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Comment by nostromo | Hacker News Reader

People keep saying a lightweight craft under six pounds poses no threat to commercial aviation, but is that really true?

I doubt a balloon with a circuit board could cause an engine to fail, but there are lots of sensitive measurement devices, like a pitot tube, that I imagine could fail if a balloon hit it. (For reference, Aeroperu 603 was brought down by tape that wasn't removed from the plane.)

I'm all about hobbyists hobbying, but it does seem like there should be at least some so of registration system so we know what people are launching into shared airspace.

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> People keep saying a lightweight craft under six pounds poses no threat to commercial aviation, but is that really true?

True enough for the extremely risk-averse FAA.

> there are lots of sensitive measurement devices, like a pitot tube, that I imagine could fail if a balloon hit it. (For reference, Aeroperu 603 was brought down by tape that wasn't removed from the plane.)

Tape over all of the multiply-redundant static ports on the aircraft. We don't treat tape as a critical threat to aircraft.

The 737-MAX has three pitot tubes and six static ports, deliberately placed on both sides of the aircraft. (https://www.researchgate.net/figure/Boeing-737-NG-and-MAX-pr...)

But only 1 angle of attack sensor on some models …

No, but that's fine, because Boeing needs to make money upselling carriers on redundancy.

No, the 737 Max has 2 AoA sensors, it just used a bizarre “only use one at a time and ignore the other” approach to (non) redundancy.

If only that was the worst design issue with the 737 Max... It is astonishing how Boeing got away with that clusterfuck of a plane. All because they didn't wan't to invent a new body and beat Airbus to market.

> People keep saying a lightweight craft under six pounds poses no threat to commercial aviation, but is that really true?

Most likely.

Even more so for lighter than air aircraft. An airliner traveling at Mach 0.8 would most most likely push this tiny thing out of the way like a feather even if it was in the flight path.

Note that, regarding your pitot tube example, they are _pointy_. And heated. Assuming the balloon would even be hit and have its fabric intact, it would still be punched right through.

Remember, 90000 pound aircraft traveling at Mach 0.8 (for an average 737) against a lighter than air balloon where the most rigid components are small circuit boards and thin solar panels. There isn't even an electronics case in most instances.

Maybe engines would ingest it, but they wouldn't even notice.

> Maybe engines would ingest it, but they wouldn't even notice.

Someone once told me, but I can't remember whether it was an aviator or an ornithologist, that a bird with a metal ring on its leg could cause total destruction of a jet engine. Of course they don't attach metal rings to birds any more and haven't done so for a long time, and I'm not sure how big the risk was even with the chunkiest of old-fashioned rings.

(What about a bird with an arrow stuck through it, I wonder? https://en.wikipedia.org/wiki/Pfeilstorch )

Bird Ingestion Tests [0] are performed with a chicken gun™ in order to test the damage a bird would do to the engine. They don't put metal rings on them though !

https://www.youtube.com/watch?v=rSafRuLB0c0

I imagine it would destroy an engine on ingest, but that doesn't mean the plane goes down. They can fly with just one engine. It's hard, and they land ASAP, but nobody dies.

Ya but if people are allowed to put up small craft as they please there's a much greater chance of the plane encountering and ingesting another small craft as it gets closer to a location for emergency landing

>aircraft traveling at Mach 0.8 (for an average 737) against a lighter than air balloon where the most rigid components are small circuit boards

>they wouldn't even notice

What?

Imagine an aircraft sitting stationary on the runway and you fire a circuit board at it at mach 0.8, which is 988km/h or 274m/s. It's the same thing.

From google, an arduino pro micro, which is a small circuit board, about the size of a usb flash drive, weighs 13g.

From wikipedia, a .22 bullet weighs 1.3 to 3.9 g, so about 1/10 of that small circuit board, and goes at a velocity of 175 to 533 m/s.

Do you really think that's safe?

