# Why don't jetliners maneuver to avoid a bird strike if spotted in time?

With 75%* of the bird strikes hitting the wings and engines, why isn't there any training to avoid such strikes by banking if a flock was spotted with enough time to react?

It seems what Boeing recommends* is to ride it out then assess the damage.

Avoid or minimize maneuvering at low altitude to avoid birds.

(...)

Fly the airplane and maintain flight path control.

In the Flying Wild Alaska TV show one time the pilot of a light plane supposedly (exact clearance not shown) banked to avoid the birds. (YouTube)

Is there a correct banking maneuver? Suppose the flock is heading for the right wing, here's what I think of the two alternatives:

1. Dip the right wing to move the upwash away from the flock's path, or
2. Raise the right wing because birds are better divers than climbers.

In US Airways 1549 both engines suffered, and I don't know if dipping one wing or the other could have saved one engine. According to the CVR transcript, from announcing "birds" to the strike there was a full second. With a typical human reaction time of 0.3 seconds to announce birds, there would have still been a complete second to roll the plane one way or the other. Enough to roll 15° in an Airbus (max normal law FBW roll rate is 15°/s).

Why is riding it out better than a bank? (Worst outcome is the same for doing nothing and doing something.)

I'm neither claiming a solution, nor discussing flight 1549 in particular, rather inquiring about the flaws in my understanding of bird strikes and the related avoidance maneuvers.

• That would be nice, second best thing would be any studies on avian behavior when faced with flying metal if you know any.
– ymb1
Sep 26 '18 at 19:28
• The short answer, whether flying a small or large aircraft, is that birds are better at maneuvering than you are. Sep 26 '18 at 20:06
• A single bird should not cause a disaster. Even the worst case of flying with one engine out is a standard drill that trainee pilots learn as soon as they progress to multi-engine aircraft, not an unknown emergency situation. But if you encounter a flock of birds (like the 1549 situation) the chances of avoiding the whole flock are negligible - therefore, don't bother to try. Sep 27 '18 at 0:24
• Note that 1 second is only enough time to roll 15° if you are already rolling at 15°/s. Roll acceleration is limited, and with a fairly generous figure of 10°/s^2, one could only roll 5° in one second starting from zero roll rate - and that is assuming the pilots instantly determining the appropriate control input to make, and the control surfaces reacting instantly to the pilot's input. Sep 27 '18 at 9:03
• @ymb1 , as everyone has said, you've just massively, spectacularly, overestimated how much time is involved! Bird strikes are "instant". A perfect analogy is, could you "dodge" an insect hitting your windscreen while driving a car - the answer is "of course not!" Sep 27 '18 at 14:04

# Not possible to see birds in time

Incredible as it may seem, this re-enactment of flight 1549's bird strike is actually drawn out and made twice as long as it actually happened.

The Cockpit Voice Recorder transcript, note the seconds.

15:27:10.4 HOT-1 birds.

15:27:11 HOT-2 whoa.

15:27:11.4 CAM [sound of thump/thud(s) followed by shuddering sound]

15:27:12 HOT-2 oh shit.

15:27:13 HOT-1 oh yeah.

15:27:13 CAM [sound similar to decrease in engine noise/frequency begins]

15:27:14 HOT-2 uh oh.

15:27:15 HOT-1 we got one rol- both of 'em rolling back.

1.0 seconds from calling out "birds" until the engines were ingesting them, 4.6 seconds to calling out that the engines are rolling back. That is how fast it happens.

Flight 1549 was travelling at between 210 and 220 knots when the collision happened. That is little over 100 meters per second. Unless you are looking directly at a Canada Goose (which is the kind of birds 1549 collided with), you cannot even see the bird beyond 1 km away. So in the very best of circumstances, you have less than 10 seconds to react. But if you are heading directly for the bird, then you are subject to the "blossom effect" and not very likely to notice the bird until 1-4 seconds before impact, because the eye simply cannot see something that small when travelling towards it at those speeds.

By another example... can you notice the plane in time?

So there is no training to dodge birds, because if you are so close you can see the birds then it is already too late and there are no manoeuvres you can perform that will remedy the situation. Instead you risk exacerbating it by losing the engines and losing control at the same time.

Training focuses on not being where birds are likely to be.

