Attrition: Organic But Unpredictable Anti-Aircraft Systems

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January 23, 2016: An increasingly common problem for commercial and military aircraft is bird strikes. This is especially true of Africa where there are larger populations of birds and small land animals. Military air bases, which tend to be in remote areas, are even more exposed to the possibility of bird strikes or animals unexpectedly moving onto air strips. There have been some clever solutions to this problem. The South African Air Force has developed a unique and effective cure for this hazard; cheetahs. These small (28-65 kg/62-143 pounds for adult males) animals normally avoid humans and prefer smaller game. Actually, cheetahs are the most easily domesticated (for hunting or pets) of the big cats and that has been done for thousands of years, especially in Africa (ancient Egypt left lots of records on this).

Since the 1990s the South African Air Force has been using cheetahs to keep birds and small animals away from military air fields. South Africa has a large wild population of cheetahs as well as a domestic breeding program to keep the wild population viable. The widespread introduction of firearms in rural South Africa in the 20th century meant a lot more big cats, including cheetahs, were killed by expanding human populations. But the cheetahs raised in the breeding programs are comfortable enough around humans to be released onto military air bases so they can hunt (and chase away) large concentrations of birds or small animals who are, if left alone, are a major threat to aircraft landing or taking off. Young male cheetahs are used, because in the wild they will hunt together while the females are generally solitary. Air fields get a new pair of young males evert two years. Equipped with GPS locator collars (in case they are injured or, rarely, run off) these cats serve for two years before being returned to the breeding program and eventually the wild. Very rarely one of these cheetahs will injure a human, usually because they feel threatened. On military bases all personnel are instructed on how important it is to leave the big cats alone if they wander (usually out of curiosity) into work or housing areas.

The cheetahs also chase some of the birds away from airfields as wild cheetahs find birds tasty, if difficult to catch prey. Aircraft bird strikes are a widespread, if little publicized, problem for all airports. There are about 5,000 incidents a year. These often just mean replacing windows or canopies, or wherever the bird hit. Most of the incidents involve near misses or collisions on non-critical portions of the aircraft. But in about one percent of the incidents the damage is severe and some aircraft are lost. On average, 40-50 people a year die because of aircraft bird strikes.

Nearly all the fatal bird strikes are to aircraft with gas turbine engines (which birds fly into). This often wrecks, or severely damages, the engine when the high speed fan is damaged. Multiple engine aircraft usually can survive this if they still have one or more working engines. But sometimes single or two engine aircraft lose all engine power and go down with heavy loss. One exception was the "Miracle On The Hudson" in January 2009, when Airbus 320 over New York City lost both engines to bird strikes. Exceptional work by the crew managed to bring the aircraft down, intact, on the Hudson River. Hail caused a similar (although not as life-threatening) incident in 2006, where a B-727 jet was climbing after takeoff from Calgary (in central Canada) when it ran into a massive hail storm that did extensive (but not disabling) damage to the aircraft exterior. With most of the lights out and the cockpit windows obscured by cracks caused by numerous fast moving hail stones, the aircraft turned around and landed safely.

In rare cases these can even bring down a helicopter. For example, in 2011 a U.S. Marine Corps collided with a red-tailed hawk, weighing about 1.4 kg (3 pounds). The bird hit the top of the main rotor mast on a marine AH-1W helicopter gunship. The hawk impact damaged the pitch change link, which caused vibrations that quickly led to the transmission and rotor blades breaking away from the helicopter. The chopper then fell to earth, killing the two man crew. The AH-1 has since been modified to better protect the pitch change link, one of several highly vulnerable (to damage) components on a helicopter. Normally, the pitch change link would not be hit by ground fire. No one thought the risk of a bird strike up there was worth doing anything about.

 


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