Would you be happy to fly in a plane where they shot at it with ten rifles before you get in?

The pitot and static are usually redundant.

In the case of Aeroperu, it was being serviced, and so _all_ the static ports were taped over with duct tape. Which is an extremely unusual maintenance procedure and resulting failure mode, and in flight you wouldn't expect all of them to fail simultaneously, even after an impact with an foreign object.

And critically, in their case, the ground radar warning system was working; however, due to all the other failures and alarms occurring on the flight deck, they did not notice or did not pay attention to this alarm.

Modern aviation is so filled with redundancies and double checks that most disasters are the result of a long sequence of chained failures, and not due to a single piece of equipment becoming inoperative.

Don't forget that they usually travel at 2x the flight ceiling of an airliner. The transition up and down is really quick. So the effective risk is low. And usually you can inform the authorities so they know where it is.

But people have been doing it for decades and most people didn’t even know about them so maybe everyone’s making a deal of a non-problem?

There is no real problem here, and knee-jerk over-regulating won't help anything.

That small drones and hobby R/C planes need fucking transponders in the US is bloody insane.

Seeing aliens or Soviets in every birthday balloon that escapes into the wild blue yonder is ridiculous.

A single bird can cause an engine to fail so...

Improbable unless it's a really enormous bird (or many large birds at one time). A chicken wouldn't be big enough. Bird ingestion would probably cause some damage that would have to be repaired, but jet engines are tested for this exact scenario. And engines are tested for large birds and both medium and small engine flocks.

Sure, it _could_ happen with a single bird, but it probably won't.

https://www.law.cornell.edu/cfr/text/14/33.76

I'm sure that Sully flight is much more confident that they didn't crash due to dual engine loss from bird strike thanks your comment.

To pile on, the average weight of male Canadian Geese is > 8 pounds, which is higher than the largest 'large bird' that needs to be tested, and they travel in flocks. I think they worked out that each engine probably ingested two birds. At the time those engines were certified, the largest bird tested was 4 lbs and they only volleyed them into the outer area of the engine, not the core where the accident engines hit.[1]

Now they have to send them into the 'most critical area' of the engine, but depending on engine size the largest bird tested could still be 4 or 6 lbs.

[1] https://www.ntsb.gov/investigations/accidentreports/reports/...

By "tested", do you mean someone out there has the somewhat insane job of throwing actual birds into fully-powered jet engines?

And I guess cleaning up afterward also?

They use a chicken gun, but yes… https://en.m.wikipedia.org/wiki/Chicken_gun

One of the timeless mythbuster bits too.

Engines are tested exactly for the scenario of ingesting a small bird, yes.

Not for ingesting a large Mylar balloon with a mass tied to one end, necessarily.

Engines are also tested for speeds and altitudes where birds are typically encountered - ie, not Mach 0.8 at FL35. Canopy tests are similar.

If I’m remembering correctly, I think the typical “speed limit” is 250 kts below Class A airspace, which is a far cry from a Mach number.

edit: I also recall that the testing allows for destruction of the engine as long as shrapnel does not penetrate the fuselage. Engines are not happy ingesting a goose regardless of speed or altitude. There’s a liner surrounding the turbine blades the must remain intact to pass the test.

Single engine failure is trained for quite extensively by pilots. Even 747 pilots regularly train for a dual engine failure on the same side landing.

Reminds me of the joke where an engineer is testing cockpit windshield resistance to bird-strike by firing dead chickens at it from a special cannon. The windshields keep shattering and they wonder why.

One engineer suggests that they probably defrost the chicken first.

All kinds of FOD (foreign object damage) can cause issue, regardless of its size or material. Look at what damage a small bird can deal, especially to a jet engine.

> six pounds poses no threat to commercial aviation, but is that really true?

It's because that's half the weight of a Canadian Goose.

Hitting a flock of birds can take out an engine tho.

What about hitting half a goose?