• OMG that video... I was like, how could you not spot the giant airlin.... OH GOD!!!
– Jamiec
Sep 27 '18 at 10:10
• @Jamiec Clever, isn't it. :D The video gets the point across very effectively in my opinion. Sep 27 '18 at 10:15
• It does indeed. The about of times I've been flying and spotted traffic and become a bit fixated by it, but therefore forgetting to keep scanning for other traffic. I learnt an important lesson today.
– Jamiec
Sep 27 '18 at 11:44
• Great answer. Ever hit a bird while driving a car? I have. I was probably going 60 mph or so. Not a snowball's chance of seeing it in time, and that's a much lower speed. Another example - my aunt saw a raccoon while driving, tried to dodge it, went off the road, where her car entered a ditch and flipped over. Just hit the bird. Sep 27 '18 at 22:03
• @Jamiec while you're at it, do the same with trains. You watch the tail of the freight train go by with its flashing rear marker and go "yay" and start across, except the train obscured the view of another train bearing down on the crossing on the next track. Sep 28 '18 at 1:48

If you're low, slow, and heavy (say, early in climb with full passenger and fuel load for a transcontinental or transoceanic leg), just dipping a wing can result in a stall and crash if you lose power while in a more than minimal bank.

The reasoning goes like this: the birds might not hit you. If they do, it's unlikely you'll lose all engine power. Even if you do lose all power, if the aircraft is level wings and not maneuvering, you have the most options for a safe landing (return to port, land on a nearby strip, land on flat ground or a road, etc.).

A sharp maneuver at that stage of a flight can itself cause a crash, never mind what will happen if you get a bird strike anyway.

• This may be science fiction, but is there any kind of shield in existence that can be deployed to aircraft? Like, some sort of fast acting iris that will close in front of the engine intakes when birds are sighted? Or would creating an obstruction to airflow in front of the engines like that be just as dangerous as the birds entering the engine? What do war aircraft do to protect against birds? Oct 5 '18 at 6:20
• Close an iris in front of the engine and you'll get an instant 100% loss of thrust, as well as possibly a fan overspeed (the turbine will still be developing power while the fan cavitates in the partial vacuum behind the iris). Then when you want thrust again, the combusters will be flamed out and you'll have to restart -- which, low/slow/heavy, is a recipe for a crash. Warplanes do the same thing airliners do, if they detect birds that might hit: grit their teeth and keep flying the airplane. Oct 5 '18 at 11:27

The closing speeds are simply too high to be able to do anything.

A jet airliner is flying at an absolute minimum of 250km/h. Geese can fly at well over 50km/h, so you're looking at a potential closing speed of over 300km/h. Even if you could identify a bird a kilometer away as being a threat to your plane, that only gives you less than 12s to react, and that's under the completely unrealistic assumption that you can (a) spot a bird that's a kilometer away and (b) instantly determine whether or not it's going to hit you.

• Also, the birds can fight back. There was an incident (quite a long time ago) where a 747 was approaching Anchorage, Alaska. The flight crew identified a sea eagle ahead of them, flying the same course but somewhat slower, carrying a salmon held in its talons.. At the last minute, the eagle diverted out of the path of the plane - and dropped the salmon, which scored a direct hit on the #2 engine. Some you win, some you lose... Sep 26 '18 at 23:54
• @alephzero - That would be a fish strike, and they knew because a grizzly went after the #2 engine after parking, bad day for that 747 :P
– ymb1
Sep 27 '18 at 0:22
• @alephzero blog.alaskaair.com/alaska-airlines/history/flying-fish (not the engine, but a similar fish story) Sep 27 '18 at 1:02
• That's sounds a bit fishy Sep 27 '18 at 8:00
• @DonBranson Now now Don... just swim with the stream. Sep 28 '18 at 9:16

I think you hit the nail on the head there with the comment “if there’s time to react”. In many cases there just isn’t. Small birds are difficult to spot until they are right on top of you (generally <100 yards or so). Larger birds like geese or raptors can generally be spotted up to about 1/2 mile out or so, if you are alert for them.

Add to that that a passenger jet weighing anywhere between 40,000 lbs to 1,000,000+ lbs just ain’t that agile and moving along at 200-250 KIAS at low levels gives little time available to do this in (at 200 kts you cover about 110 yards per second or a football gridiron every second). Add into this cockpit tasks and flow, ATC communication, scanning for traffic, checklists, systems operation, lack of contrast between birds and the background, etc., and you quickly find you may not have a whole lot of time available for avoidance of feathered flyers.

Pilots will alert ATC if they spot flocks of birds which might present a hazard to other pilots. I’ve notified ATC about birds before, generally hawks and other raptors circling around the departure or approach ends of runways. Airports near known migratory routes for birds may publish advisories in aerodrome NOTAMs as well.

Cactus 1549 really didn’t have a prayer and was all over before either Sully or Stiles could really inititate evasive maneuvers. They also had the shock of the strikes to deal with (Sully claimed the birds impacts with the airframe produced a physical WHAM! WHAM! WHAM! effect, like being in a car being pelted with large hailstones during a severe thunderstorm, which is shocking and disorienting in and of itself). There was no time to evade the animals once they were spotted at close range. Any other conclusion is just musing by armchair pilots.

