight during which likely structural damage occurs as a result of -

(1) Impact with a 4-pound bird when the velocity of the airplane relative to the bird along the airplane's flight path is equal to Vc at sea level or 0.85Vc at 8,000 feet, whichever is more critical;

In case of aircraft with high cruise speed, the speed may be limited below 8000 ft to comply with this regulation. As Bird Strike Requirements for Transport Category Airplanes notes,

... to meet current bird strike criteria, some manufacturers specify relatively low $V_{MO}$ and $V_{C}$ airspeeds up to 8000 feet, that increase above that altitude.

The 'bird strike speed' is likely this.

• What about a 20 pound Canada Goose? – Devil07 Aug 9 '17 at 18:10
• @Devil07. Assuming the limit is a kinetic energy limit, KE=1/2 m v^2, so if m goes up from 4 to 20 pounds, v^2 needs to reduce by 5, hence I say 125 KIAS for your goose (unfrozen). – Penguin Aug 10 '17 at 3:38