Here's some bird ingestion data for you from the certification of a GE90 Engine (large commercial airliner engine)

"As part of the required certification testing, the GE90 successfully completed both the 2.5 and 8 lb. (1.13 and 3.63 kg) bird ingestion tests on the engine’s composite blades. In October 94, four 2.5 lb. birds were ingested with the engine running at speeds required to produce 85,000 lb. (377.8 kN) of thrust at takeoff on a hot day. There was no thrust loss and the engine responded to all throttle commands during the required 20 minutes of operation following the ingestion."

https://www.easa.europa.eu/en/downloads/7799/en https://www.kimerius.com/app/download/5781574315/The+GE90+-+...

the point is birds don't need a license to fly, so balloons with that payload weight shouldn't either

Hitting a single bird can take down a plane. Here's some cockpit footage:

https://www.youtube.com/watch?v=rNqU8jfAJMQ

Here's that didn't take down the plane, but made a big hole in the canopy spewing blood and guts all over the person in the back seat with the body hitting them in the shoulder.

https://www.youtube.com/watch?v=XAn6yBJjC8g

Pitot tubes are rigid components with no moving parts involved in its mechanism. They aren't that fragile.

Collision with a bird can take down a fighter jet. So a circuit board can probably do that too

If these have low radar signature, and they are below 60k feet then they could be a problem at least at night, and maybe during the day too

https://udayton.edu/udri/news/18-09-13-risk-in-the-sky.php

Thats just a 2lb drone and it rips into the leading edge of a small craft, imagine at 500+ mph.

Another good example is the Columbia disaster; it was just a piece of foam

> Another good example is the Columbia disaster; it was just a piece of foam

Icy foam knocking a tile loose is not a critical problem for an airplane.

That's not the point and you know it. Don't be pedantic. It doesn't help the conversation. The above poster is saying that even small problems can lead to catastrophic consequences in complicated machines.

I'm not being pedantic. I'm pointing out that the example is a corner case that is irrelevant to this topic.

> The above poster is saying that even small problems can lead to catastrophic consequences in complicated machines.

That's a very generic statement. Are you sure that was their real point? Not something more specific to air strikes?

It was my point, and i thought it was clear enough that it was just a comparison of projectile to target, and the damage a tiny object can cause; I should have added more words, maybe. Most at NASA thought that the foam couldn't have damaged the spacecraft, and they were wrong.

If a drone penetrates the wing, we don't really know if it can make it to the fuel tank when it hits at 500...

If your point is "small problems can lead to catastrophic consequences in complicated machines" then it's not helpful, because we have more specific information for planes that overrides such a generic statement.

> The above poster is saying that even small problems can lead to catastrophic consequences in complicated machines.

Sure, but they picked an example that's outside of this kind of aircraft's spec, so it's not clear that it's applicable. Bad examples deserve to be called out.

Who's being pedantic here? The conversation is about a complete fiction, since a balloon never caused an airliner to crash. Why do we have to entertain that scenario that never actually happened, and how does that help the conversation about the danger of balloons to air traffic?

Yeah... your typical aircraft is not reaching Mach 20 where a hole would cause high temperatures leading to structural failure. Concerns about balloons and such can be valid but a comparison to Columbia is a big stretch.

Clearly i should have added more words as I thought it was obvious I was just comparing projectile vs target; ie, just because an object is small or light doesn't mean it can't cause significant damage, and we don't have a lot of research into it.

If it penetrates the wing, can it hit the fuel tank?

And 6lb of metal hits different than 6lb of goose, depending on what it hits. Hail can destroy a radome.

Fuel tanks are kevlar-lined nowadays, no? Certainly that doesn't make them invulnerable, but they can take quite a beating before they start leaking or worse.

"My club's hobby is testing how small/flimsy an object can be to bring down an airliner and kill hundreds of innocent people."

And so far the club hasn't managed to get even one person killed.

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