The only evasion technique I’ve been taught about birds is to climb away from them - the theory being when a bird gets scared or spooked in flight, it tucks its wings and dives rapidly to avoid predators, etc. I have no first hand evidence that that’s an effective evasion method; it may just be another aviation old wives tale.

Why is riding it out better than a bank? (Worst outcome is the same for doing nothing and doing something.)

From the article:

Bird strikes are a lesser hazard to aviation than other well-known hazards such as loss of control in flight, controlled flight into terrain, and runway excursions

Hitting birds is less likely to cause a serious accident than are the potential complications of sudden maneuvering. As a personal addendum, I've read about a lot more accidents caused by pilot error (including bad maneuvers) than by bird strikes.

It seems what Boeing recommends* is to ride it out then assess the damage.

You quoted their line Fly the airplane and maintain flight path control out of context. That is advice under "responses to a known or suspected bird strike", i.e. you've already hit the birds. Obviously, if the strike has already occurred, you can't maneuver away from it. Their point is to not let yourself get startled into altering your flight path. If you swerve, there's a chance of losing control of the aircraft - particularly if you've taken any damage from the strike. At this point, your best bet is to hold steady at least long enough to evaluate the damage that has already occurred.

Their main advice is mitigate the risk of strikes through careful planning - try to fly at altitudes where birds aren't a danger, be aware of common flight paths of birds, and check with local ATC for recent bird sightings.

I think you're misreading the technical language. Let me swap the order of the phrase to:

To avoid birds, avoid or minimize maneuvering at low altitude.

That is, avoid flying at low altitudes to minimize encounters with birds. "Maneuvering" is a technical term, put by the FAA as

the maneuvering phase of flight — turning, climbing, or descending close to the ground

An article by the Flight Safety Foundation expands on the idea to gain altitude to reduce bird encounters:

Hazard avoidance is superior to application of emergency procedures...

The majority of bird strikes occur below 3,000 ft. If departing from an airport in a high-bird-threat environment, jets should use International Civil Aviation Organization Noise Abatement Procedure 1.8 This rapid climb to above 3,000 ft above ground level would, in all likelihood, have prevented the US Airways accident. General aviation aircraft should depart at best angle-of-climb speed. Those techniques enable the aircraft to clear the hazard zone below 3,000 ft faster and climb at a lower speed, which can lessen the severity of impact. When landing in an area of high bird activity, the aircraft should remain at 3,000 ft or above if possible until necessary to descend for landing....

If the aircraft is capable of high-speed flight at low altitude … don’t do it.

Airliners operating near airports are flying at speeds which are low in relation to their stall speeds, but these speeds are high when it comes to recognizing and avoiding hazards. If the time between recognition of a hazard such as an impending bird strike and its occurrence is very short, a severe maneuver would be required for successful avoidance. Such a maneuver at low speed comes with a high risk of loss of control, asymmetric wing stall (and subsequent spin), etc.. Even at high altitude it may be unrecoverable, but at low altitude, there is no room for recovery at all. Light aircraft (piston propeller) typically fly slower, so they may have more time to react, so may therefore execute a successful avoidance with a controlled rather than abrupt maneuver. Also, such aircraft may have more speed margin so have less risk of stall (unless on/near final approach or just after takeoff).

Commercial flights are generally moving faster than 400 feet per second (About 270 MPH). In other words in less than two seconds they cover the distance of over the length of two football fields. Can you spot a couple of geese at 800 feet? Try it sometime on the ground. Pick an object about the size of a large bird that is not obscured at a distance and walk 800 feet away, then view it. Amazing how quickly things become a dot.

Another thing that happens is the eyes when processing a foreground that is solid such as clear blue sky or solid clouds tend to focus at about 30 feet in front of you. This means anything at 800 feet will be blurred to a soft fuzz.

Next is commercial birds do not turn on a dime. The mass is immense and trying to throw one into a fever pitch turn to avoid a bird strike has quite a bit of lag. Not only that you have passengers potentially up and moving, as well as the cabin crew. Sudden pitches will toss them around like rag dolls.

As rigid as the airframe is it also flexes quite a bit. That has a tendency to pop open the doors in the overhead stowage. Quick jerks will pop them and toss stuff which is not secured with straps. Flying objects in the cabin does not make for contented passengers nor contented corporate bean counters.

Lastly, all it takes is for one person to urp into an air sickness bag. Once one starts the effect rolls through the cabin. It is like a wave phenomena. If it starts at the front you can watch as successive rows begin shifting and grabbing bags just like a wave heading tot he back of the cabin. There is always one passenger with a fragile thin wall glass stomach and the least disturbance will sit off cabin wide airsickness.